Fluctuation-induced dynamo effect in a magnetic confinement plasma
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Mao, W. Z. (ORCID:0000000206768462)↗
Engineering topics
Lian, H.
Publications and source records attributed to Lian, H..
Non-inductive plasma vertical position measurement for the 1056 s discharge on EAST
Vertical position stability plays a crucial role in maintaining safe and reliable plasma operation for long-pulse fusion devices. In general, the vertical position is measured by using inductive magnetic coils installed inside the vacuum vessel; however, the integration drift effects are inherent for steady-state or long-pulse plasma operation. Further, developing a non-magnetic approach provides a fusion reactor-relevant steady-state solution that avoids the negative impact of integration drift. In this paper, we compare the non-inductively determined vertical position achieved by line-integrated interferometer and polarimeter measurements to that employing an inductive flux loop for a 1056 s discharge recently achieved on EAST (Experimental Advanced Superconducting Tokamak). Experimental results show that the non-inductive measurement is more robust than flux loops after 300 s if the integrator is not reset to suppress integrator drift. Real-time vertical position control using the non-inductive system is proposed for the next EAST experimental campaign.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Observation of synergy between lower hybrid waves at two frequencies in EAST
Synergistic effects between two frequencies of lower hybrid (LH) waves—operating at 2.45 and 4.6 GHz—were observed in experiment on EAST for the first time. At low density (ne,lin≈2.0×1019 m−3), simultaneous injection of a 65/35 mix of 2.45/4.6 GHz power achieved an lower hybrid current drive efficiency that was 25% higher than what should be expected from the linear combination of the two sources. The experiment was interpreted with time-dependent simulations, using the equilibrium and transport solver TRANSP, coupled with the ray-tracing code GENRAY and the Fokker–Planck solver CQL3D. For each discharge, profiles of current and hard x-rays from simulation and measurement agree within uncertainties. An examination of the electron distribution function indicates that the LH synergy is supported by the increased width of the LH resonance plateau in the simultaneous injection case compared to independent injection.
Choi, W. (ORCID:0000000268912300)↗
Effect of edge plasma density on hot spot in LHCD plasma in EAST
Hot spots are a serious challenge limiting long pulse operation with lower hybrid current drive (LHCD) in tokamaks. Here, in order to mitigate hot spots in the guard limiter and improve LHCD capability, the effect of edge plasma density on inducing hot spots and current drive has been studied in EAST. The temperature in the guard limiter of the LH antenna, inducing hot spot directly, increases with edge density and LH power. Studies show that the hot spot is mainly ascribed to the heat flux in front of LH antenna. Further simulation indicates that such spots correspond to the peak position of edge density due to local LH electric field. In addition, due to the stronger parametric instability (PI) behavior in the case of higher edge density, the current drive capability decreases with edge density. Strike-point splitting behaviour appears as density increase, in agreement with current profiles in the edge region and the reduction of total driven current, suggesting that more power is deposited in the edge region, which then contributes more to hot spot formation. These studies offer one possible idea to optimize the edge density so as to satisfy the coupling, mitigate the heat flux in the guard limiter, and improve current drive capability in fusion devices.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