PASSIVE CYCLOTRON CURRENT DRIVE EFFICIENCY FOR RELATIVISTIC TOROIDAL PLASMAS

In this paper we present results of analytical and numerical studies o f the passive cyclotron current drive efficiency in mildly relativisti c toroidal plasmas. The problem of linearization and separation of the electron and photon balance equations becomes nontrivial for high-tem perature plasmas (e.g., D-He-3) with low electron pressure (beta(e)<0. 1) due to the increased effect of radiation friction. The conditions u nder which this separation is possible is derived in this paper. The l inearized problem for the electron distribution is formulated in the f orm of a standard variational principle, which includes both Coulomb c ollisions and ''collisions'' due to cyclotron radiation. The reduced v ariational principle for the current drive efficiency (generalized Spi tzer-Harm function) is derived, as well as its bounce-averaged form fo r toroidal plasmas. Finally, a convenient form of the passive cyclotro n current drive efficiency is introduced, which can be used for a self -consistent modeling of passive cyclotron current generation in tokama ks with the help of fish-scale structures [see the companion paper, W. Kernbichler and S. Kasilov, Phys. Plasmas 3, 4128 (1996)]. (C) 1996 A merican Institute of Physics.