1 - Nuclear Sciences and Applications - IAEA

R 6
IAEA-CN-50/E-IM
0.5 10 1.5
Ne(rr40cm) fio'cn
FIG. 1. Specific loading resistance versus edge density at r = 40 cm (a = 46 cm). The lines are the
computed results. The right ordinate gives the required antenna voltage VA to launch 1 MW.
2. ANTENNA PROPERTIES
The 3 MW of installed power are delivered to two antenna pairs, each one
radially movable with respect to the plasma [4, 5], The antenna pairs are situated in
diametrically opposite toroidal positions and are fed in phase (0) or out of phase (IT).
•K phasing voids the antenna spectrum of less damped low toroidal wavenumbers
kz [5]. The practical problem encountered in most experiments with ir phasing [6] is
a sometimes strongly reduced loading with respect to the in-phase operation,
resulting in more stringent voltage requirements. Figure 1 demonstrates that this
need not always be the case: our experimental loading results for the ir phasing are
even somewhat higher than for the 0 phasing. The voltage VA to be applied to a pair
in order to launch 1 MW remains reasonably low, as can be seen on the right
ordinate of Fig. 1. One also notes the good agreement with the specific resistance
predicted by our coupling codes [5]. The beneficial effects of ir phasing to be
reported in Section 4 are thus obtained without extra electrical solicitation of the
ICRH system. The reasons for this are extensively discussed in Ref. [5].
3. ELEMENTS FROM WAVE PHYSICS
Changing from HFS to LFS launch is expected to switch the dominant heating
scenario from mode conversion (MC) to minority heating (MH) and to strongly
modify the wave absorptivity, as confirmed by detailed studies using a 1-D full wave
code [7]. Figure 2(a) shows, for a typical plasma condition, the damping capability,
defined as the fraction Ps of the launched power that is absorbed after the wave has
made two transits over the plasma cross-section (e.g. from LFS to HFS back to LFS),
for the old HFS scheme and the 0 and the ir LFS mode. The calculations are
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