JET-P(91)41

Fast-Wave Current-Drive Efficiency Calculations for JET A2-Antennas

Fast-wave transit-time magnetic-pumping (TTMP) current drive efficiency calculations using ray tracing techniques are presented using A2-antennas for the experiments to be carried out in the divertor phase of the extended JET programme. The antenna plasma coupling problem is properly solved using a full wave solution which allows to incorporate the antenna array directivity and full asymmetric spectrum in the calculations. Current drive calculation at each step of the ray allows to take into account the power deposition profile and the electron trapping effects correctly. The poloidal field effects which change k|| and therefore have important consequences on the current drive efficiencies are also taken into account. It is shown that current drive efficiency factory g @ 0.11 in units of 1020 W/A/m2 is obtained for an electron temperature of 10keV. Synergistic effects between the ICRH and the lower hybrid current drive system in which a population of fast electrons (@100­200keV) is produced is also evaluated. It is found that a 0.5% concentration of 200keV fast electrons would increase the current drive efficiency by 35% at a toroidal mode number n = 11 and this increase could be as large as a factor of 2 at lower n = 2-4.
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JETP91041 1.07 Mb