A simple source for a plasma

We have succeeded in producing a plasma which contained about 70% negative ions. This has been achieved by evaporating powder directly into the magnetized potassium plasma column of a Q-machine. The source is a cylindrical stainless steel box with lids that each have a circular hole with an inner diameter equal to that of the plasma column. This source can be heated to about . The obtained density has been inferred from the decrease in the electron saturation current to a heated probe or to a heated collector and values of almost have been obtained.