Ion-acoustic shocks with reflected ions: modelling and particle-in-cell simulations

Liseykina, T. V.; Dudnikova, G. I.; Вшивков, В. А.; Malkov, Mikhail

doi:10.1017/s002237781500077x

Cited by 13 publications

(23 citation statements)

References 25 publications

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“…We further highlight the following findings of this paper: Based on the numerous PIC simulations, available in the literature (e.g., [9,10,41]), we may speculate that when the Mach number exceeds its critical value M 2 , obtained in this paper, the shock evolution becomes time dependent; ions reflect intermittently. One example of such dynamics, Fig.5, we adopted from the recent PIC simulations [41] (see also Appendix for a further brief discussion of this result). For yet higher Mach numbers, the upstream and downstream flows do not couple together, but rather penetrate through each other, not being perturbed significantly.…”

Section: Discussionsupporting

confidence: 67%

“…As the beam "hydrodynamics" is truly collisionless, their intersection will result in a multi-flow state of the reflected beam. Such states copiously emerge in simulations, e.g., [10,41,42], along with…”

Section: Discussionmentioning

confidence: 94%

“…Numerical treatments, however, included finite ion temperature and have been able to address the effect of ion reflection on the shock structure by using PIC simulations, e.g. [10,41]. The ion reflection alters the shock amplitude and speed, thus impacting the reflection threshold itself.…”

Section: Discussionmentioning

confidence: 99%

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Ion-acoustic shocks with self-regulated ion reflection and acceleration

et al. 2016

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An analytic solution describing an ion-acoustic collisionless shock, self-consistently with the evolution of shock-reflected ions, is obtained. The solution extends the classic soliton solution beyond a critical Mach number, where the soliton ceases to exist because of the upstream ion reflection. The reflection transforms the soliton into a shock with a trailing wave and a foot populated by the reflected ions. The solution relates parameters of the entire shock structure, such as the maximum and minimum of the potential in the trailing wave, the height of the foot, as well as the shock Mach number, to the number of reflected ions. This relation is resolvable for any given distribution of the upstream ions. In this paper, we have resolved it for a simple "box" distribution. Two separate models of electron interaction with the shock are considered. The first model corresponds to the standard Boltzmannian electron distribution in which case the critical shock Mach number only insignificantly increases from M ≈ 1.6 (no ion reflection) to M ≈ 1.8 (substantial reflection).The second model corresponds to adiabatically trapped electrons. They produce a stronger increase, from M ≈ 3.1 to M ≈ 4.5. The shock foot that is supported by the reflected ions also accelerates them somewhat further. A self-similar foot expansion into the upstream medium is also described analytically.

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Section: Discussionsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 94%

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Ion-acoustic shocks with self-regulated ion reflection and acceleration

et al. 2016

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“…It is more important than possible shock rippling effects, not captured by 1D simulations. Besides that, shock rippling and its impact on particle reflection cannot be accurately characterized within hybrid simulations and require a full kinetic treatment (Liseykina et al 2015;Malkov et al 2016;Malkov 2017). For the reasons explained in detail in sections 4.2 and 4.3 we deliberately choose the 1D treatment as a first step in a systematic study of the A/Z dependence of injection efficiency.…”

Section: Simulation Set-upmentioning

confidence: 99%

Acceleration of Cosmic Rays in Supernova Shocks: Elemental Selectivity of the Injection Mechanism

Hanusch

Liseykina

Malkov

2019

ApJ

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Precise measurements of galactic cosmic rays revealed a significant difference between the rigidity spectral indices of protons and helium ions. This finding is a notable contrast to the commonly accepted theoretical prediction that supernova remnant (SNR) shocks accelerate protons and helium ions with the same rigidity alike. Most of the earlier explanations for the "paradox" appealed to SNR environmental factors, such as inhomogeneous p/He mixes in the shock upstream medium, variable ionization states of He, or a multi-SNR origin of the observed spectra. The newest observations, however, are in tension with most of them. In this paper, we show by self-consistent hybrid simulations that such special conditions are not vital for the explanation of the cosmic ray rigidity spectra. In particular, our simulations prove that an SNR shock can modify the chemical composition of accelerated cosmic rays by preferentially extracting them from a homogeneous background plasma without additional, largely untestable assumptions. Our results confirm the earlier theoretical predictions of how the efficiency of injection depends on the shock Mach number M. Its increase with the charge-to-mass ratio saturates at a level that grows with M. We have convolved the time-dependent injection rates of protons and helium ions, obtained from the simulations, with a decreasing shock strength over the active life of SNRs. The integrated SNR rigidity spectrum for p/He ratio compares well with the AMS-02 and PAMELA data.

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“…Onedimensional PIC simulations [12] have examined the interaction of a hot pair cloud that expands into an ambient plasma. The simulations have shown that electron phase space holes [13][14][15][16], which form and evolve on electron time scales, and the ion acoustic solitary waves that are tied to them [17] could be an efficient means to accelerate ions to high energies especially when the ion acoustic solitary waves break [18]. Our aim is to study these processes in more detail with a two-dimensional particlein-cell (PIC) simulation that resolves competing multidimensional instabilities such as those that destroy phase space holes in more than one dimension [13].…”

Section: Introductionmentioning

confidence: 99%

Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma

2018

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The expansion of a charge-neutral cloud of electrons and positrons with the temperature 1 MeV into an unmagnetized ambient plasma is examined with a 2D particle-in-cell (PIC) simulation. The pair outflow drives solitary waves in the ambient protons. Their bipolar electric fields attract electrons of the outflowing pair cloud and repel positrons. These fields can reflect some of the protons thereby accelerating them to almost an MeV. Ion acoustic solitary waves are thus an efficient means to couple energy from the pair cloud to protons. The scattering of the electrons and positrons by the electric field slows down their expansion to a nonrelativistic speed. Only a dilute pair outflow reaches the expansion speed expected from the cloud's thermal speed. Its positrons are more energetic than its electrons. In time an instability grows at the front of the dense slow-moving part of the pair cloud, which magnetizes the plasma. The instability is driven by the interaction of the outflowing positrons with the protons. These results shed light on how magnetic fields are created and ions are accelerated in pair-loaded astrophysical jets and winds.

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Ion-acoustic shocks with reflected ions: modelling and particle-in-cell simulations

Cited by 13 publications

References 25 publications

Ion-acoustic shocks with self-regulated ion reflection and acceleration

Ion-acoustic shocks with self-regulated ion reflection and acceleration

Acceleration of Cosmic Rays in Supernova Shocks: Elemental Selectivity of the Injection Mechanism

Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma

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