Collisional effects on trapped electron instabilities

Abstract

The effects of collisions on dissipative trapped electron instabilities are evaluated by distinguishing between the perpendicular and parallel electron velocity components when calculating trapped and untrapped electron contributions. The growth rate is obtained for all regimes of collisionality and reduces to previous results in appropriate limits. It is shown that the dominant effect of finite collisionality is to determine the number of trapped and untrapped electrons and that collisional broadening removes the resonant electron response only for collision frequencies greater than or equal to ten times the wave frequency, νe≳10ω. For such large νe/ω, ion-ion collisions are found to exert a far stronger stabilizing influence than broadening.