arXiv subjects

Krzysztof Stasiewicz

Publications and source records attributed to Krzysztof Stasiewicz.

8 recordsLinked to original sources

arXiv2026

Ballistic Surfing Acceleration as a Coherent Mechanism for Electron Acceleration in Galaxy Cluster Shocks

Radio relics in merging galaxy clusters are widely interpreted as synchrotron emission from relativistic electrons accelerated at large-scale shocks. However, the efficiency of diffusive shock acceleration (DSA) is expected to be suppressed in the low-Mach-number, weakly turbulent environments of cluster mergers; furthermore, recent theoretical insights suggest that DSA may not constitute a viable physical mechanism for such environments. In this work, we investigate ballistic surfing acceleration (BSA) as an electrodynamically grounded alternative for electron energization that bypasses the need for prescribed diffusion coefficients. We formulate BSA under typical cluster shock conditions, deriving the balance between coherent acceleration by the convective electric field and radiative losses from synchrotron and inverse-Compton cooling. This equilibrium defines the maximum reachable electron energy and constrains the resulting steady-state spectrum. By forward-modeling the associated synchrotron emission and comparing it with integrated radio observations of the `Sausage' (CIZA J2242.8+5301) and `Toothbrush' (1RXS J0603.3+4214) relics, we find that the observed spectral curvature and high-frequency steepening are consistent with BSA-limited energies, provided that active acceleration involves only a minute participation fraction ($10^{-9}$-$10^{-8}$) of the radiating electrons. Despite this high selectivity, BSA effectively produces Lorentz factors of $γ\sim 10^4$-$10^5$. Our results suggest that radio relics serve as prime astrophysical laboratories for probing coherent acceleration, with the BSA framework providing a robust and physically consistent explanation for electron energization in cluster shocks.

astro-ph.HE↗

arXiv2024

Reinterpretation of the Fermi acceleration of cosmic rays in terms of the ballistic surfing acceleration in supernova shocks

The applicability of first-order Fermi acceleration in explaining the cosmic ray spectrum has been reexamined using recent results on shock acceleration mechanisms from the Multiscale Magnetospheric mission in Earth's bow shock. It is demonstrated that the Fermi mechanism is a crude approximation of the ballistic surfing acceleration (BSA) mechanism. While both mechanisms yield similar expressions for the energy gain of a particle after encountering a shock once, leading to similar power-law distributions of the cosmic ray energy spectrum, the Fermi mechanism is found to be inconsistent with fundamental equations of electrodynamics. It is shown that the spectral index of cosmic rays is determined by the average magnetic field compression rather than the density compression, as in the Fermi model. It is shown that the knee observed in the spectrum at an energy of 5x10^{15} eV could correspond to ions with a gyroradius comparable to the size of shocks in supernova remnants. The BSA mechanism can accurately reproduce the observed spectral index s = -2.5 below the knee energy, as well as a steeper spectrum, s = -3, above the knee. The acceleration time up to the knee, as implied by BSA, is on the order of 300 years. First-order Fermi acceleration does not represent a physically valid mechanism and should be replaced by ballistic surfing acceleration in applications or models related to quasi-perpendicular shocks in space. It is noted that BSA, which operates outside of shocks, was previously misattributed to shock drift acceleration (SDA), which operates within shocks.

astro-ph.HE↗

arXiv2021

Local acceleration of protons to 100 keV in a quasi-parallel bow shock

Recent observations in the quasi-parallel bow shock by the MMS spacecraft show rapid heating and acceleration of ions up to an energy of about 100 keV. It is demonstrated that a prominent acceleration mechanism is the nonlinear interaction with a spectrum of waves produced by gradient driven instabilities, including the lower hybrid drift (LHD) instability, modified two-stream (MTS) instability and electron cyclotron drift (ECD) instability. Test-particle simulations show that the observed spectrum of waves can rapidly accelerate protons up to a few hundreds keV by the ExB mechanism. The ExB wave mechanism is related to the surfatron mechanism at shocks but through the coupling with the stochastic heating condition it produces significant acceleration on much shorter temporal and spatial scales by the interaction with bursts of waves within a cyclotron period. The results of this paper are built on the heritage of four-point measurement techniques developed for the Cluster mission and imply that the concepts of Fermi acceleration, diffusive shock acceleration, and shock drift acceleration are not needed to explain proton acceleration to hundreds keV at the Earth's bow shock.

physics.space-ph↗

arXiv2021

Ion acceleration to MeV by the ExB wave mechanism in collisionless shocks

It is shown that ions can be accelerated to MeV energy range in the direction perpendicular to the magnetic field by the ExB mechanism of electrostatic waves. The acceleration occurs in discrete steps of duration being a small fraction the gyroperiod and can explain observations of ion energization to 10 keV at quasi-perpendicular shocks and to 100-1000 keV at quasi-parallel shocks. A general expression is provided for the maximum energy of ions accelerated in shocks of arbitrary configuration. The waves involved in the acceleration are related to three cross-field current-driven instabilities: the lower hybrid drift (LHD) instability induced by the density gradients in shocks and shocklets, followed by the modified two-stream (MTS) and electron cyclotron drift (ECD) instabilities, induced by the ExB drift of electrons in the strong LHD wave electric field. The ExB wave mechanism accelerates heavy ions to energies proportional to the atomic mass number, which is consistent with satellite observations upstream of the bow shock and also with observations of post-shocks in supernovae remnants.

