Pulsed high power free-electron-lasers (FELs) offer new possibilities for the current drive in tokamaks. High intensity FELs apply to the excitation of nonlinear wave-wave processes, such as beat-waves (BW) and stimulated Raman scattering (SRS), in which large phase velocity (vph>>ve) electrostatic modes are generated. These can accelerate resonant electrons to high parallel velocities v||∼vph, which produces a slowly decaying current. Furthermore, the fast electrons with v||>>v are not toroidally trapped into banana orbits. The operation at high frequencies provides for the FEL beam an easy access into the plasma centre. This makes possible to suppress sawtooth activity by profile control and to expand the operational limits in parameter space. Raman and beat-wave methods apply particularly well to bootstrap current seeding, which may considerably enhance the overall current drive efficiency. Both Raman forward (SRS-F) and backward (SRS-B) scattering can be applied to current drive. At high, reactor relevant temperatures SRS-F is the dominant process, because SRS-B is suppressed due to heavy damping of the plasma wave. At temperatures of a few keV, SRS-B dominates because of its short gain length. In this report we shall estimate the current drive efficiency at temperatures relevant for MTX and for a tokamak reactor. We shall also consider the dependence of the efficiency on the peak intensity of FEL in these two cases.
|Series||Europhysics Conference Abstracts|
|Conference||18th European Conference on Controlled Fusion Plasma and Plasma Physics|
|Period||3/06/91 → 7/06/91|