Optimum thickness of carbon stripper foils in tandem accelerator in view of transmission and lifetime

Optimum thickness of charge stripper foils installed at the terminal of a tandem accelerator has been investigated from the view of (1) charge stripping effect, (2) transmission of ions through accelerator, (3) lifetime of foils for the irradiation of ions. For this purpose, measurements have been done for (a) transmission of H, Li, O, Br and Au ions, passing through 12 UD Pelletron tandem accelerator for carbon stripper foils of 1.8–19.5 μg/cm2 thickness, at terminal voltages of 5 and 10 MV, and (b) lifetime of 2–15 μg/cm2 thick Tanashi foils developed by Sugai by irradiating Au ions at the terminal voltage of 10 MV. The results obtained are as follows: (a) From the view of above items (1) and (2), the optimum thickness of foils is 10 μg/cm2 for ions of Z=1, several μg/cm2 for Z=8, and less than a few μg/cm2 for heavier ions. (b) From the view of item (3), the lifetime of Tanashi foils by means of new arc-discharge method is demonstrated to be much longer than that of commercial foils for foils thicker than about 5 μg/cm2 thick. This superiority rapidly decreases with decreasing foil thickness, and at around 2 μg/cm2, the lifetime of Tanashi foils is at the most 2.4 times longer than that of commercial foils.