Ion-Probe Current in a Magnetized Plasma

Current-voltage characteristics of Langmuir probes in a strong magnetic field are presented. The experiments were performed using argon or helium gases with pressure 0.1-5.6 mTorr and the plasma density ranging from 1011 to 1012 cm−3 for the field 1-5.5 kG. It is found that (1) for electron collection a cylindrical probe behaves like a disk; (2) the ion retardation part becomes unmasked over positive potentials as a result of decreased electron current; (3) the slope of its logarithmic plot gives the ion temperature; and (4) its values (nearly equal to the electron temperatures of 0.3-1.5 eV) derived from the slope seem to be the true temperatures. Errors and limiting conditions for the determination of ion temperatures are discussed.