physics.space-ph↗

arXiv2020

Stochastic and quasi-adiabatic electron heating in quasi-parallel shocks

Using Magnetospheric Multiscale (MMS) observations at the Earth's quasi-parallel bow shock we demonstrate that electrons are heated by two different mechanisms: a quasi-adiabatic heating process during magnetic field compression, characterized by the isotropic temperature relation $T/B=(T_0/B_0)(B_0/B)^α$ with $α=2/3$ when the electron heating function $|χ_e|<1$, and a stochastic heating process when $|χ_e|>1$. Both processes are controlled by the value of the stochastic heating function $χ_j = m_j q_j^{-1} B^{-2}\mathrm{div}(\mathbf{E}_\perp)$ for particles with mass $m_j$ and charge $q_j$ in the electric and magnetic fields $\mathbf{E}$ and $\mathbf{B}$. Test particle simulations are used to show that the stochastic electron heating and acceleration in the studied shock is accomplished by waves at frequencies (0.4 - 5) $f_{ce}$ (electron gyrofrequency) for bulk heating, and waves $f>5\,f_{ce}$ for acceleration of the tail of the distribution function. Stochastic heating can give rise to flat-top electron distribution functions, frequently observed near shocks. It is also shown that obliquely polarized electric fields of electron cyclotron drift (ECD) and ion acoustic instabilities scatter the electrons into the parallel direction and keep the isotropy of the electron distribution. The results reported in this paper may be relevant to electron heating and acceleration at interplanetary shocks and other astrophysical shocks.

physics.space-ph↗

arXiv2020

Quasi-adiabatic and stochastic heating and particle acceleration at quasi-perpendicular shocks

Based on Magnetospheric Multiscale (MMS) observations from the Earth's bow shock, we have identified two plasma heating processes that operate at quasi-perpendicular shocks. Ions are subject to stochastic heating in a process controlled by the heating function $χ_j = m_j q_j^{-1} B^{-2}\mathrm{div}(\mathbf{E}_\perp)$ for particles with mass $m_j$ and charge $q_j$ in the electric and magnetic fields $\mathbf{E}$ and $\mathbf{B}$. Test particle simulations are employed to identify the parameter ranges for bulk heating and stochastic acceleration of particles in the tail of the distribution function. The simulation results are used to show that ion heating and acceleration in the studied bow shock crossings is accomplished by waves at frequencies (1-10)$f_{cp}$ (proton gyrofrequency) for the bulk heating, and $f>10f_{cp}$ for the tail acceleration. When electrons are not in the stochastic heating regime, $|χ_e|<1$, they undergo a quasi-adiabatic heating process characterized by the isotropic temperature relation $T/B=(T_0/B_0)(B_0/B)^{1/3}$. This is obtained when the energy gain from the conservation of the magnetic moment is redistributed to the parallel energy component through the scattering by waves. The results reported in this paper may also be applicable to particle heating and acceleration at astrophysical shocks.

physics.space-ph↗

arXiv2020

Stochastic ion and electron heating on drift instabilities at the bow shock

The analysis of the wave content inside a perpendicular bow shock indicates that heating of ions is related to the Lower-Hybrid-Drift (LHD) instability, and heating of electrons to the Electron-Cyclotron-Drift (ECD) instability. Both processes represent stochastic acceleration caused by the electric field gradients on the electron gyroradius scales, produced by the two instabilities. Stochastic heating is a single particle mechanism where large gradients break adiabatic invariants and expose particles to direct acceleration by the DC- and wave-fields. The acceleration is controlled by function $χ= m_iq_i^{-1} B^{-2}$div($\mathbf{E}$), which represents a general diagnostic tool for processes of energy transfer between electromagnetic fields and particles, and the measure of the local charge non-neutrality. The identification was made with multipoint measurements obtained from the Magnetospheric Multiscale spacecraft (MMS). The source for the LHD instability is the diamagnetic drift of ions, and for the ECD instability the source is ExB drift of electrons. The conclusions are supported by laboratory diagnostics of the ECD instability in Hall ion thrusters.

physics.space-ph↗

arXiv2016

Multidimensional Hall magnetohydrodynamics with isotropic or anisotropic thermal pressure: numerical scheme and its validation using solitary waves

We present a numerical solver for plasma dynamics simulations in Hall magnetohydrodynamic (HMHD) approximation in one, two and three dimensions. We consider both isotropic and anisotropic thermal pressure cases, where a general gyrotropic approximation is used. Both explicit energy conservation equation and general polytropic state equations are considered. The numerical scheme incorporates second-order Runge-Kutta advancing in time and Kurganov-Tadmor scheme with van Leer flux limiter for the approximation of fluxes. A flux-interpolated constrained-transport approach is used to preserve solenoidal magnetic field in the simulations. The implemented code is validated using several test problems previously described in the literature. Additionally, we propose a new validation method for HMHD codes based on solitary waves that provides a possibility of quantitative rigorous testing in nonlinear (large amplitude) regime as an extension to standard tests using small-amplitude whistler waves. Quantitative tests of accuracy and performance of the implemented code show the fidelity of the proposed approach.

physics.comp-ph↗