JournalTOCs

Physics of Plasmas
Journal Prestige (SJR): 0.576

Citation Impact (citeScore): 1
Number of Followers: 10

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1070-664X - ISSN (Online) 1089-7674
Published by AIP

[27 journals]

Virial relations for elongated plasmas in a tokamak and their potential
use in magnetic diagnostics
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  Authors: V. D. Pustovitov
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Virial relations are traditionally considered as providing the diamagnetic parameter, poloidal beta [math], and internal inductance [math] through the integrals determined by the plasma shape and poloidal magnetic field at the plasma–vacuum interface. This gives rise to discussions of their potential applications for diagnostic purposes. Recently, this concept was analyzed in the numerical study of Bongard et al. [Phys. Plasmas 23, 072508 (2016)]. Here, we analytically calculate three main virial integrals (traditionally denoted as [math], [math], and [math]) for the plasma with elliptical cross section. The results are expressed through the plasma elongation, its radial derivative, and a similar derivative [math] of the Shafranov shift, all taken at the plasma boundary. The geometry of magnetic surfaces inside is not constrained, which guaranties the applicability of the results in a wide area. It is shown that [math] must be a constant, [math] weakly depends on [math], and only [math] is a sensitive function of the plasma state through [math]. This makes [math] the quantity most suitable for diagnostics, while independence of [math] on the plasma shape, [math], and [math] can be good for calibrations. The difficulties of inferring [math] from the measured [math] are now shown explicitly.
  Citation: Physics of Plasmas
  PubDate: 2022-09-23T09:46:59Z
  DOI: 10.1063/5.0109492
Dynamics of implosion phase of modified plasma focus studied via laser
interferometry and electrical measurements
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  Authors: J. Malir, D. Klir, J. Cikhardt, J. Kravarik, P. Kubes, V. Munzar, J. Novotny, K. Rezac, M. Paduch
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Dynamics of the implosion of the dense plasma focus play an essential role in converting electrical energy into the kinetic energy of the current sheath and subsequent production of accelerated electrons, ions, hard X-ray, and neutron emission. This paper presents the analysis of the implosion parameters, such as the implosion velocity and imploding mass, coupled with electrical parameters observed on the PF-1000 facility with a modified electrode system. The first two parameters are based on the 16-frame Mach–Zehnder interferometer, which provides the spatial distribution of electron density in a time sequence. Measurement of the total current, current derivative, and voltage enables us to evaluate the total inductance and kinetic energy driven by the capacitor bank. Then comparing the inductances and kinetic energies evaluated from the interferograms and electrical waveforms can provide more precise information on the current flowing in the imploding sheath. We present a possible way to deal with the fact that only part of the total current flows through the imploding layer. With the supposition that the rest of the current flows close to the insulator, we conclude that roughly 70% of the total current flows through the pinch, which is in good agreement with an input parameter of the Lee model, for example.
  Citation: Physics of Plasmas
  PubDate: 2022-09-23T09:46:58Z
  DOI: 10.1063/5.0098124
Theory of the magnetothermal instability in coronal plasma flows
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  Authors: F. García-Rubio, R. Betti, J. Sanz, H. Aluie
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The theory of the magnetothermal instability (MTI) [D. A. Tidman and R. A. Shanny, Phys. Fluids 17, 1207 (1974)] is revisited through the lens of the stability of uniform systems. The linear stability analysis includes flow advection and Nernst transport. The instability criteria derived distinguish between the convective and the absolute nature of the perturbation growth. It is proven that, in the region where the Nernst and plasma blowoff velocities cancel, the MTI can be absolute and wave-packet perturbations grow in situ. This instability is mediated by the internal feedback between the Biermann battery and Righi–Leduc terms. The analysis is extended to derive the dispersion relation for short-wavelength perturbations developing in nonuniform profiles with the application to coronal plasmas. It is found that the condition for MTI requires the net B-field convection velocity to be small at the isothermal sonic section, and the plasma conditions in this section govern the dynamics of the instability. Analysis of hydro-equivalent implosions suggests that unstable perturbations undergo more e-foldings of growth in larger-size targets.
  Citation: Physics of Plasmas
  PubDate: 2022-09-23T09:46:56Z
  DOI: 10.1063/5.0109877
Numerical implementation of the improved Sugama collision operator using a
moment approach
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  Authors: B. J. Frei, S. Ernst, P. Ricci
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The numerical implementation of the linearized gyrokinetic and drift-kinetic improved Sugama (IS) collision operators, recently introduced by Sugama et al. [Phys. Plasmas 26, 102108 (2019)], is reported. The IS collision operator extends the validity of the widely used original Sugama (OS) operator [Sugama et al., Phys. Plasmas 16, 112503 (2009)] to the Pfirsch–Schlüter collisionality regime. Using a Hermite–Laguerre velocity–space decomposition of the perturbed gyrocenter distribution function that we refer to as the gyro-moment approach, the IS collision operator is written in a form of algebraic coefficients that depend on the mass and temperature ratios of the colliding species and perpendicular wavenumber. A comparison between the IS, OS, and Coulomb collision operators is performed, showing that the IS collision operator is able to approximate the Coulomb collision operator in the case of trapped electron mode in H-mode pedestal conditions better than the OS operator. In addition, the IS operator leads to a level of zonal flow residual which has an intermediate value between the Coulomb and the OS collision operators. The IS operator is also shown to predict a parallel electrical conductivity that approaches the one of the Coulomb operator within less than 1%, while the OS operator can underestimate the parallel electron current by at least 10%. Finally, closed analytical formulas of the lowest order gyro-moments of the IS, OS, and Coulomb operators are given, which are ready to use to describe the collisional effects in reduced gyro-moment fluid models.
  Citation: Physics of Plasmas
  PubDate: 2022-09-22T11:43:01Z
  DOI: 10.1063/5.0091244
Comment “On the dose of plasma medicine: Plasma-activated medium (PAM)
and its effect on cell viability” [Phys. Plasmas 29, 063506 (2022)]
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  Authors: Jaroslav Julák
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  
  Citation: Physics of Plasmas
  PubDate: 2022-09-22T02:51:09Z
  DOI: 10.1063/5.0109538
Response to “Comment on ‘On the dose of plasma medicine:
Plasma-activated medium (PAM) and its effect on cell viability’”
[Phys. Plasmas 29, 094701 (2022)]
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  Authors: Xinpei Lu, He Cheng
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  
  Citation: Physics of Plasmas
  PubDate: 2022-09-22T02:51:07Z
  DOI: 10.1063/5.0119854
Publisher's Note: “Collective plasma effects of electron–positron
pairs in beam-driven QED cascades” [Phys. Plasmas 29, 042117 (2022)]
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  Authors: Kenan Qu, Sebastian Meuren, Nathaniel J. Fisch
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:59:12Z
  DOI: 10.1063/5.0124570
Publisher's Note: “JOREK3D: An extension of the JOREK nonlinear MHD code
to stellarators” [Phys. Plasmas 29, 063901 (2022)]
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  Authors: N. Nikulsin, R. Ramasamy, M. Hoelzl, F. Hindenlang, E. Strumberger, K. Lackner, S. Günter
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:59:11Z
  DOI: 10.1063/5.0124567
Onset of instability with collapse observed in relatively high density and
medium beta regions of LHD
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  Authors: Yuki Takemura, Kiyomasa Watanabe, Satoru Sakakibara, Satoshi Ohdachi, Yoshiro Narushima, Kenji Tanaka, Tokihiko Tokuzawa
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Edge MHD instabilities with pressure collapse are found in relatively high beta and low magnetic Reynolds number regions with a magnetic axis torus outward-shifted configuration of the large helical device (LHD), and characteristics and onset conditions of the instability are investigated. The instability has a radial structure with an odd parity around the resonant surface, which is different from that of the interchange instability typically observed in the LHD. The onset condition dependence on the magnetic axis location shows that the onset beta increases as the magnetic axis location moves more torus inwardly, and the instability appears only in limited configurations where the magnetic axis is located between 3.65 and 3.775 m. In such configurations, the resonant surface location is close to an index of the plasma boundary. This fact suggests that the distance between the resonant surface location and the plasma boundary plays an important role in the onset, and a possibility that the instability is driven by an external mode.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:57:39Z
  DOI: 10.1063/5.0111360
Quasilinear theory of general electromagnetic fluctuations including
discrete particle effects for magnetized plasmas: General analysis
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  Authors: R. Schlickeiser, P. H. Yoon
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The general quasilinear Fokker–Planck kinetic equation for the gyrophase-averaged plasma particle distribution functions in magnetized plasmas is derived, making no restrictions on the energy of the particles and on the frequency of the electromagnetic fluctuations and avoiding the often made Coulomb approximation of the electromagnetic interactions. The inclusion of discrete particle effects breaks the dichotomy of nonlinear kinetic plasma theory divided into the test particle and the test fluctuation approximation because it provides expression of both the non-collective and collective electromagnetic fluctuation spectra in terms of the plasma particle distribution functions. Within the validity of the quasilinear approach, the resulting full quasilinear transport equation can be regarded as a determining nonlinear equation for the time evolution of the plasma particle distribution functions.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:57:36Z
  DOI: 10.1063/5.0104709
Effects of solar flares on ionospheric TEC over Iceland before and during
the geomagnetic storm of 8 September 2017
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  Authors: Chali Idosa, Kebede Shogile
