Experimental investigations of LHW–plasma coupling and current drive related to achieving H-mode plasmas in EAST

Abstract

Aimed at high-confinement (H-mode) plasmas in the Experimental Advanced Superconducting Tokamak (EAST), the effect of local gas puffing from electron and ion sides of a lower hybrid wave (LHW) antenna on LHW–plasma coupling and high-density experiments with lower hybrid current drive (LHCD) are investigated in EAST. Experimental results show that gas puffing from the electron side is more favourable to improve coupling compared with gas puffing from the ion side. Investigations indicate that LHW–plasma coupling without gas puffing is affected by the density near the LHW grill (grill density), hence leading to multi-transition of low–high–low (L–H–L) confinement, with a correspondingly periodic characteristic behaviour in the plasma radiation. High-density experiments with LHCD suggest that strong lithiation gives a significant improvement on current drive efficiency in the higher density region than 2 × 1019 m−3. Studies indicate that the sharp decrease in current drive efficiency is mainly correlated with parametric decay instability. Using lithium coating and gas puffing from the electron side of the LHW antenna, an H-mode plasma is obtained by LHCD in a wide range of parameters, whether LHW is deposited inside the half-minor radius or not, implying that a central and large driven current is not a necessary condition for the H-mode plasma. H-mode is investigated with CRONOS.

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

“…LHCD experiments on many tokamaks (Pericoli-Ridolfini, Giannone & Bartiromo 1994;Cesario et al 2010;Wallace et al 2010;Cesario et al 2011) have shown a decrease in non-thermal tails and a drop in bremsstrahlung emission much steeper than 1/n e at high densities, which is stronger than expected based on current models. Similar results (Ding et al 2013a have also been reported in EAST. Some possible mechanisms, including collisional absorption (CA) (Bonoli & Englade 1986), parametric instabilities (PI) (Liu & (Bonoli & Ott 1982;Peysson et al 2011), individually or simultaneously, have been identified to preclude the penetration of LHWs, dissipating the power in the plasma periphery and degrading LH efficiency.…”

Self-consistent quasi-linear modelling of Lower Hybrid Current Drive in ITER and DEMO

“…The semi-analytical considerations have also been supported by full 2D numerical approach (not reported here but in Ref. [8] be tested in an experiment using a small Δk || (≈0.05) but relatively large n ||0 (≈2.8) to compensate the lower electron temperatures of the today's tokamaks, e.g., EAST [18], ranging at around 5 keV in the core. Furthermore, a small value of Δk || should be achieved in reactor devices since the large toroidal dimensions allows to a have a grill with a large number of elementary waveguides.…”

Quasi-linear modeling of lower hybrid current drive in ITER and DEMO

“…The full 2D numerical results, obtained by the ray star code, are supported by analytical considerations. The above results could be tested in an experiment using a small Δn || (≈0.083) but relatively large n ||0 (≈2.8) to compensate the lower electron temperatures of the today's tokamaks, e.g., EAST [24], ranging at around 5 keV in the core. Furthermore, a small value of Δn || should be achieved in reactor devices since the large toroidal dimensions allows to a have a grill with a large number of elementary waveguides.…”