Divertor Simulation Studies by generating High Heat Flux Plasmas

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Objectives of this research are as follows : l. Construction of fast scanning probe system for plasma diagnostics ; 2. Proof of principle of generation of high heat flux plasmas ; 3. Experimental and theoretical analysis of sheath characteristics formed at the interface between divertor plasma and plasma facing materials.1. Fast scanning probe is successfully constructed for high heat flux plasma diagnostics. The scanning length is 20cm, its time for go and return is 0.8sec, and the starting position can be changed by 15cm in horizontal direction and by 10cm in vertical one. The probe characteristics can be taken every 2mm. This system was found to be applicable for plasmas whose density is up to 6xlO^<19>m^<-3>.2. Indirectly heated large LaB, , disc cathode is successfully established for high, heat flux plasma generator. Up to 100A steady state discharge, current has been obtained by using the above cathode assembly, in which the plasma density reaches 5xlO^<18>m^<-3> and the electronic temperature is about lOeV with the diameter of as much as 12cm.3. Sheath theory for two electric temperature plasma was established. The plasma with two component of electrons is generated in a high repetition tokamak using a themoelectron emitter. The experiments show that the suppression of sheath voltage is observed for the materials having high secondary electron emission coefficient, like gold, and that the surface conditions are important for carbon, W, and Mo.