1 - Nuclear Sciences and Applications - IAEA

IAEA-CN-50/E-IV-ll 769
FIG. ]. Real and imaginary parts of NlX versus x for o)c(0)/o> = 0.625, ui 2 p{0)lu>l(0) = 0.6,
c/v,(0) = 16, c/vs(0) = 8, u = 0, dj = 70° and several values of-q.
First we shall analyse the wave propagation and spatial damping in the case
where the SECH resonance takes place in the outer half (low field side) of the plasma
column. At such moderate frequency downshifts, the X-mode is still efficiently
damped in spite of the reduced electron density and temperature values. This observation
can be verified in Fig. 1, where we show the variation of the real and imaginary
parts of the perpendicular wave refractive index of the X-mode with the dimensionless
space co-ordinate x for wc(0)/w = 0.625, a) 2 (0)/«c 2 (0) = 0.6, c/v,(O) = 16,
corresponding to a peak electron temperature T(0) = 1 keV, c/vs(0) = 8, u = 0,
0, = 70° and several values of the fraction of electrons in the non-drifting superthermal
tail, T). Note that the SECH resonance, w = 2«c, takes place at x = 0.75.
In the absence of the superthermal tail the wave damping is strong. For 17 = 0, complete
first pass absorption of the X-mode is achieved at koa = 2 x 10 3 (ko is the
vacuum wavenumber). We see that the presence of the tail enhances the wave absorption
at downshifted frequencies. As the fraction of electrons in the tail increases, the
absorption profile enlarges and the non-thermal contribution to the absorption grows.
This effect is very pronounced at higher electron temperatures. In Fig. 2 we show
Re NlX and Im N±x versus x for c/vt(0) = 8 and c/vs(O) = 4. The other
parameters are the same as in Fig. 1. The results presented indicate that at moderate
bulk electron temperature (T = 1-4 keV) good power deposition profiles
(P(a/2) > 0.5) can be obtained in small and medium size plasmas (koa ;£ 10 3 ). In