A new ion pitch-angle diagnostic for magnetized plasmas

An ion pitch-angle diagnostic (PAD) capable of directly measuring the ratio T(I perpendicular to)/E(z) in a magnetized plasma is described. It consists of an ion collector, a plane stainless steel electrode with its axis parallel to magnetic lines of force, which can be slid along the inside of a stainless steel cylindrical tube of inner radius R. The ion collector is insulated from the tube and is biased to a negative potential to collect ions. Calculations show that the ratio III(0) of the collected ion current, when the collector is withdrawn a distance z from the tube entrance, ion the ion current collected at z = 0, depends solely on the ratio of T(I perpendicular to)/E(z). The change of //I(0) with z is found to be insensitive to the absolute magnitude of T(I perpendicular to) and E(z), and to the mass of the ion species. PAD results are presented for N(2) and CF(4) plasmas. Results for N(2) plasmas are shown to compare well with LIF (laser-induced fluorescence) results demonstrating the validity of this diagnostic.