Rigid Rotor Model for Field-Reversed Configurations, Revisited

Abstract

It is shown that the ratio between ion and electron macroscopic rotational frequencies in rigid rotor profiles, Ω_l⁄Ω_e, is not a free parameter when global charge neutrality is taken into account. For most applications of interest Ω_l⁄Ω_e≤−T_l⁄T_e and depends on global characteristics of the confined plasma, as number of confined particles per unit length, T_l⁄T_e and the diamagnetism. Global charge neutrality is justified on the facts that in weakly coupled plasmas, the electrostatic energy of each species should be much lower than the respective thermal energy on average, and that no experimental evidence of any net charge of the plasma in theta-pinches or field-reversed configurations is reported. Connections of the present results with previous stability studies based on the rigid rotor model are discussed and some comparison with experimental results, supporting the hypothesis of global charge neutrality, are presented.