NEUTRALIZATION OF SPACE-CHARGE FORCES USING IONIZED BACKGROUND GAS

The Tandem Van de Graaff at Brookhaven National Laboratory has deliver ed pulsed gold beam to the Alternating Gradient Synchrotron (AGS) and AGS Booster since 1992 for relativistic heavy ion physics. There is an ongoing effort to improve the quality and intensity of the negative i on beam delivered to the Tandem from the present Cs sputter sources. B ecause the beam energy is low (approximately 30 keV) and the current h igh, there are significant losses due to space charge forces. One of t he ways being explored to overcome these losses is to neutralize the s pace charge forces with ionized background gas. On an ion source test bench, using three different gases (Ar, N-2, and Xe), the percentage o f current transported from the source to a downstream Faraday cup was increased from 10% to 40% by bleeding in gas. Bleeding in Xe resulted in the best transmission. The time dependence of the neutralization as a function of gas pressure was also observed. This system is presentl y being transferred to the Negative Ion Injector of the Tandem for use in upcoming heavy ion experiments. (C) 1996 American Institute of Phy sics.