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The effects of solar flares on ionospheric total electron content (TEC) over Iceland before and during the geomagnetic storm of September 8, 2017 were studied. Global Positioning Syste (GPS)-TEC data were obtained from dual-frequency GPS sites operated by the University NAVSTAR Consortium at Dyna (65.06°N, −16.6°E) and Kisa (64.7°N, −17.6°E) stations. The findings of this study show that the enhancement of ionospheric TEC was more noticeable over the Kisa station than over the Dyna station during the coronal mass ejection day. However, during the geomagnetic storm day, maximum enhancement of TEC was observed over the Dyna station than over the Kisa station. The values of the ionospheric TEC during the initial phase of the storm were greater than during the main and recovery phases of the storm over both stations. This might be due to the effects of X-class solar flares and shock wave preceding the arriving of interplanetary coronal mass ejections plasma. The spatial gradients of TEC between two nearby stations are similar during the main phase of the storm, but slightly different during the initial and recovery phases of the storm. Finally, solar events have a favorable influence on geomagnetic storm indices and ionospheric observables.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:57:35Z
  DOI: 10.1063/5.0098971
Beam-driven whistler mode nonlinear saturation and turbulence in the
magnetopause
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  Authors: Jyoti, Suresh C. Sharma, Neha Pathak, R. P. Sharma
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  This work presents a model to understand the generation of whistler turbulence in the magnetic reconnection region of magnetopause by the energetic electron beams (generated by magnetic reconnection process) as observed by magnetospheric multiscale mission [Zhao et al., J. Geophys. Res.: Space Phys. 126, e2020JA028525 (2021)]. In this model, the magnetic reconnection process has been replaced by the energetic electron beam source. Hence, the beam-driven whistler-mode dynamical equation has been set up by anticipating that it will grow from noise level due to beam energy and then will attain large amplitude such that nonlinear effects due to ponderomotive force will lead to the localization of whistler waves, and finally, this will lead to the turbulent state. For this, a non-linear two-dimensional fluid model is developed in which nonlinear interaction between high-frequency whistler wave and low-frequency ion acoustic wave (IAW) is pertinent to the magnetopause region. Due to large-amplitude whistler waves, ponderomotive force components emerge, which are included in IAW's nonlinear dynamics. The system of the dimensionless equations consists of the dynamics of whistler wave and IAW, and this has been solved by the numerical method. The results of the simulation show that the whistler's temporal evolution results in localized structures that eventually lead to turbulence. The relevance of the present investigation to the recent observations has also been pointed out.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:07:42Z
  DOI: 10.1063/5.0098108
Experimental studies of a novel one-dimensional plasma window
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  Authors: Xiuming Yu, Xiaoyi Yang, Chijie Xiao, Min Xu, Renchuan He, Tianchao Xu, Yue Ge, Zuyu Zhang, Mingyang Wu, Yi Yu, Kun Zhu, Xiaogang Wang
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The plasma window is a windowless vacuum sealing device that utilizes a cascade arc discharge to isolate regions with different pressures. It was proposed as an alternative to the traditional windowless sealing technology of differential pumping, which greatly improves the sealing efficiency and has been successfully applied in electron beam welding. The discharge channel of the existing plasma window is a small circular hole, referred to as a zero-dimensional plasma window, which has limited applications to its dimensions. In this study, we suggested a one-dimensional (1D) plasma window with a slit discharge channel (cross section: 3 × 35 mm2, length: 60 mm). An arc discharge is realized with the support of an 80 A DC power supply, which can maintain a pressure drop of more than 10 times between the high-pressure and low-pressure ends of the plasma window. A COMSOL-based magneto-hydrodynamic model of the plasma window was established, and simulations were in good agreement with the experimental results. The pressure drop in the plasma window caused by argon plasma has also been theoretically analyzed and discussed. The feasibility of a 1D plasma window to achieve vacuum isolation was verified theoretically, numerically, and experimentally.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:06:24Z
  DOI: 10.1063/5.0100064
Experimental research on a diode packaged with a compact and lightweight
permanent magnet
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  Authors: Yufang He, Junpu Ling, Juntao He, Lei Wang, Lili Song
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  In order to make the high-power microwave sources packaged with a permanent magnet more compact and miniaturized, we design a novel compact and lightweight permanent magnet package based on a C-band coaxial transit time oscillator. Before conducting the microwave generation experiment, research on the emission and transmission is carried out. In the beam transmission experiment, when the compact and lightweight permanent magnet is applied, the transmission efficiency in the diode is only 68.1%, while a phenomenon of side emission of electron beams is observed. When a solenoid is used, no side emission occurs. We theoretically analyze this experimental phenomenon and conclude that the radial magnetic field generated by the permanent magnet aggravates the side emission on the surface of a cathode holder. To solve this problem, a novel diode with a gradient cathode holder is proposed. In the beam transmission experiment using the compact and lightweight permanent magnet, this diode can suppress the side emission of electron beams, and the transmission efficiency in the diode is increased to 80.7%. The potential of the diode proved to work efficiently with this permanent magnet package, laying the foundation for the experimental research of microwave generation with this permanent magnet.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:06:22Z
  DOI: 10.1063/5.0098653
Mapping the power-law decay of high-harmonic spectra from few-cycle
laser–solid interactions
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  Authors: Shikha Bhadoria, Thomas Blackburn, Arkady Gonoskov, Mattias Marklund
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Visible or near infrared light can be manipulated to produce bursts of coherent extreme ultraviolet or x rays via the relativistic high-order harmonic generation process when a laser irradiates a solid plasma target. The intensity of the spectral components of the reflected signal decays with the increase in harmonic order and the efficiency of this non-linear process largely hinges on how prompt this decay is. This is governed by the conditions of the laser–plasma interaction for which various models have been proposed. At relativistic intensities, a spectrum exhibiting a power-law decay with an exponent of 8/3 or 4/3 is often stated. Here, we analyze the dependence of this exponent on interaction parameters, including the angle of incidence, the carrier envelope phase, intensity of the laser, and the pre-plasma length, and discuss opportunities for optimization. Our simulations show that, rather than there being one universal exponent, the spectral decay is a continuous function of the laser–plasma interaction parameters.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T12:06:22Z
  DOI: 10.1063/5.0087854
Achieving a social license for fusion energy
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  Authors: Seth A. Hoedl
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Despite recent technical advances, there is a risk that commercial-scale fusion will not play a substantial role in mitigating climate change or alleviating energy poverty due to a lack of public or community support, often referred to as a lack of a social license. This risk is not academic—other technologies, such as fission reactors, spent fuel waste repositories (e.g., Yucca Mountain), genetically modified foods, onshore and offshore wind turbines, electrical transmission lines, and even vaccines, struggle due to rejection by a substantial fraction of society, in other words, a lack of social acceptance. Conventional approaches to this challenge, such as risk-reducing technical solutions (e.g., replacing fission with fusion), or better “communication” or “education,” are unlikely, on their own, to be sufficient to mitigate this risk. Fortunately, fusion is sufficiently young that it has an opportunity to distinguish itself from other energy technologies not just in the way that it uses physics, but also in the way that it approaches society. In particular, fusion can anticipate, rather than react to, public concerns. Looking to other industries and fields of research, this paper describes the risk of a lack of public support and methods to achieve such support, including a social license, bio-ethical review, and responsible research and innovation. These methods are discussed in the context of seven case studies, illustrating practical application. The paper concludes with recommendations for specific steps that fusion companies, non-governmental organizations, academic researchers, government funders, and government regulators can take now to facilitate a long-term social license for fusion energy.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T11:17:22Z
  DOI: 10.1063/5.0091054
The effect of humidity on the discharge mode transition of air discharge
plasma
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  Authors: Wang Xi, Santu Luo, Dingxin Liu, Zifeng Wang, Zhijie Liu, Li Guo, Xiaohua Wang, Mingzhe Rong
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Cold atmospheric plasma in air commonly operates in the O3 mode and NOx mode, which easily interconvert through a transition mode, depending on discharge conditions. Given that the humidity varies considerably in different weather, it is important to elucidate the effect of humidity on the discharge mode transition, but few studies have been reported thus far. In this study, air plasmas were generated by a surface dielectric barrier discharge with different discharge powers of 6, 9, and 12 W, and the relative humidity of air was controlled at 1.5% (dry air), 40%, or 80% for a comparative study. It was found that an increase in humidity suppressed the production of O3 but promoted that of NO2 when the discharge power was 6 W, whereas it promoted the production of O3 but suppressed that of NO2 when the discharge power was 12 W. This implies that air humidity could have a bidirectional effect on the discharge mode transition, which was validated by experiments with a moderate power of 9 W. In that case, the discharge in dry air maintained the transition mode at a quasi-stable state, but it transited either into the NOx mode when the humidity was 40% or into the O3 mode when the humidity was 80%. A competition between reaction pathways dominated by N2(ν) or water-originated compounds may be the cause, and our findings indicate that the effect of humidity should be taken seriously in the research and development of air discharge plasmas.
