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

Abstract

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 ( T _i ). 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 ( n _He ) 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, T _i with ICRH is measured by using RPA, and corresponding plasma transport modeling with ICRH is carried out. The experimental and simulation results show that T _i increases almost linearly with ICRH power. When the ICRH power is 10 kW, T _i can reach approximately a dozen eV at the axis, and higher at the outer boundary, but near the target T _i 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 T _i raising is soundly demonstrated. This reveals the necessity of reducing ${n_{{\text{He}}}}$ 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 ${{{n}}_{\text{He}}}$ in the auxiliary heating region can be reduced. The relationship that ${n_{{\text{He}}}}$ affects T _i by influencing the charge-exchange collisions source is confirmed. Moreover, the corresponding relationship between different CX collision rate and ${n_{{\text{He}}}}$ is discovered. The present work provides a potential way to optimize ICRH to realize high heating efficiency in future work.

Keywords

• plasma transport
• ICRH
• SOLPS-ITER
• charge-exchange collision
• differential pumping