Photoemission driven electron two-stream instability (ETSI) and evolution of plasma sheath

Analysis related to the onset and evolution of the electron two stream instability (ETSI) near a surface with a continuous photoemission flux is presented. With the help of a particle in cell simulation code, it is shown that when a surface emits photoelectrons due to exposure to ultraviolet photons (or due to similar mechanisms), it may lead to the onset of the ETSI due to the relative bulk velocity difference between the photoelectrons and the plasma electrons. It is shown that the ETSI thus developed is sustained through the lifetime of the plasma and prevents thermalization of the electrons, which leads to a distortion in the electron velocity distribution function (EVDF) resulting a high energy tail, at least near the surface. We have shown that the resultant EVDF can be highly Lorentzian with a spectral index of similar to 1.5. The simulation results are supported with the corresponding theory, which are found to be in good agreement. Published under license by AIP Publishing.