  Citation: Physics of Plasmas
  PubDate: 2022-09-21T11:17:21Z
  DOI: 10.1063/5.0107803
Erratum: “A universal theory for gas breakdown from microscale to the
classical Paschen law” [Phys. Plasmas 24, 113522 (2017)]
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  Authors: Amanda M. Loveless, Allen L. Garner
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:10:12Z
  DOI: 10.1063/5.0121626
Sheath expansion effect of double flush mounted probe in weakly ionized
plasma
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  Authors: Pengcheng Yu, Yu Liu, Xiangqun Liu, Jiuhou Lei
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Sheath expansion is a distinctive feature of the double flush mounted probe because of the embedded configuration. Previously, the sheath expansion effect was usually neglected in weakly ionized plasma dominated by collisions between charged particles and neutrals. In this work, we investigated the sheath expansion effect of the double flush mounted probe in weakly ionized plasma. Results indicate that measurements using the double flush mounted probe were also influenced to a certain extent by the sheath expansion effect in weakly ionized plasma. To eliminate the influence, an empirical analytical formula has been presented to eliminate the influence of sheath expansion. In addition, a fitting curve is given based on experimental data, which indicates that sheath expansion should be considered in processing the measured data when the plasma pressure is lower than 200 Pa. In summary, this work indicates that the ion–neutral collision is a crucial factor that affects sheath expansion in addition to the radius parameter and probes' bias, which can be extended to double flush mounted probe diagnostics in collisional plasma such as the reentry plasma sheath and high-powered plasma thruster.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:10:11Z
  DOI: 10.1063/5.0099065
Modeling results on the dust charge distribution in a plasma afterglow
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  Authors: I. B. Denysenko, M. Mikikian, N. A. Azarenkov
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Discharging of dust particles in an argon plasma afterglow is investigated using different approaches. First, the dust charge distribution function (DCDF) is obtained by solving numerically the master equation describing dust discharging as a one-step stochastic process. Second, the DCDF is calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. Additionally, the time-dependencies for the mean dust charge are obtained assuming that the charge changes continuously in the afterglow plasma. Calculation results are compared with available experimental data and are found to be in good qualitative agreement if the dust discharging model accounts for the emission of electrons in the collisions of excited argon atoms with dust particles. This study is carried out taking into account the transition from ambipolar to free diffusion as well as multistep ionization, excitation, and deexcitation of argon atoms in the plasma afterglow.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:10:09Z
  DOI: 10.1063/5.0100913
Resonant alpha particle loss in stellarators
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  Authors: Roscoe White
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Particle resonances in stellarators can produce islands in the space of passing particle orbits without the presence of an unstable Alfvén mode, provided the period of the resonance matches the period of the equilibrium magnetic field. In this case, the equilibrium itself plays the role of a mode amplitude, and the islands appear on surfaces where the orbital helicity matches the field period. At low energy, these surfaces are given by the field line helicity, but at higher energy, cross field drift causes them to move. The resonances are also felt by trapped particles bouncing back and forth on surfaces with matching helicity. The periodic variation of B along these orbits produces local wells, giving loss due to drift while trapped in a well. Stellarator designs that have equilibrium-induced resonance islands exhibit anomalous alpha particle loss and are unsuitable for reactors.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:06:50Z
  DOI: 10.1063/5.0104923
Suppression of reconnection in polarized, thin magnetotail current sheets:
2D simulations and implications
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  Authors: Xin An, Anton Artemyev, Vassilis Angelopoulos, Andrei Runov, San Lu, Philip Pritchett
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Many in situ spacecraft observations have demonstrated that magnetic reconnection in the Earth's magnetotail is largely controlled by the pre-reconnection current sheet configuration. One of the most important thin current sheet characteristics is the preponderance of electron currents driven by strong polarized electric fields, which are commonly observed in the Earth's magnetotail well before the reconnection. We use particle-in-cell simulations to investigate magnetic reconnection in the 2D magnetotail current sheet with a finite magnetic field component normal to the current sheet and with the current sheet polarization. Under the same external driving conditions, reconnection in a polarized current sheet is shown to occur at a lower rate than in a nonpolarized current sheet. The reconnection rate in a polarized current sheet decreases linearly as the electron current's contribution to the cross-tail current increases. In simulations with lower background temperature, the reconnection electric field is higher. We demonstrate that after reconnection in such a polarized current sheet, the outflow energy flux is mostly in the form of ion enthalpy flux, followed by electron enthalpy flux, Poynting flux, ion kinetic energy flux, and electron kinetic energy flux. These findings are consistent with spacecraft observations. Because current sheet polarization is not uniform along the magnetotail, our results suggest that it may slow down reconnection in the most polarized near-Earth magnetotail and thereby move the location of reconnection onset downtail.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:06:49Z
  DOI: 10.1063/5.0088064
Slow electron holes in the Earth's bow shock
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  Authors: S. R. Kamaletdinov, I. Y. Vasko, R. Wang, A. V. Artemyev, E. V. Yushkov, F. S. Mozer
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  We present analysis of about one hundred bipolar structures of positive polarity identified in ten quasi-perpendicular crossings of the Earth's bow shock by the Magnetospheric Multiscale spacecraft. The bipolar structures have amplitudes up to a few tenths of local electron temperature, spatial scales of a few local Debye lengths, and plasma frame speeds of the order of local ion-acoustic speed. We argue that the bipolar structures of positive polarity are slow electron holes, rather than ion-acoustic solitons. The electron holes are typically above the transverse instability threshold, which we argue is due to high values of the ratio [math] between electron plasma and cyclotron frequencies. We speculate that the transverse instability can strongly limit the lifetime of the electron holes, whose amplitude is above a certain threshold, which is only a few mV/m in the Earth's bow shock. We suggest that electron surfing acceleration by large-amplitude electron holes reported in numerical simulations of high-Mach number shocks might not be as efficient in realistic shocks, because the transverse instability strongly limits the lifetime of large-amplitude electron holes at [math] values typical of collisionless shocks in nature.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:02:23Z
  DOI: 10.1063/5.0102289
Electron temperature gradient driven transport model for tokamak plasmas
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  Authors: T. Rafiq, C. Wilson, L. Luo, J. Weiland, E. Schuster, A. Y. Pankin, W. Guttenfelder, S. Kaye
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  A new model for electron temperature gradient (ETG) modes is developed as a component of the multi-mode anomalous transport module [Rafiq et al., Phys Plasmas 20, 032506 (2013)] to predict a time-dependent electron temperature profile in conventional and low aspect ratio tokamaks. This model is based on two-fluid equations that govern the dynamics of low-frequency short- and long-wavelength electromagnetic toroidal ETG driven drift modes. A low collisionality NSTX discharge is used to scan the plasma parameter dependence on the ETG real frequency, growth rate, and electron thermal diffusivity. Electron thermal transport is discovered in the deep core region where modes are more electromagnetic in nature. Several previously reported gyrokinetic trends are reproduced, including the dependencies of density gradients, magnetic shear, β and gradient of β [math], collisionality, safety factor, and toroidicity, where β is the ratio of the plasma pressure to the magnetic pressure. The electron heat diffusivity associated with the ETG mode is discovered to be on a scale consistent with the experimental diffusivity determined by power balance analysis.
