Electron injection into diffusive shock acceleration · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Electron injection into diffusive shock acceleration
Plain
Shocks accelerate particles that bounce back and forth across them many times, but electrons are too small to do this until they are already energetic. How a fraction of thermal electrons is pre-energized is the electron injection problem.
Precise · changed · core
Revision 1: Diffusive shock acceleration (DSA, repeated shock crossings by particles scattered by magnetic turbulence) requires electron gyroradii larger than the shock width (of order the ion inertial length). Determine the injection efficiency and the electron-to-proton ratio $K_{\mathrm{ep}}$ at equal energy as functions of Alfvenic Mach number $M_A$, sonic Mach number and shock obliquity $\theta_{Bn}$ at realistic $m_i/m_e$. An answer is $K_{\mathrm{ep}}(M_A, \theta_{Bn})$ from converged kinetic simulations, compared with $K_{\mathrm{ep}} \sim 1e-3\ \text{to}\ 1e-2$ inferred in supernova remnants.
Revision 2: Diffusive shock acceleration (DSA, repeated shock crossings by particles scattered by magnetic turbulence) requires electron gyroradii larger than the shock width (of order the ion inertial length). Determine the injection efficiency and the electron-to-proton ratio $K_{\mathrm{ep}}$ at equal energy as functions of Alfvenic Mach number $M_A$, sonic Mach number and shock obliquity $\theta_{Bn}$ at realistic $m_i/m_e$. An answer is $K_{\mathrm{ep}}(M_A, \theta_{Bn})$ from converged kinetic simulations, compared with $K_{\mathrm{ep}} \sim 10^{-3}\ \text{to}\ 10^{-2}$ inferred in supernova remnants.
Settled by
Long-duration particle-in-cell simulations at realistic mass ratio, confirmed by in-situ spacecraft data at heliospheric shocks.
Kind
well-posed
Answer type
value
References
(empty)
Literature status
partially-resolved
Status note
2025 kinetic simulations proposed a shock-speed-dependent injection threshold for electrons (arXiv:2506.09134).
Posed since
(empty)

Decisions