Plasma heating by electron cyclotron wave and the temperature effects on lower hybrid current drive on EAST

Abstract

This paper presents the progress in the long - pulse operation of the electron cyclotron (EC) system and the achievements in high - electron temperature plasmas by the combined EC and lower hybrid (LH) waves heating since the EC system was built in 2015. An electron temperature of up to 12 keV with a duration over 100 s was realized by the simultaneous heating of EC and LH waves at the line-averaged density n ̅_e ~ 1.8 *10^19/m^3. The plasma heating effect strongly depends on the location of EC power deposition. H-mode plasmas with solely EC wave auxiliary heating have been obtained on EAST for the first time. These H-mode discharges show an enhanced confinement factor H98(y,2) around 1.0, which is higher than the previous H-mode using LH power alone [G.S. Xu et al Nucl. Fusion 51 (2011) 072001]. The total heating power is very close to the threshold value for L-H transition according to the international tokamak scaling. In addition to the temperature effects inside the separatrix, higher electron temperature produced by EC wave is found to reduce the LH power loss in the scrape-off layer (SOL) due to collisional absorption, which is beneficial to further increase the lower hybrid current drive (LHCD) efficiency. Ray-tracing/Fokker-Planck modeling results indicate that higher electron temperature can shorten the LH wave propagation on EAST in a multiple-pass regime, thus decreasing the collisional dissipation.

Design and analysis of a PAM launcher at 4.6 GHz for a new LHCD system on EAST

“…It is seen that the nominal N || of 2.04 can satisfy the wave accessibility through the pedestal region for the case of moderate line-averaged density (n e ∼ 3.6 × 10 19 m −3 ) with normal B t = 2.5 T, while for the case of high density (n e ∼ 4.7 × 10 19 m −3 ), a higher B t of 2.8 T is required. It is worth pointing out that with this value B t = 2.8 T, the ECRH (with frequency of 140 GHz) power, another important electron heating source on EAST [34], cannot be deposited on axis. In tokamak magnetic configurations, the N || will evolve along the ray paths due to the toroidal effects [35].…”

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

“…Although a pulse length of 10 s is enough for thermal equilibrium, the coupled power in long-pulse operation (>100 s) will be decreased by ∼30% in general, according to the experience on EAST. For example, the maximum coupled power was ∼3.3 MW for 4.6 GHz LHCD system with 10 s-scale pulse length; but for 100 s long-pulse operations, the power level coupled to plasma is limited by ⩽2.3 MW [30]. This is mainly due to the overcurrent fault in the klystron operation.…”