  Citation: Physics of Plasmas
  PubDate: 2022-09-20T01:02:20Z
  DOI: 10.1063/5.0104672
Design of laser pulse shapes and target structures by random optimization
for direct-drive inertial confinement fusion
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  Authors: Z. Li, X. H. Yang, H. Xu, G. B. Zhang, B. Zeng, S. J. Chen, Y. Y. Ma, F. Y. Wu, J. Zhang
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Quasi-isentropic compression is required for inertial confinement fusion (ICF) to compress the target to a high density and high temperature status, where to match the laser pulse shape and target structure is of great significance to the implosion. However, many parameters for the laser pulse shape and the target structure should be optimized in order to realize such match. In this paper, the drive laser pulse and the target structure are designed using a random optimization method for a direct-drive ICF implosion driven by a 358.40 kJ laser pulse. This method can quickly optimize the laser pulse and target structure parameters for an efficient quasi-isentropic compression of the plasmas, leading to an areal density of 9.30% higher than that given by the hydrodynamic scaling. A correlation matrix is also constructed to analyze the correlation between the parameters. This provides a reference for further optimization and improvement. The method should have potential applications in the target design for future ICF experiments.
  Citation: Physics of Plasmas
  PubDate: 2022-09-19T10:47:02Z
  DOI: 10.1063/5.0096427
Ultimate transverse power of pulsed low-voltage gyrotron beam
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  Authors: Dun Lu, Wenjie Fu, Alexey Fedotov, Mikhail Glyavin, Mikhail Proyavin, Yang Yan
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Low operating voltage is highly attractive for medium-power millimeter-wave gyrotrons since it can reduce their size and cost, increase their safety, and, thus, improve usability for applications. However, at low voltages, the voltage depression caused by DC space-charge fields significantly limits the electron current and transverse power in the beam. Moreover, this current limitation is more pronounced for a beam with a higher pitch factor. As a result, for a given anode voltage, there is a pitch factor at which the transverse beam power in the gyrotron cavity is the maximum. This ultimate transverse power is found analytically in the non-relativistic approximation. Such a power is reached when the pitch factor calculated without taking into account voltage depression is only 0.82; voltage depression decreases the axial electron velocities, thus, increasing the actual pitch factor value in the cavity up to 1.4. As a result of this effect, high power and high efficiency cannot be obtained simultaneously in a low-voltage gyrotron. Using particle-in-cell simulations, two variants of low-voltage (5 kV) gyrotrons have been designed, namely, a device with higher power and an optimal pitch factor of 0.82 in the cavity and a device with a high pitch factor and high efficiency, but lower power.
  Citation: Physics of Plasmas
  PubDate: 2022-09-19T10:47:01Z
  DOI: 10.1063/5.0110498
Two-dimensional particle simulation of the boundary between a hot pair
plasma and magnetized electrons and protons: Out-of-plane magnetic field
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  Authors: M. E. Dieckmann, D. Folini, R. Walder, A. Charlet, A. Marcowith
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  By means of a particle-in-cell (PIC) simulation, we study the interaction between a uniform magnetized ambient electron–proton plasma at rest and an unmagnetized pair plasma, which we inject at one simulation boundary with a mildly relativistic mean speed and temperature. The magnetic field points out of the simulation plane. The injected pair plasma expels the magnetic field and piles it up at its front. It traps ambient electrons and drags them across the protons. An electric field grows, which accelerates protons into the pair cloud's expansion direction. This electromagnetic pulse separates the pair cloud from the ambient plasma. Electrons and positrons, which drift in the pulse's nonuniform field, trigger an instability that disrupts the current sheet ahead of the pulse. The wave vector of the growing perturbation is orthogonal to the magnetic field direction and magnetic tension cannot stabilize it. The electromagnetic pulse becomes permeable for pair plasma, which forms new electromagnetic pulses ahead of the initial one. A transition layer develops with a thickness of a few proton skin depths, in which protons and positrons are accelerated by strong electromagnetic fields. Protons form dense clumps surrounded by a strong magnetic field. The thickness of the transition layer grows less rapidly than we would expect from the typical speeds of the pair plasma particles and the latter transfer momentum to protons; hence, the transition layer acts as a discontinuity, separating the pair plasma from the ambient plasma. Such a discontinuity is an important building block for astrophysical pair plasma jets.
  Citation: Physics of Plasmas
  PubDate: 2022-09-19T10:46:59Z
  DOI: 10.1063/5.0106114
Enhanced analysis of experimental x-ray spectra through deep learning
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  Authors: D. A. Mariscal, C. M. Krauland, B. Z. Djordjević, G. G. Scott, R. A. Simpson, E. S. Grace, K. Swanson, T. Ma
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  X-ray spectroscopic data from high-energy-density laser-produced plasmas has long required thorough, time-consuming analysis to extract meaningful source conditions. There are often confounding factors due to rapidly evolving states and finite spatial gradients (e.g., the existence of multi-temperature, multi-density, multi-ionization states, etc.) that make spectral measurements and analysis difficult. Here, we demonstrate how deep learning can be applied to enhance x-ray spectral data analysis in both speed and intricacy. Neural networks (NNs) are trained on ensemble atomic physics simulations so that they can subsequently construct a model capable of extracting plasma parameters directly from experimental spectra. Through deep learning, the models can extract temperature distributions as opposed to single or dual temperature/density fits from standard trial-and-error atomic modeling at a significantly reduced computational cost compared to traditional trial-and-error methods. These NNs are envisioned to be deployed with high repetition rate x-ray spectrometers in order to provide detailed real-time analysis of experimental spectra.
  Citation: Physics of Plasmas
  PubDate: 2022-09-16T11:19:07Z
  DOI: 10.1063/5.0097777
Generation of collimated vortex gamma-rays from intense Poincaré
beam–plasma interaction
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  Authors: D. Younis, B. Hafizi, D. F. Gordon
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  We report on numerical calculations in which a multi-petawatt γ-ray beam is generated using a novel configuration based on fully structured light irradiating an overdense plasma waveguide. We analyze how the relativistic laser pulse efficiently confines and accelerates plasma electrons to GeV-scale energies and drives a quasi-static field that induces magneto-bremsstrahlung radiation. Multiphoton Compton scattering of electrons in the intense part of the laser also occurs although the radiated energy-density is comparatively lower. The emitted γ-rays carry orbital angular momentum, are highly collimated, and account for upwards of 15% of the incident field energy in one particular case. A comparison of the laser-to-particle angular momentum and energy transfer efficiencies is made between the cases of irradiation by a circularly polarized Laguerre–Gauss mode and one type of full Poincaré beam, and it is found that the latter yields an order-of-magnitude enhancement. The essential characteristics of the interaction are validated with three-dimensional particle-in-cell simulations that include quantum electrodynamical effects.
  Citation: Physics of Plasmas
  PubDate: 2022-09-16T11:19:06Z
  DOI: 10.1063/5.0102909
A numerical approach to the calculation of the Alfvén continuum in the
presence of magnetic islands
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  Authors: Axel Könies, Jinjia Cao, Ralf Kleiber, Joachim Geiger
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  A numerical approach is devised to calculate the shear Alfvén continuum inside and outside magnetic islands in cylindrical and stellarator plasmas. Equations for an appropriate set of coordinates and the arising equations for the continuum are derived and implemented in the CONTI code. An experiment-oriented representation of the results is chosen to allow a radial localization of the modes and a comparison of different magnetic configurations. Comparison is made with results of earlier analytic work for validation. Agreement is good but more details of the spectrum, such as the generation of island induced gaps inside and outside the separatrix, are found. While the code is easily usable and can be applied to any magnetic equilibrium accessible with VMEC, the calculations are plagued with convergence issues close to the separatrix. A calculation for a realistic W7-X equilibrium with islands is done where the island width is estimated with the HINT code.
