Design features and initial operation of a linear plasma device for the feasibility study of charge separation in curved magnetic field

Mitigation of heat flux impinging on divertor plates is a critical engineering issue even for the fusion reactor adopting innovative super-X divertor. In this work, we are exploring the possibility for resolving this problem by converting a substantial portion of thermal energy of ions into electricity in front of the divertor plates. Since successful energy conversion is followed by the separation of electrons from the plasma, the rigorous investigation for the conditions of efficient charge separation is essential. Considering that the charge separation is affected by intricate relations between plasma density, drift velocity, Larmor radius, and field curvature, we have recently designed and constructed a new linear plasma device at Seoul National University for studying the feasibility of the charge separation by curved magnetic field. The device consists of the driving section including a typical electron cyclotron resonance (ECR) plasma source operating at 2.45 GHz wave frequency and the diffusion section where a cylindrical chamber is surrounded by a pair of solenoid coils for generating various curved magnetic field structures. The plasma density in the experimental region is measured to be around the middle of 1015 m−3 for the optimum ECR field, depending on the gas pressure and microwave power. The preliminary results clearly show that the charged particles in the plasma with a density range of 1015 m−3 can be separated quite well by an extremely slanted cusp magnetic field. We are planning to increase the microwave power to increase the plasma density up to 1017 m−3, making it possible to investigate charge separation at higher density condition.