Evolution of photoionization two-stream instability in collisional plasma

Abstract A kinetic model which takes into account gas jet photoionization by an ultrashort linearly polarized EUV/X-ray free electron laser (FEL) pulse, a self-generated low frequency electric field, and elastic electron scattering on atoms is introduced to study the photoionization two-stream (PITS) instability. The evolution of PITS instability is described in terms of an integral equation for electron density perturbations. This paper presents a generalization of previous theories of the PITS instability in collisionless plasmas. The instability is produced by the anisotropy of photoionized electrons and is strongly affected by electron–atom collisions. Relaxation of the PITS instability is studied for different relations between the FEL pulse duration, the instability growth time, and the electron collision time.