  Citation: Physics of Plasmas
  PubDate: 2022-09-16T11:19:05Z
  DOI: 10.1063/5.0102239
Elimination of self-oscillation between three cascaded reflectors in an
X-band triaxial klystron amplifier
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  Authors: Fuxiang Yang, Fangchao Dang, Juntao He, Xingjun Ge, Jinchuan Ju, Xiaoping Zhang
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Self-oscillation of three cascaded reflectors easily occurs in a triaxial klystron amplifier (TKA) since the TEM mode leakage cannot be cut off by a coaxial waveguide. To solve this issue, we propose a non-uniform reflector to obtain an optimal external quality factor, which indicates its minimum TEM mode leakage. The self-oscillation of three non-uniform reflectors is then suppressed by selecting a specific drift tube length between them. Moreover, different eigenfrequencies are chosen for the three improved reflectors to enhance the tolerance of the drift tube length between them. With these methods, the self-oscillation of three cascaded reflectors can be successfully eliminated, and a TKA with high output efficiency is capable of achieving a long pulse output.
  Citation: Physics of Plasmas
  PubDate: 2022-09-15T12:34:19Z
  DOI: 10.1063/5.0101133
Specular reflections (“glint”) of the inner beams in a
gas-filled cylindrical hohlraum
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  Authors: N. Lemos, W. A. Farmer, N. Izumi, H. Chen, E. Kur, A. Pak, B. B. Pollock, J. D. Moody, J. S. Ross, D. E. Hinkel, O. S. Jones, T. Chapman, N. B. Meezan, P. A. Michel, O. L. Landen
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  We report on the experimental measurement of specular reflection (“glint”) of laser beams off the hohlraum wall in inertial confinement fusion experiments at the National Ignition Facility. In a hohlraum, glinted light can escape the opposite laser entrance hole of the hohlraum and is a potential laser energy loss mechanism. The total measured glint on the inner cones of beams is measured to be less than 8 TW (when using the full National Ignition Facility laser), which is
  Citation: Physics of Plasmas
  PubDate: 2022-09-15T12:10:19Z
  DOI: 10.1063/5.0099937
Arbitrary amplitude ion-acoustic supersolitons in negative ion plasmas
with two-temperature superthermal electrons
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  Authors: Kishan Kumar, M. K. Mishra
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Arbitrary amplitude ion-acoustic supersolitons are investigated with two-temperature superthermal electrons in an unmagnetized negative ion plasma. In this study, we have considered the plasma containing two cold ion species with different masses, ion concentration and charge multiplicity, and two superthermal (non-Maxwellian) electrons. The energy integral equation has been derived by using the Sagdeev pseudopotential technique. We have investigated that both negative and positive potential supersolitons and solitons can exist in the selected domain of Mach number. A numerical analysis shows that the ion-acoustic supersolitons appear below the acoustic speed [math]. The amplitude of the supersoliton is found larger than the soliton. The formation of solitons and supersolitons (both polarity) is analyzed by phase portrait of the dynamic of the plasma system. The plasma system also supports the coexistence of compressive and rarefactive solitons for a particular set of plasma parameters. The present study is focused on ion-acoustic solitary and supersolitary waves in the D-and F-regime of Earth's ionosphere and experimentally produced plasmas (Ar+, F−) and (Ar+, SF−6) ion species. The present investigation may be helpful in understanding the nonlinear behavior of supersoliton and soliton in space and laboratory plasmas, where negative ions are present with superthermal electrons at two temperatures.
  Citation: Physics of Plasmas
  PubDate: 2022-09-14T01:03:58Z
  DOI: 10.1063/5.0099053
Compensating cylindrical Hohlraum mode 4 asymmetry via capsule thickness
tailoring and effects on implosions
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  Authors: E. L. Dewald, D. S. Clark, D. T. Casey, S. F. Khan, D. Mariscal, P. Di Nicola, B. J. MacGowan, E. P. Hartouni, M. S. Rubery, C. Choate, A. Nikroo, V. A. Smalyuk, O. L. Landen, M. Ratledge, P. Fitzsimmons, M. Farrell, M. Mauldin, N. Rice
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Previously, hydrodynamic simulations [Clark et al., Phys. Plasmas 23, 072707 (2016)] suggested that precisely tailoring the capsule ablator thickness (shimming) could counterbalance cylindrical Hohlraum Legendre P4 drive asymmetries at the capsule in laser indirect drive implosions. As a result, the stagnated deuterium–tritium (DT) fuel areal density P4 asymmetry is reduced, potentially resulting in a nuclear yield increase. Inflight radiographs of various level of shimmed capsules with plastic (CH) ablators showed that shims can indeed control the in-flight capsule shell P4 asymmetry, with a linear sensitivity to shim amplitude that is close to analytic estimates and simulations. Furthermore, the stagnated DT fuel areal density P4 asymmetry inferred from downscattered neutron imaging was reduced when the capsule shim was applied, in agreement with simulations matching the inflight shell asymmetry. A nuclear yield improvement via shim was not observed, as predicted, likely due to implosion instabilities and as built capsule shim deviations from an ideal P4 shape.
  Citation: Physics of Plasmas
  PubDate: 2022-09-14T01:03:55Z
  DOI: 10.1063/5.0100095
Numerical analysis of structural change process in millimeter-wave
discharge at subcritical intensity
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  Authors: S. Suzuki, K. Hamasaki, M. Takahashi, C. Kato, N. Ohnishi
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Plasma-front propagation processes of 170 GHz millimeter-wave discharge were investigated under subcritical incident electric field intensity by using a one-dimensional model. The discharge structure was numerically reproduced at more than 0.2 MV/m by introducing the detailed chemical reaction and radiation transport processes into the conventional model. The results revealed that the propagation mechanism of the plasma front in the millimeter-wave discharge changes depending on the incident electric field intensity. At intensities greater than 1.4 MV/m, the plasma front propagated at supersonic speed, while forming a discrete structure, which has intervals of 1/4 wavelength of the millimeter wave. This structure was generated by electron-impact ionization and photoionization processes. At the intermediate intensities, the plasma front propagated continuously rather than discretely because the gas expansion increased the reduced electric field and induced electron-impact ionization. The dominant heating process at the plasma front was fast gas heating. At intensities less than 0.3 MV/m, the plasma front propagated continuously, but the dominant heating process changed to vibrational–translational relaxation. The discharge was maintained by thermal ionization and associative ionization. The simulation results were in good agreement with the past millimeter discharge experiments at this intensity.
  Citation: Physics of Plasmas
  PubDate: 2022-09-13T01:44:54Z
  DOI: 10.1063/5.0096363
Characterization of sub-picosecond laser-produced fast electrons by
modeling angularly resolved bremsstrahlung measurements with 3D hybrid
particle-in-cell code
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  Authors: L. Chen, H. Sawada
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Hard x-rays produced by intense laser-produced fast electrons interacting with solids are a vital source for producing radiographs of high-density objects and implosion cores for inertial confinement fusion. Accurate calculation of hard x-ray sources requires a three-dimensional (3D) simulation geometry that fully models the electron transport dynamics, including electron recirculation and the generation of absolute photon yields. To date, 3D simulations of laser-produced bremsstrahlung photons over tens of picoseconds and code benchmarking have not been performed definitively. In this study, we characterize sub-picosecond laser-produced fast electrons by modeling angularly resolved bremsstrahlung measurements for refluxing and non-refluxing targets using the 3D hybrid particle-in-cell (PIC), Large Scale Plasma code. Bremsstrahlung radiation and escaped electron data were obtained by focusing a 50-TW Leopard laser (15 J, 0.35 ps, 2 × 1019 W/cm2) on a 100-μm-thick Cu foil and a Cu with a large plastic backing (Cu–CH target). Data for both the Cu and Cu–CH targets were reproduced for simulations with a given set of electron parameters. Comparison of the simulations revealed that the hard x-ray emission from the Cu target was significantly longer in duration than that from the Cu–CH target. The benchmarked hybrid PIC code could prove to be a powerful tool in the design and optimization of time- and angular-dependent bremsstrahlung sources for flash x-ray and gamma-ray radiography.
