Ultrarelativistic particle acceleration in collisionless shock waves

Ohsawa, Yukiharu

doi:10.1016/j.physrep.2013.11.004

Cited by 16 publications

(30 citation statements)

References 139 publications

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“…The transverse electric field (plotted against the right vertical axis) scales roughly as 3.3(B − 1) for 1.8 ≤t ≤ 2.2. Finally, the amplitude of the potential jump fits quite well to the theoretical value ϕ w = 2m p v A 2 (M w − 1)/e, with M w = (1 +B m )/2 the Mach number of the pulse (here M w ∼ 1.25, 1.6 and 2 fort = 1.58, 1.87 and 2.16), obtained for a non-linear magnetosonic pulse [6,42,44].…”

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confidence: 79%

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Role of Magnetosonic Solitons in Perpendicular Collisionless Shock Reformation

2017

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The nature of the magnetic structure arising from ion specular reflection in shock compression studies is examined by means of 1d particle in cell simulations. Propagation speed, field profiles and supporting currents for this magnetic structure are shown to be consistent with a magnetosonic soliton. Coincidentally, this structure and its evolution are typical of foot structures observed in perpendicular shock reformation. To reconcile these two observations, we propose, for the first time, that shock reformation can be explained as the result of the formation, growth and subsequent transition to a super-critical shock of a magnetosonic soliton. This argument is further supported by the remarkable agreement found between the period of the soliton evolution cycle and classical reformation results. This new result suggests that the unique properties of solitons can be used to shed new light on the long-standing issue of shock non-stationarity and its role on particle acceleration.Introduction.-Collisionless shocks have been intensively studied since the late 1950's by virtue of of the role they are believed to play in plasma heating and charged particle acceleration (see, e. g., Refs. [1][2][3][4][5][6][7] and references therein). One of the most important features in high Mach number shocks is the specular reflection of upstream ions, which serves as an energy dissipation mechanism [8] to satisfy to shock conservation equations: ion specular reflection is paramount to both ion acceleration and shock structure.Further to its role in ion acceleration, ion specular reflection is responsible for the non-stationarity of quasiperpendicular shocks. This temporal variability has been demonstrated through numerical simulations (see, e. g., Refs [9-13]), observations [14][15][16][17] and experiments [18]. Although four different non-stationarity mechanisms have been suggested in full generality [5], the most likely candidate for explaining shock reformation in a 1-d exactly perpendicular shock (θ = 90• , with θ the angle between the upstream magnetic field and the shock normal) is the so-called self-reformation mechanism (see, e. g., Ref. [7]). This self reformation cycle can be summarized as follows. First, ions reflected by the shock form a foot ahead of the ramp. Due to the gyro-motion, these reflected ions pile up upstream of the foot at a distance slightly smaller than an ion gyro-radius ahead of the shock ramp, and create local magnetic field and density maxima there. Through a feedback mechanism, this foot then grows until it becomes as large as the initial shock ramp, effectively becoming the new ramp. Finally, this new ramp reflects incoming ions and the process repeats, with the shock advancing in a step-wise fashion. Numerical simulations suggest that the onset of this non-stationary reformation process is conditioned

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confidence: 79%

“…[1][2][3][4][5][6][7] and references therein). One of the most important features in high Mach number shocks is the specular reflection of upstream ions, which serves as an energy dissipation mechanism [8] to satisfy to shock conservation equations: ion specular reflection is paramount to both ion acceleration and shock structure.…”

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confidence: 99%

Role of Magnetosonic Solitons in Perpendicular Collisionless Shock Reformation

2017

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“…(A12)) and therefore do not strictly maintain form while propagating, it is interesting to consider how the ion displacement differs from Eqs. (17,18) in the case of a rarefaction pulse. For a rarefaction pulse, the ion motion is in the direction opposed to the pulse propagation.…”

Section: Particle Displacement Induced By a Magnetosonic Solitonmentioning

confidence: 99%

“…-In this section, it is assumed that the reflection of a soliton at the plasma vacuum-interface leads to another soliton, or, in other words, that the reflection does not change the form of the MS soliton, but only modifies its amplitude. Although rarefaction soliton solutions do not exist for transverse magnetosonic waves in cold plasma 17 , it is further assumed that a rarefaction pulse such as defined in Eq. (20) propagates with negligible change in form, i. e. as a soliton.…”

Section: Displacement After N Reflections In a Plasma Slabmentioning

confidence: 99%

Cumulative displacement induced by a magnetosonic soliton bouncing in a bounded plasma slab

2018

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The passage of a magnetosonic (MS) soliton in a cold plasma leads to the displacement of charged particles in the direction of a compressive pulse and in the opposite direction of a rarefaction pulse. In the overdense plasma limit, the displacement induced by a weakly nonlinear MS soliton is derived analytically. This result is then used to derive an asymptotic expansion for the displacement resulting from the bouncing motion of a MS soliton reflected back and forth in a vacuum-bounded cold plasma slab. Particles' displacement after the pulse energy has been lost to the vacuum region is shown to scale as the ratio of light speed to Alfvén velocity. Results for the displacement after a few MS soliton reflections are corroborated by particle-in-cell simulations.

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“…The generation of soliton in plasma and their role in formation of collisionless shock waves have attracted a significant amount of interest in recent years in a variety of contexts like astrophysics [1][2][3][4][5], solar and space physics [6,7], laboratory plasma experiments [8][9][10] etc. They play a key role in charged particle acceleration and plasma heating [4,[11][12][13][14][15][16]. In the presence of an external magnetic field, soliton propagation with magnetosonic/Alfven speed in plasma have been predicted.…”

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Excitation of KdV magnetosonic solitons in plasma in the presence of an external magnetic field

Kumar

Shukla

Verma

et al. 2019

Plasma Phys. Control. Fusion

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The interaction of laser with plasmas leads to many interesting phenomena which includes laser energy absorption, mode conversion, energetic particle generation etc. In this work, the excitation of Korteweg -de Vries (KdV) Alfven solitons in plasma is demonstrated with the help of 2-D Particle -In -Cell (PIC) simulations. For this purpose, the propagation of a pulsed CO2 (with a wavelength of 10µm ) laser normally incident on an overdense plasma target is considered in the presence of an external magnetic field. The magnitude of the external magnetic field is chosen so as to have the electrons magnetized and ions unmagnetized at the laser frequency. These solitons propagate stably and are observed to be responsible for energetic electron generation as the background undisturbed electrons of the medium get reflected from its front. It is also shown that subsequently, transverse modulations appear in the structure which grow with time. With recent technological advancements in the development of short pulse CO2 lasers and also on the generation of magnetic fields of the order of tens of kilo -Tesla in the laboratory, these studies have practical relevance and have a possibility of getting replicated in laboratory in near future.

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Ultrarelativistic particle acceleration in collisionless shock waves

Cited by 16 publications

References 139 publications

Role of Magnetosonic Solitons in Perpendicular Collisionless Shock Reformation

Role of Magnetosonic Solitons in Perpendicular Collisionless Shock Reformation

Cumulative displacement induced by a magnetosonic soliton bouncing in a bounded plasma slab

Excitation of KdV magnetosonic solitons in plasma in the presence of an external magnetic field

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