Abstract
The effects of resonant magnetic perturbation (RMP) field on impurity radiation, divertor footprint distribution, and core plasma transport are investigated in the detachment discharges of the Large Helical Device (LHD). The RMP with m/n = 1/1 mode creates an edge magnetic island in the stochastic layer, which enhances the impurity emission from low charge states, C2+ and C3+, and then triggers a detachment transition. Emission from the higher charge states, C4+ and C5+, implies enhanced penetration of impurities during the detachment phase with RMP. The toroidal divertor particle flux distribution exhibits n = 1 mode structure in both the attached and detached phases, but with a large toroidal phase shift between the two phases. The distribution in the attached phase is well correlated with the magnetic footprint of field line connection length calculated by the vacuum approximation. During the detached phase, however, the phase shift is not well explained by the vacuum approximation, where a significant plasma response to the external RMP is observed. The energy confinement time becomes systematically shorter with RMP application due to the shrinkage of plasma volume caused by the edge magnetic island. On the other hand, the pressure profile during detachment with RMP is found to be more peaked than without RMP. The analysis using the core transport code TASK3D, considering the heating profiles of neutral beam injection, shows no significant transport degradation during detachment with RMP application, even with the enhanced radiation, reduced divertor flux, and possible impurity penetration.
Highlights
We investigate the 3D structure of the divertor detachment distribution, which is found to be not uniform in toroidal direction with resonant magnetic perturbation (RMP) application, which is correlated with connection length distribution at the divertor plates to a certain extent
The results show that the particle transport is well correlated with the LC distribution, to a certain extent, obtained by the vacuum approximation, and can be controlled by the RMP application in the attached phase
The effects of RMP application on the detachment operation in LHD have been investigated in terms of impurity radiation, toroidal distribution of detachment, and the core plasma transport
Summary
In order to place the resonant layer at the edge stochastic layer, we select a magnetic configuration with a magnetic axis (Rax) at R = 3.9 m and Bt = 2.54 T (clockwise direction in the top view of torus). In this configuration, the m/n=1/1 magnetic island is created in the edge stochastic layer, as shown in the lower half of Fig. (b). When they come close to the helical coils, the island width becomes narrow due to the increased B field strength
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