  Citation: Physics of Plasmas
  PubDate: 2022-09-13T01:43:53Z
  DOI: 10.1063/5.0089464
The envelope soliton for the nonlinear interaction of Langmuir waves with
electron acoustic waves in the Earth's inner magnetosphere
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  Authors: Yong Liu, Jiang Zhou
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The nonlinear coupling of Langmuir waves with electron-acoustic waves is investigated using the kinetic theory, where the hot electron component is modeled by the kappa distribution with an exponential cutoff at high energy tail, i.e., the cutoff kappa distribution. The one dimensional structure of envelope Langmuir solitons is analyzed by the numerical calculation with parameters typical of the Earth's inner magnetosphere. In the case of hot electrons with a cutoff kappa distribution, envelope Langmuir solitons have larger width and slower speed than that in the case of hot electrons with a Maxwellian distribution. The envelop Langmuir soliton with density depletion obtained in the Earth's inner magnetosphere propagates at a speed lower than the electron-acoustic velocity. At a given amplitude of electrostatic field, the envelope Langmuir soltions have a speed comparable with the ones of electron-acoustic wave solitons, but a wider scale in the case of hot electrons with a cutoff kappa distribution.
  Citation: Physics of Plasmas
  PubDate: 2022-09-13T01:42:53Z
  DOI: 10.1063/5.0096999
Research on the spatio-temporal characteristics of high energy pulsed
plasma jets
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  Authors: Pengfei Zhang, Xin Liu, Mengjiao Lin, Jia Zhang
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  This research proposes a high-energy pulsed plasma jet for producing highly dynamic and huge gradient plasma. The injected plasma enters the plasma sheath, and the stealth of the high-speed vehicle is achieved by modulating the dynamics of the plasma sheath electron density. The characteristics of the plasma were extensively diagnosed using current–voltage measurements, high-speed cameras, and optical emission spectroscopy. This includes the electrical parameters of the plasma and its spatial and temporal distribution. The deposited energy rises and then falls as the pressure rises. The high-speed camera determines that the plasma injection process lasted 160.04 μs. The electron temperature ranges from 0.68 to 1 eV. The electron density ranges from 2.5 × 1016 to 2.1 × 1017 cm−3 with an increasing trend from 0 to 12 μs and a decreasing trend from 12 to 28 μs. As the axial position rises, the electron density gradually decays. The analysis of high-energy pulsed plasma jets provides the framework for future research into active stealth in high-speed vehicles.
  Citation: Physics of Plasmas
  PubDate: 2022-09-12T09:42:00Z
  DOI: 10.1063/5.0098307
Indirect energy transfer channel between fast ions via nuclear elastic
scattering observed on the large helical device
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  Authors: H. Matsuura, K. Kimura, D. Umezaki, K. Ogawa, M. Isobe, Y. Kawamoto, T. Oishi, M. Goto, N. Tamura, M. Osakabe, T. Nishitani, S. Sugiyama
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  An energy transfer phenomenon between energetic ions, which cannot be explained only considering the Coulomb scattering process, was observed on a large helical device (LHD). This phenomenon often occurs in fusion reactivity enhancement and fast-ion slowing-down process that can be observed as a delay in the decay time of the D(d,n)3He neutron generation rate. The transferred energy required to induce such a reactivity enhancement or delay in the fast-ion slowing-down time (neutron decay time) was examined based on the Boltzmann−Fokker−Planck analysis in which a discrete energy transfer process, called nuclear elastic scattering (NES), is included. It was shown that even though the cross section of the NES is smaller than that of the Coulomb scattering, enough knock-on population appears in the energetic region in ion distribution function to induce the observable NES effects; thus, enough energy is transferred from beam ions to fast component of bulk ion distribution function indirectly and the transferred energy per unit time via NES is comparable to the Coulomb scattering rate. This study analytically demonstrates that the observed phenomena on LHD can be explained smoothly by considering the alternative indirect energy transfer channel between energetic ions, which can be comparable with the one via Coulomb scattering.
  Citation: Physics of Plasmas
  PubDate: 2022-09-12T09:41:59Z
  DOI: 10.1063/5.0097720
Experimental investigation on the hysteresis in low-pressure inductively
coupled neon discharge
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  Authors: Young-Hun Hong, Tae-Woo Kim, Ju-Ho Kim, Yeong-Min Lim, Moo-Young Lee, Chin-Wook Chung
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  A hysteresis phenomenon observed in neon inductive discharge at low gas pressure is investigated in terms of the evolution of the electron energy distribution function (EEDF). Generally, the hysteresis phenomenon has been reported at high-pressure Ramsauer gas discharges. However, in neon plasma, we found that the hysteresis phenomenon occurs even at low gas pressure (5 mTorr). Furthermore, the hysteresis vanishes with an increase in the gas pressure (10 and 25 mTorr). To analyze this hysteresis, the EEDF is measured depending on the radio frequency power. The EEDF at 10 mTorr sustains the bi-Maxwellian distribution during an E–H transition. On the other hand, the EEDF at 5 mTorr changes dramatically between discharge modes. At 5 mTorr, the measured EEDF for the E mode has the Maxwellian distribution due to high collisional heating in the bulk plasma. The EEDF for the H mode has the bi-Maxwellian distribution because collisionless heating in the skin depth is dominant. This apparent evolution of the EEDF causes a nonlinear energy loss due to collisions during the discharge mode transition. Therefore, the plasma can maintain the H mode discharge with high ionization efficiency, even at a lower applied power, which results in the hysteresis.
  Citation: Physics of Plasmas
  PubDate: 2022-09-12T09:41:55Z
  DOI: 10.1063/5.0092091
Study on Townsend first ionization coefficient in a streamer filament of
the pulsed electric discharge in water
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  Authors: Yuantian Yang, Xiaoqiong Wen, Liru Wang, Xue Wang
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Streamers in water usually consist of several weakly ionized gaseous filaments. It is important to understand the ionization and excitation processes occurring in a streamer filament. In this paper, we studied the Townsend first ionization coefficient α in a streamer filament. The emission images of streamers in water were acquired by using an ultra-high speed camera system. Based on the emission images, it was found that the luminance of a streamer filament decreased exponentially as the distance increased from the anode tip. The Townsend first ionization coefficient in the streamer filament in water was then estimated by the emission profile method. It was found that the Townsend first ionization coefficient in a streamer filament was 5.3 cm−1 on average and did not depend on the water conductivity or the applied voltage of interest in the present paper. The Townsend first ionization coefficient estimated by the emission profile method is in agreement with that deduced from the electron density profile of the streamer filament in water, indicating that the emission profile method for measuring the Townsend first ionization coefficient can be applicable to the streamers in water. We also estimated the reduced Townsend first ionization coefficient α/N in a streamer filament in water and found that the obtained value for α/N was four orders of magnitude lower than those obtained from the glow discharge in low pressure water vapor, but at least ten orders of magnitude greater than those predicted by the empirical formulas.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T12:07:22Z
  DOI: 10.1063/5.0099396
Multi-harmonic Rutherford island theory
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  Authors: R. Fitzpatrick
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Rutherford island theory, which governs the nonlinear evolution of tearing modes in tokamak plasmas, is generalized to take into account situations in which the conventional one-harmonic approximation is not valid. The analysis incorporates non-inductive currents driven by radio frequency (RF) electromagnetic waves injected into the plasma. A multi-harmonic tearing mode dispersion relation is derived that takes the form of a nonlinear inhomogeneous matrix eigenvalue problem. The dispersion relation is solved in the so-called two-harmonic approximation, in which only the principal Fourier harmonic of the perturbed magnetic flux and its first overtone are included in the calculation. In the absence of RF current drive, the nonlinear behavior of a tearing mode predicted in the two-harmonic approximation does not differ substantially from that predicted in the one-harmonic approximation. On the other hand, RF current drive that is sufficiently localized in the vicinity of the O-points of the mode's magnetic island chain is capable of triggering bifurcations of the O-points (which is impossible in the one-harmonic approximation). However, the current drive is incapable of triggering bifurcations of the island X-points. This finding is significant because Bardóczi and Evans [Phys. Rev. Lett. 126, 085003 (2021)] recently observed bifurcations of magnetic island chain O-points in the presence of RF current drive in the DIII-D tokamak but did not observe bifurcations of the X-points. Finally, the changes in the topology of the magnetic island flux-surfaces induced by RF current drive are found to facilitate the stabilization of the tearing mode.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T12:07:20Z
