Passive cyclotron current drive for fusion plasmas

The creation of toroidal current using cyclotron radiation in a “passive” way is, together with the well known bootstrap current, an interesting method for stationary current drive in high-temperature fusion reactors. Here, instead of externally applied RF-waves, fish-scale like structures at the first wall help to create enough asymmetry in the self generated cyclotron radiation intensity to drive a current within the plasma. The problem of computing passive cyclotron current drive consists of actually two linked problems, which are the computation of the electron equilibrium under the presence of self-generated radiation, and the computation of the photon equilibrium in a bounded system with a distorted electron distribution. This system of integro-differential equations cannot be solved directly in an efficient way. Therefore a linearization procedure was developed to decouple both sets of equations, finally linked through a generalized local current drive efficiency. The improved formulas for this efficiency take into account the differential and integral part of the relativistic Coulomb collision operator as well as the linearized electromagnetic collision term. The resulting linear equation is solved with the help of Green functions using the expansion over the angular eigenfunctions. The problem of the exact accounting for the wall profile effects was reduced to the solution of a Fredholm-type integral equation of the 2^nd-kind. Based on all this an extensive computer code was developed to compute the passively driven current as well as radiation losses, radiation transport and overall efficiencies. The results there from give an interesting and very detailed insight into the problems related to passive cyclotron current drive