1. EX/P1-29. Impact of isotopic effect on density limit and LHCD efficiency in the FT-2 experiments
S.I. Lashkul, A.B. Altukhov, A.D. Gurchenko, E.Z. Gusakov, V.V. Dyachenko, L.A. Esipov, M.A. Irzak, M.Yu. Kantor, D.V. Kouprienko, A.A. Perevalov1, A.N. Saveliev, S.V. Shatalin1, A.Yu. Stepanov
Ioffe Physical-Technical Institute, Politekhnicheskaya 26, St.Petersburg, Russia
R=0.55 m, a=0.08 m, BT ≤ 3T, Ipl=19÷40 kA, ∆tPL=50ms fo = 920МHz, PRF<200kW , ∆tRF from 30ms to 36ms, IRF= (∆Upl / Upl) Ipl.
The LH resonance density: for hydrogen plasma nLН ≈ 3.5 1019 m-3, for deuterium plasma nLH ≈ 1020m-3 .
Fig. 1. The dependence of LHCD efficiency ηCD = IRFN R<ne> (points) on isotopic plasma content (H2 / D2), where IRFN = IRF/ PRF. The minimal value of FCX/(dFCX/dne) (marked by vert. arrows) is an indicator of direct absorption of LHW by plasma ions. Where FCX(1575eV) - fast charge-exchange neutral flux.
Fig Frequency spectrum of the RF probe measured in an LHCD deuterium plasma. <ne> = 3 1019m-3 (green/blue lines) and <ne> = 4.2 1019m-3 (black line). Positions of the deuterium (hydrogen) satellites are indicated by arrows.
Fig. 3. Dynamics of the plasma density ne (r) and temperature Te(r) radial profiles measured by thomson scattering in the deuterium plasma LHCD experiment.
In the hot hydrogen plasma (Ipl = 32kA) there is no appreciable density gap between the LHCD suppression (nDL) and the appearance of fast neutrals. In the hot deuterium plasma there is the density gap due to nLH(D2)>>nLH(H2). The role of parametric instabilities in the LHCD switch-off has to be considered when density limit nDL<nLH is observed.
In deuterium plasma according to FRTC and ASTRA codes modeling the density and central Te rise during LHCD happens due to strong reduction in the electron transport in the r<3cm region where the magnetic shear s vanishes, and the value of thermal diffusivity χe, eff decreases. In hydrogen plasma this effect is weak.