EFFICIENCY IMPROVEMENTS WITH A NEW STRIPPER DESIGN

A new stripper arrangement has been designed and installed in the existing EN tandem accelerator. The primary improvements were to move the foil stripper behind the gas stripper (instead of in front of it) and to equip the terminal with a turbomolecular pump to recirculate the stripper gas. The pump allows the use of a higher gas density in the stripper. At the same time the vacuum conditions were improved in the acceleration tubes. Technical details are given and the performance is discussed. The new stripper enables the EN to be operated under conditions which are near the optimal yield of carbon ions in the 4+ state. Under these conditions the efficiency of C4+ production is more than 70%. In first experiments, an overall transmission of about 50% was attained. For radiocarbon dating this is an improvement of almost a factor of two, compared to the previous performance. This allows an increased throughput or a higher accuracy with the same beam time. For radioisotopes other than C-14 foil strippers are used. With the new equipment and thinner C-foils (3-mu-g/cm2) the transmission for Be is now about 30%. For Al and Cl transmissions of about 18% and 14% were obtained, respectively.