Experimental evaluation of space charge limited emission current from tungsten surface in high density helium plasma

A space charge effect on thermoelectron emission current from a tungsten plate has been experimentally investigated in a high density helium plasma. Experimental result shows that the space charge limited current from the tungsten target plate, which is heated by the plasma irradiation, tends to be saturated with an increase in a sheath voltage, which can be predicted by the developed new formula based on the boundary condition of zero electric field on the material surface.