Transmission Measurements for Heavy Ion Beams through the Rochester MP Tandem

The transmission efficiency for heavy ions through the MP Tandem Van de Graaff at the University of Rochester has been measured for 16O, 32S, 58Ni, and 197Au at terminal voltages of 8 MV, 10 MV and 10.5 MV using gas stripping and high-speed cryogenic terminal pumping. For oxygen the transmission was close to 100%; for 197Au the transmission over the range of terminal voltage 8-10 MV was between 25 and 50%. No significant beam loading was measured when 4 ??A of 197Au were injected, and there was no indication of a current limit at this intensity level. A comparison of the data with theoretical charge state distributions show that multiple scattering losses in the terminal were not significant and that the vacuum in the high energy acceleration tubes was adequate.