Magnetic field effects on instabilities driven by a field-aligned relativistic warm electron beam and warm bulk electrons

• Instabilities driven by relativistic electron beams are being investigated due to their importance for plasma heating and electromagnetic field generation in astrophysical and laboratory plasmas. Particle-in-cell (PIC) simulations of initially unmagnetized colliding plasmas have demonstrated the generation of strong magnetic fields and a moderate electron acceleration. The inclusion of a flow-aligned magnetic field suppresses the electromagnetic filamentation instability and PIC simulations have shown that the plasma dynamics turns quasi-electrostatic. To quantify the impact of the magnetic field, we have analyzed numerically a magnetized multi-fluid model that includes a kinetic pressure term. This fluid model allows us to examine the beam-driven instability at all angles between the wavevector and the magnetic field vector. More accurate kinetic models typically focus only on the filamentation instability, due to the increased analytical complexity. We present here the fluid model and a growth rate map of the entire k-space for a beam Lorentz factor 4. We verify that the two-stream, mixed mode and filamentation instability belong to the same wave branch and that the magnetic field selects the fastest-growing mode. We estimate the magnetic fields required to suppress the filamentation and the mixed mode instabilities.

Keyword

plasma physics

TECHNOLOGY

TEKNIKVETENSKAP

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