Detached plasma control by negative ion in divertor simulator

We have developed a new way to stably maintain a detached plasma based on feedback control of the negative hydrogen ion (H−) density in the linear divertor plasma simulator, TPD-SheetIV. Measurements of the negative hydrogen ion density, nH−, the heat load to the target plate, Q, and the secondary gas-flow rate, GDiv, were carried out as a function of neutral pressure in the plasma. A small amount of secondary gas puffing strongly reduced Q and rapidly increased nH− in the periphery of the plasma without increased radiative and three-body recombination. The detached plasma is steadily maintained in the region of the target plate by rapidly varying GDiv so as to maximize the value of nH− and keep PDiv constant. The new system has achieved the goal of reducing both Q and amount of GDiv in a detached plasma.