Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

Abstract

Using a 2 MW 2.45 GHz lower hybrid wave (LHW) system installed in experimental advanced superconducting tokamak, we have systematically carried out LHW-plasma coupling and lower hybrid current drive experiments in both divertor (double null and lower single null) and limiter plasma configuration with plasma current (I p ) $ 250 kA and central line averaged density (n e ) $ 1.0-1.3 Â 10 19 m À3 recently. Results show that the reflection coefficient (RC) first is flat up to some distance between plasma and LHW grill, and then increases with the distance. Studies indicate that with the same plasma parameters, the best coupling is obtained in the limiter case (with plasma leaning on the inner wall), followed by the lower single null, and the one with the worst coupling is the double null configuration, explained by different magnetic connection length. The RCs in the different poloidal rows show that they have different coupling characteristics, possibly due to local magnetic connection length. Current drive efficiency has been investigated by a least squares fit with N peak == ¼ 2:1, where N peak == is the peak value of parallel refractive index of the launched wave. Results show that there is no obvious difference in the current drive efficiency between double null and lower single null cases, whereas the efficiency is somewhat small in the limiter configuration. This is in agreement with the ray tracing=Fokker-Planck code simulation by LUKE=C3PO and can be interpreted by the power spectrum up-shift factor in different plasma configurations. A transformer recharge is realized with $0.8 MW LHW power and the energy conversion efficiency from LHW to poloidal field energy is about 2%.

Observation of pedestal turbulence in edge localized mode-free H-mode on experimental advanced superconducting tokamak

“…28 The H-mode discharges were achieved by LHW, 29 ICRF, 30 or their combination. The energy confinement of these RF heated H-modes has been studied.…”

Effect of magnetic islands on lower hybrid current drive in experimental advanced superconductor tokamak plasma with circular cross section

“…For the present LHW system on EAST of 2 MW/2.45 GHz, it consists of 20 main multijunction waveguides arranged in an array of five rows and four columns. 9 The n k spectrum radiated from the launcher is usually centered at 2.1 but can be varied between 1.85 and 2.58 by varying the phase difference between adjacent main waveguides from À90 to 180 . Thus, we perform the calculation with many rays and each ray has a definite initial n k and launched power that according to Brambilla's treatment with n peak k ¼ 2:1, as shown in Fig.…”

“…6 On Experimental Advanced Superconductor Tokamak (EAST), LHCD has been used to achieve a long-pulse Hmode discharge to provide an intrinsic boundary control for edge localized modes. 8,9 If the accessibility condition is satisfied, the coupled lower hybrid wave from an external antenna can propagate into core region with high plasma density and temperature. As the wave phase velocity becomes comparable with the electron thermal velocity, the LHW can interact with electrons at high velocities around three times the electron thermal velocity via Landau damping.…”

Studies of challenge in lower hybrid current drive capability at high density regime in experimental advanced superconducting tokamak

“…To improve LHW-plasma coupling, local gas puffing near the antenna has been developed, which has been studied in JT-60U, ASDEX, JET, Tore-supra, HT-7 Ikeda et al 1994;Pericoli-Ridolfini et al 2004;Ekedahl et al 2005Ekedahl et al , 2009Ekedahl et al , 2012Ding et al 2010). Also, in EAST, with the 2.45 GHz LHCD system, local gas puffing from the electron drift side (GIM_e) and ion drift side Studies of challenge in LHCD capability at high density regime in EAST 3 FIGURE 2.…”

“…In order to obtain the scientific goal of EAST (a long pulse and high performance), two LHCD systems have been developed and exploited on EAST, operating, respectively, at 2.45 GHz (4 MW) (Ding et al 2011 and 4.6 GHz (6 MW) (Ding et al 2013a,b). Typical spectra calculated by an advanced lower hybrid antenna (ALOHA) (Hillairet et al 2010) are shown in figure 1, in which N // is the refractive index in the parallel direction, N peak // is the corresponding peak value and Φ refers to the phase difference between the adjacent main waveguides.…”