Confinement and transport in EC heated RI-mode discharges in TEXTOR

Abstract

This paper reports on experiments in TEXTOR with electron cyclotron resonance heating (ECRH) of radiatively improved (RI) mode discharges. With ECRH the energy content of RI-mode discharges can be increased without the normally observed power degradation in confinement time. The experiments are described and the effects of ECRH on global confinement and local plasma parameters of RI-mode discharges are discussed; the favourable scaling of energy content is due to a zone of low electron thermal transport just outside the sawtooth inversion radius. Moreover, the heating effect of ECRH in the RI-mode is compared with the effect in L-mode; this comparison sheds some light on the physics of electron thermal transport in RI-mode discharges.

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

“…In TEXTOR, O2 heating was applied at densities above the X2 cutoff [9]. The inferred absorption of up to 60% under these conditions was in rough agreement with the calculated value.…”

Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field

“…,N) is a sequence of times in the mapping (9), and the averaging is done over a large number of mapping iterations N , N 1. The profile of ω eff (J ) is flattened in the region J mn − J mn /2 < J < J mn + J mn /2 near the resonant tori J mn , where J mn is the resonance width (20). This is shown by curve 5 in Fig.…”

“…7 in the whole region 0 < J < 1 for the large Kubo number K = 100 (a) and in the region 0.5 < J < 0.55 located near the rational tori ω = 1/3 for the several values of K = 1,2,5, and 100 (b). The values for the other parameters are chosen: q 0 = 0.8, q a = 5, γ ≡ 1, 20 n 50, and α = 5/6, which corresponds to the power spectrum |H mn | 2 ∼ n −5/3 , and the 1 The existence of gaps in the density of rational tori has been pointed out already in many above-mentioned works [15][16][17][18][19][20][21][22][23][24][25], however, no quantitative estimations have been presented. Moreover, I could not find the results obtained here in existing literature, although one could expect that this problem has been treated already in number theory or in other fields of physics.…”

“…At present several possible mechanisms, like an ExB flow shear, a zonal flow, or a magnetic shear, have been proposed. One of these issues is the role of low-order magnetic surfaces in the formation transport barriers which have been discussed in a number of works [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Electron Cyclotron Resonance Heating on TEXTOR

“…Although the pulse length of 200 ms is rather limited compared to typical confinement times of ;50 ms in the RI-mode, and the power of only 270 kW is rather small compared to the total heating power of ;2.7 MW in typical RI-mode discharges, first experiments reveal central ECRH in RI-mode plasmas to be remarkably effective 16 : the total stored energy rises in proportion to the full power of central ECRH~see Fig. 4!, instead of an efficacy of only 30% as could be expected on the basis of the RI-mode scaling.…”