  DOI: 10.1063/5.0099489
Discharge in a long metal tube with an electron beam generated by a
forevacuum plasma–cathode electron source
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  Authors: V. A. Burdovitsin, K. I. Karpov, I. Yu. Bakeev, E. M. Oks
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  We describe our investigations of the current distribution in a non-self-sustained hollow-cathode glow discharge in a long metal tube. The discharge is initiated and sustained by injecting an electron beam generated by a forevacuum-pressure plasma–cathode electron source into the tube. It is shown that the distribution of discharge current along the inner sidewall over the tube length and, correspondingly, the distribution of plasma density along the tube depend primarily on tube geometry and electron beam current. The character of the discharge current distribution is determined by the ratio of contributions to ionization by beam electrons and by secondary electrons emitted from the tube bottom (if the lower end of the tube is closed) and from the tube sidewall. These processes may lead to a non-monotonic distribution of discharge current with a minimum in the middle. Increasing the discharge current levels out this minimum, improving the uniformity of the current distribution over the tube length.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T12:07:19Z
  DOI: 10.1063/5.0100290
Experimental investigation on the evolution of vacuum arc in the quench
protection switch based on forced current zero
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  Authors: Zongqian Shi, Xinkun Lv, Jing Guo, Sheng Li, Yongpeng Mo, Jiajia Sun
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  In this paper, the evolution of vacuum arc under different conditions in the quench protection switch (QPS) based on forced current zero was investigated experimentally and analyzed quantitatively. Experiments were conducted with cup-shaped axial magnetic field (AMF) contacts in a demountable vacuum chamber. Images of the arc column were photographed through the observation window with a high-speed digital camera with exposure time of 2 μs. Arc appearance was analyzed quantitatively through digital image processing. Quantified arc appearance and arc voltage characteristics indicated that the high-current vacuum arc evolution in the QPS could be divided into four stages: arc formation stage, arc column merging stage, diffusing stage, and fast extinguishing stage. The influence of AMF on the evolution of high-current vacuum arc in the diffusing stage was also studied. Experiment results indicated that the vacuum arc at relatively low current had a simpler evolution process and the arc column merging had less correlation with voltage stability. It was found that the vacuum arc with a long gap distance developed faster and the time required to enter the stable burning state was shorter. In addition, the vacuum arc with long arcing time tended to constrict again, which is not beneficial to current interruption.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T12:07:19Z
  DOI: 10.1063/5.0098731
Dynamics of plasmas produced by a laser pulse, inside a dense gaseous
target, formed in an ambient gas
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  Authors: Andrzej Bartnik, Karol Jach, Robert Świerczyński, Mateusz Majszyk, Tomasz Fok, Łukasz Węgrzyński, Przemysław Wachulak, Henryk Fiedorowicz
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  In this work, the time development of plasmas produced by interaction of laser pulses, with a nitrogen gas, was investigated. The interaction took place inside a small portion of dense nitrogen gas injected temporarily into a chamber filled with the gas under low pressure. High-temperature plasmas produced directly by the laser pulse were a source of soft x rays and charged particles, ionizing and exciting the surrounding gas. In this way, low-temperature plasmas were produced. The formation of high-temperature plasmas was studied using soft x-ray spectroscopy and x-ray streak imaging. Low-temperature plasmas formed at various distances from the laser focus were investigated using an optical streak camera. Interpretation of the experimental data was supported by numerical modeling of the laser-produced plasma hydrodynamics. It was concluded that depending on the distance from the focal spot, the formation of the low-temperature plasmas was dominated by ion streams or by soft x-ray radiation.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T12:07:17Z
  DOI: 10.1063/5.0099683
Simulated experiments for removal of odorous gases by wire-mesh electrode
dielectric barrier discharge
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  Authors: Geon W. Yang, Se M. Chun, Kang I. Kim, Hee J. Lee, Yongcheol Hong
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  The emission of odorous gases from various industrial processes such as factories and wastewater treatment, in addition to emissions from landfills and livestock, has become a public concern because of their negative effect on air quality and human health. This study presents a technology based on dielectric barrier discharge (DBD) of wire-mesh type with a high-voltage electric wire as the electrode. This system was used to experimentally assess the removal efficiency of odorous gases. The plasma system consists of a wire electrode with a mesh-type configuration, a small blower (1.6 N m3/min, compressed air) for the plasma discharge or to supply cooling gas, and an AC high-voltage power supply. The plasma system offers the advantages of low power consumption and a large discharge area for ozone production. The wire-mesh electrode DBD comprises 64 discharge nodes, and the large amount of ozone generated from these nodes is used to oxidize odorous gases. Under optimized conditions, ozone is stably generated at the rate of 5.1 g/h for a specific input energy of 3.7 J/L. The ozone and odorous compounds (H2S: 4.5 ppm, CH3SH: 6.7 ppm, NH3: 3 ppm, outlet concentration) are injected into the main blower (20 N m3/min, compressed air). Finally, the experiments designed to simulate the removal of odorous gases confirmed that 99% of odorous compounds were removed using the wire-mesh electrode DBD. The cost-effectiveness and scalability of this system make it highly suitable for use in industrial environments where odorous gases are produced.
  Citation: Physics of Plasmas
  PubDate: 2022-09-09T11:27:17Z
  DOI: 10.1063/5.0097519
Dust particle surface potential in fusion plasma with supra-thermal
electrons
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  Authors: J. M. Long, Jing Ou
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  By solving the current balance equations, the effect of the supra-thermal electrons on the surface potential of a negatively charged dust particle in a fusion plasma is studied based on the orbital motion limited theory. A non-Maxwellian plasma is modeled by employing a q-non-extensive velocity distribution, where a decreased q-parameter (q
  Citation: Physics of Plasmas
  PubDate: 2022-09-06T10:07:11Z
  DOI: 10.1063/5.0091856
Near-cancellation of up- and down-gradient momentum transport in forced
magnetized shear-flow turbulence
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  Authors: B. Tripathi, A. E. Fraser, P. W. Terry, E. G. Zweibel, M. J. Pueschel
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Visco-resistive magnetohydrodynamic turbulence, driven by a two-dimensional unstable shear layer that is maintained by an imposed body force, is examined by decomposing it into dissipationless linear eigenmodes of the initial profiles. The down-gradient momentum flux, as expected, originates from the large-scale instability. However, continual up-gradient momentum transport by large-scale linearly stable but nonlinearly excited eigenmodes is identified and found to nearly cancel the down-gradient transport by unstable modes. The stable modes effectuate this by depleting the large-scale turbulent fluctuations via energy transfer to the mean flow. This establishes a physical mechanism underlying the long-known observation that coherent vortices formed from nonlinear saturation of the instability reduce turbulent transport and fluctuations, as such vortices are composed of both the stable and unstable modes, which are nearly equal in their amplitudes. The impact of magnetic fields on the nonlinearly excited stable modes is then quantified. Even when imposing a strong magnetic field that almost completely suppresses the instability, the up-gradient transport by the stable modes is at least two-thirds of the down-gradient transport by the unstable modes, whereas for weaker fields, this fraction reaches up to 98%. These effects are persistent with variations in magnetic Prandtl number and forcing strength. Finally, continuum modes are shown to be energetically less important, but essential for capturing the magnetic fluctuations and Maxwell stress. A simple analytical scaling law is derived for their saturated turbulent amplitudes. It predicts the falloff rate as the inverse of the Fourier wavenumber, a property which is confirmed in numerical simulations.
