Experimental and simulation study of helium plasma transport during ion cyclotron resonance heating in MPS-LD

The linear plasma devices (LPDs) can provide a good platform to experimentally simulate the divertor physics. MPS-LD is a new LPD, which uses ion cyclotron resonance heating (ICRH) to raise the ion temperature (Ti). In this work, the helium plasma transport experiments with/without ICRH are carried out, and the corresponding plasma transport modeling is performed by using SOLPS-ITER to study the effects of charge-exchange (CX) collisions and helium atomic density (nHe) on ICRH, to optimize the heating efficiency. The ion energy is diagnosed by self-developed retarding potential analyzer (RPA). Firstly, the SOLPS-ITER simulation without ICRH is benchmarked with the experimental results, showing well agreement. Subsequently, Ti with ICRH is measured by using RPA, and corresponding plasma transport modeling with ICRH is carried out. The experimental and simulation results show that Ti increases almost linearly with ICRH power. When the ICRH power is 10 kW, Ti can reach approximately a dozen eV at the axis, and higher at the outer boundary, but near the target Ti is still around 1 eV. Next, the optimization of ICRH efficiency is further studied by SOLPS-ITER, and the significant effect of enhanced CX collision rate on preventing Ti raising is soundly demonstrated. This reveals the necessity of reducing in the heating region. Finally, the SOLPS-ITER simulation reveals that when differential pumping is applied, the closer the skimmer is to the plasma, the more effectively the in the auxiliary heating region can be reduced. The relationship that affects Ti by influencing the charge-exchange collisions source is confirmed. Moreover, the corresponding relationship between different CX collision rate and is discovered. The present work provides a potential way to optimize ICRH to realize high heating efficiency in future work.