APPEARANCE OF RADIAL ELECTRIC-FIELD IN SOURCE PLASMA DUE TO EXTRACTION

The interrelation between the source plasma and the beam extraction is described. The extraction of ions is a charge separation process at the extraction boundary and electrons are reflected back into the source plasma. The resulting excess electrons change the potential distribution in the source plasma, which in turn affects such characteristics in the beam extraction as the beam divergence and the total output of the beam current due to the following possible processes; a decrease in the cathode drop, rotation of the plasma column, and induced instability in the source plasma. The potential depression in the source plasma due to extraction is analyzed with a simplified model and the experimentral results are discussed. © 1979 The Japan Society of Applied Physics.