Microstability properties of the sheath region of a field-reversed configuration

Abstract

An analysis of the microstability properties of the sheath region of a field‐reversed configuration is performed. Attention is focused on the lower‐hybrid‐drift instability, a mode known to be important in devices with similar parametric conditions. This mode is thought to play a significant role in determining the confinement properties of a field‐reversed configuration. Specifically, a model profile characteristic of the sheath region is constructed and analyzed in detail, both theoretically, by means of a nonlocal kinetic theory, and computationally, by means of a hybrid simulation technique. The lower‐hybrid‐drift is found to be unstable under typical sheath conditions. The theoretically predicted growth rate and the variation of the growth rate with wavenumber is found to be in good agreement with the growth characteristics deduced from the simulation. By means of the hybrid simulation technique, the lower‐hybrid‐drift has been simulated at drift velocities as low as 0.2v_i with m_i/m_e =100 and 0.3v_i with m_i/m_e =3672.