Investigation of impurity confinement in lower hybrid wave heated plasma on EAST tokamak

Abstract

The transient perturbation method with metallic impurities such as iron (Fe, Z = 26) and copper (Cu, Z = 29) induced in plasma-material interaction (PMI) procedure is used to investigate the impurity confinement characters in lower hybrid wave (LHW) heated EAST sawtooth-free plasma. The dependence of metallic impurities confinement time on plasma parameters (e.g. plasma current, toroidal magnetic field, electron density and heating power) are investigated in ohmic and LHW heated plasma. It is shown that LHW heating plays an important role in the reduction of the impurity confinement time in L-mode discharges on EAST. The impurity confinement time scaling is given as 42I 0.32 P B 0.2 t n 0.43 e P −0.4 total on EAST, which is close to the observed scaling on Tore Supra and JET. Furthermore, the LHW heated high-enhanced-recycling (HER) H-mode discharges with ~25 kHz edge coherent modes (ECM), which have lower impurity confinement time and higher energy confinement time, provide promising candidates for high performance and steady state operation on EAST.

Metallic impurity content behavior during ICRH-heated L-mode discharges in EAST

“…One may find detailed information of the spectrometer in Ref. [18,19]. Lines intensity are systematically normalized by lineaveraged electron density to indicate impurity content.…”

“…In the present regime of operation, since relatively little power is injected, ICRF absorption efficiency is often poor compared to those of lower hybrid. In addition, larger power fraction is radiated during ICRH than during LH (generally above 70% [19]). As a conclusion, (i) the divertor target is mostly sensitive to the conducted power, and (ii) the power conducted by LH is often much higher than the one conducted by ICRH, therefore (iii) divertor region is well-correlated to total injected power (mostly LH) rather than ICRH.…”

Reduction of impurity confinement time by combined heating of LHW and ECRH in EAST*

“…This spontaneous TPM has been successfully used to study the confinement properties of Fe and Cu in LHW-heated sawtooth-free plasma on EAST. [13] Such a spontaneous TPM of metallic impurities always occurs when the distance of outer gap between the limiter and the last closed flux surface (D gapout ) is relatively small. It is found that more than 80% of transient perturbation events happen when D gapout < 4 cm, such as in the ohmic plasma shown in Fig.…”

“…[4][5][6][7] Widely used in DIII-D, [8,9] ASDEX-U, [10] TCV, [11] etc., the on-axis ECRH can provide a more peaked electron temperature in plasma core so as to avoid the impurity accumulation. The LHW heating utilized on Tore Supra [12] and EAST [13,14] also shows an apparent reduction of core impurity confinement, due to the fact that LHW can heat central electron and generate turbulent transport. The study of the core impurity confinement properties in LHW and ECRH heated plasmas was inspired by the intense central electron heating.…”

Fusion Research and International Collaboration in the Asian Region

“…A simulation code analysis strongly suggests that an impurity transport barrier is formed in the hollow n e profile based on a neoclassical effect on the ion density gradient. In EAST, it is found that the confinement of metallic impurities can be reduced by LHW heating [40].…”