Effect of a biased probe on the afterglow operation of an ECR4 ion source

Various experiments have been performed on a 14.5 GHz ECR4 in order to impr ove the ion yield. The source runs in pulsed afterglow mode, and provides c urrents similar to 120 e mu A of Pb27+ to the CERN Heavy Ion Facility on an operational basis. In the search for higher beam intensities, the effects of a pulsed biased disk on axis at the injection side were investigated wit h different pulse timing and voltage settings. No proof for absolute higher intensities was seen for any of these modifications. However, the yield fr om a poorly tuned/low-performing source could be improved and the extracted pulse was less noisy with bias voltage applied. The fast response on the b ias implies that increases/decreases are not due to ionization processes. A good tune for high yield of high charge states during the afterglow coinci des with a high plasma potential. (C) 2000 American Institute of Physics. [ S0034-6748(00)59702-0].