ASPECT-RATIO DEPENDENCE OF ALFVEN-WAVE CURRENT DRIVE AND ITS EFFICIENCY IN SIMULATED TOKAMAK PLASMAS - A SYSTEMATIC, FULL-WAVE EQUATION INVESTIGATION

We investigate theoretically the aspect-ratio dependence of Alfven-wav e current drive (AWCD) in 'simulated' tokamaks, in the range 1.1 less than or equal to R/a less than or equal to 10 (where R and a are the m ajor and minor radii, respectively). The study is carried out within t he framework of resistive MHD, and is based on the consistent solution of the full-wave equation (E-parallel to not equal 0); both shear and simulated toroidicity effects are taken into account. The AWCD includ es components due to (wave) momentum transfer, helicity injection and plasma flow. The aspect-ratio-dependent features investigated include the radial profiles as well as the integrated power absorption, curren t drive and efficiency; the effects of antenna parameters (wavenumbers and frequency) are also explored. The numerical code developed and us ed for these computations has been benchmarked with the aid of analyti cal solutions obtained for the antenna-metallic-wall system in vacuum, as well as by the smooth transition from the vacuum case to the, actu al plasma case. Results of extensive calculations for the so-called Al fven-continuum frequency range are presented and discussed.