  Citation: Physics of Plasmas
  PubDate: 2022-09-02T10:35:00Z
  DOI: 10.1063/5.0101434
Kinetic theory of nonrelativistic electron beam–inhomogeneous plasma
system instability
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  Authors: Vladimir S. Sukhomlinov, Alexander S. Mustafaev, Hend Koubaji, Nikolai A. Timofeev, Oscar Gabriel Murillo Hiller, Georges Zissis
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  On the basis of kinetic theory, the stability of an electron beam interacting with inhomogeneous plasma is investigated at Knudsen numbers of the order of 1. The theory has been tested on the example of a low-voltage beam discharge in a rear gas. It is shown that in the case of an inhomogeneous plasma even if the attenuation of a beam is neglected, several perturbations can propagate simultaneously at the same frequency, but with different phase and group velocities and increments. The case of a linear dependence of the plasma density on the coordinate is investigated in detail. In this case, there are two solutions: n- and p-waves, only the n-wave having a physical meaning. It is found that an increase in the plasma density gradient leads to a decrease in the increment and an increase in the phase and group velocities of propagation of perturbations with a frequency of the order of plasma frequency. A system with a growing plasma density along the beam direction is more stable than that with a constant density. For a significant change in the growth rate of the disturbance, the relative gradient of plasma density by an amount of about 10% at the wavelength is sufficient. All the observed features of the perturbation parameters depending on the plasma density gradient are physically interpreted. The calculations are confirmed by experimental data.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:15:09Z
  DOI: 10.1063/5.0097263
Detailed investigation on x-ray emission from laser-driven high-Z foils in
a wide intensity range: Role of conversion layer and re-emission zone
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  Authors: Gaurav Mishra, Karabi Ghosh
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Detailed radiation hydrodynamic simulations are carried out to investigate the x-ray emission process in four high-Z planar targets, namely, tungsten (W), gold (Au), lead (Pb), and uranium (U) irradiated by 1 ns, 351 nm flat top laser pulses. A thorough zoning analysis is performed for all laser-driven high-Z foils over a wide intensity range of [math] W/cm2 with appropriately chosen photon energy range and recombination parameter. The resulting variation of conversion efficiency over the full intensity range exhibits an optimum for all materials, which is explained by considering the characteristic emission contributions from two different regions of laser irradiated plasma, namely, conversion layer and re-emission zone. A new generalized single scaling relation based upon smooth broken power law is proposed for conversion efficiency variation along with the separate determination (ηS, ηM) in soft and hard/M-band x-ray regions. It has been observed that ηS for Pb and W always lies in between that for Au and U for intensities smaller than [math] W/cm2. On further increase in intensity, ηS is observed to be maximum for Au and U, whereas it is minimum for W. Significant contribution to M-band conversion efficiencies is observed in all elements for intensities higher than [math] W/cm2 with maximum and minimum values attained by W and U, respectively. The results are explained by considering the contributions from the emission coefficients of all materials in both conversion layer and re-emission zone up to corresponding photon cutoff energies at different laser intensities.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:15:04Z
  DOI: 10.1063/5.0091996
An X-band high-power and high-efficiency coaxial relativistic klystron
oscillator with four-gap buncher and three-gap extractor
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  Authors: Peng Zhang, Fangchao Dang, Xingjun Ge, Ting Shu, Xiaodong Hu, Hang Chi, Juntao He
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Because of the scaling invariance, the over-mode ratio of the coaxial resonator can be increased to increase the power handling capability. However, as the over-mode ratio increases, the characteristic impedance and external quality factor decrease, which causes the modulation of the electron beam to be weakened. Moreover, when the output microwave power increases, the double-gap output cavity will suffer from severe radio frequency breakdown. Therefore, an X-band high-power and high-efficiency coaxial relativistic klystron oscillator with a four-gap modulation cavity and a three-gap extraction cavity is proposed. First, a four-gap modulation cavity can increase the modulation depth of the electron beam to improve the beam-wave conversion efficiency. The operating mode of the modulation cavity is the 3π/4 mode of the coaxial TM01 mode. Second, a three-gap extraction cavity is adopted to enhance the microwave extraction energy and reduce the RF field strength. The simulation results show that when the diode voltage is 650 kV, the beam current is 15.4 kA, and the guiding magnetic field is 0.48 T, the device outputs a microwave power of 4.2 GW, a frequency of 8.4 GHz, and an efficiency of 42%.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:13:43Z
  DOI: 10.1063/5.0101188
High-frequency radio-wave emission by coherent transition radiation of
runaway electrons produced by lightning stepped leaders
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  Authors: L. Guo, H.-W. Zhang, H.-C. Wu
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Lightning can produce multiband radio waves and high-energy radiations. Some of them are associated with the formation of lightning leaders. However, their generation mechanisms are not fully understood yet. Based on the understanding of thermal runaway electrons generated at the leader tip, we propose transition radiation of these runaway electrons as an alternative mechanism for producing very-high-frequency radio signals. Transition radiations are induced when runaway electrons cross the interfaces between lightning coronas and the air. By the use of estimated parameters of electron beams emerging from the leader tips, we calculate their coherent transition radiation and find that the energy spectra and radiation powers are consistent with some detection results from stepped leaders and even narrow bipolar events. Moreover, our model also predicts strong THz radiation during the stepped-leader formation. As a standard diagnosis technique of electron bunches, the proposed coherent transition radiation here may be able to reconstruct the actual properties of electron beams in the leader tips, which remains an open question.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:13:42Z
  DOI: 10.1063/5.0102132
Relativistic atomic structure calculations of KIX with plasma parameters
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  Authors: Richa Paijwar, Rinku Sharma, Alok K. Singh Jha
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Systematic calculations for energy levels, lifetimes, and radiative data for the KIX are reported, including oscillator strengths, transition wavelengths, line strengths, and radiative rates of electric dipole (E1) transition, electric quadrupole (E2) transition, magnetic dipole (M1) transition, and magnetic quadrupole (M2) transition, using GRASP. Quantum electrodynamics and Breit correction have been considered in our calculations. The importance and effect of valence valence and core valence correlations on the excitation energies have been discussed in graphical and tabular forms. Analogous calculations using flexible atomic code (FAC) and the large-scale configuration interaction technique have also been done to confirm the accuracy of energy levels. The calculated results are in close agreement with NIST compiled data and other available results. The influence of plasma temperature (2 × 106–1 × 1010 K) on the line intensity ratio with the number of electron density has been studied for the hot dense plasma (HDP) graph for KIX. Our reported results will be valuable or beneficial for the characterization of HDP, astrophysical plasmas, and plasma modeling.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:06:03Z
  DOI: 10.1063/5.0095476
Collisions of proton or highly charged ion–atom in a strong magnetic
field and dense quantum plasmas
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  Authors: Guozhuang Li, Sheng Zhang, Zhihong Jiao, Qiang Yan, Xinxia Li
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  Magneto inertial fusion driven by heavy ions beam (HIB) is a very attractive potential approach for the nuclear energy system. One of the key issues is to investigate the interaction process of the HIB-target considering the condition of plasma screening and strong magnetic field background. In this paper, the influence of the external magnetic field and the plasma screening was investigated by simplifying the process of beam bombarding into a two-body collision between the energetic ions and target atoms. The classical-trajectory Monte Carlo method was accommodated by modifying the Hamiltonian in the collision system, where the effects of plasma screening and the account for the strong magnetic field background were considered. The total cross sections of single electron ionization and charge transfer of the projectile (H+, He2+, Xe32+, Bi31+, U34+)–atom (H, He) collisions are computed. The results indicated that the magnetic field effect becomes more obvious in the low energy regime of the projectiles. With the increase in energy, the change of total cross sections and angular differential cross sections gradually disappears. In the dense quantum plasmas, plasma screening presents very different effects for protons and heavy ion projectiles. This work may pave the way for extending the study to other collision systems calculations.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T11:06:01Z
  DOI: 10.1063/5.0090775
Chapman–Enskog derivation of multicomponent Navier–Stokes
equations
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  Authors: Philippe Arnault, Sébastien Guisset
  Abstract: Physics of Plasmas, Volume 29, Issue 9, September 2022.
  There are several reasons to extend the presentation of Navier–Stokes equations to multicomponent systems. Many technological applications are based on physical phenomena that are present in neither pure elements nor in binary mixtures. Whereas Fourier's law must already be generalized in binaries, it is only with more than two components that Fick's law breaks down in its simple form. The emergence of dissipative phenomena also affects the inertial confinement fusion configurations, designed as prototypes for the future fusion nuclear plants hopefully replacing the fission ones. This important topic can be described in much simpler terms than it is in many textbooks since the publication of the formalism put forward recently by Snider [Phys. Rev. E 82, 051201 (2010)]. In a very natural way, it replaces the linearly dependent atomic fractions by the independent set of partial densities. Then, the Chapman–Enskog procedure is hardly more complicated for multicomponent mixtures than for pure elements. Moreover, the recent proposal of a convergent kinetic equation by Baalrud and Daligault [Phys. Plasmas 26, 082106 (2019)] demonstrates that the Boltzmann equation with the potential of mean force is a far better choice in situations close to equilibrium, as described by the Navier–Stokes equations, than Landau or Lenard–Balescu equations. In our comprehensive presentation, we emphasize the physical arguments behind Chapman–Enskog derivation and keep the mathematics as simple as possible. This excludes, as a technical non-essential aspect, the solution of the linearized Boltzmann equation through an expansion in Hermite polynomials. We discuss the link with the second principle of thermodynamics of entropy increase, and what can be learned from this exposition.
  Citation: Physics of Plasmas
  PubDate: 2022-09-01T05:57:43Z
  DOI: 10.1063/5.0088013