Preparation and comparative testing of advanced diamond-like carbon foils for tandem accelerators and time-of-flight spectrometers

The sputter preparation technique for thin diamond-like carbon (DLC) foils, advantageously used for ion-beam stripping and timing in accelerator exper iments, has been optimized to improve the quality and the performance of th e foils. Irradiation lifetimes of 5 mu g/cm(2) DLC foils prepared by this t echnique have been compared with those for foils of approximately the same thickness, prepared by laser plasma ablation and for ethylene cracked foils when bombarded by 11 MeV Cu- - and Au--ion beams of similar to 1 mu A beam current at the Heidelberg MP-tandem. Standard carbon arc-evaporated foils were used as references. In these experiments, DLC stripper foils appeared to have a mean lifetime approximately two times longer than ethylene-cracke d foils regardless of ion species, and compared favorably with foils prepar ed by laser ablation method. All these foils lasted at least, 10 times long er than standard carbon foils, when irradiated in the MP terminal. Approxim ately, the same improvement factor was confirmed with 3 mu g/cm(2) DLC stri pper foils irradiated with 7.3 MeV Ni-beams at the Pelletron accelerator in Lund. Unlike standard carbon foils, most of the advanced lifetime foils ex hibited thinning during long irradiation, under clean vacuum. This suggests that sputtering of the foil by the heavy-ion beam might be a dominant proc ess, responsible for the observed failure of these long-lived strippers. Al ong with specifically corrugated self-supporting DLC beam strippers, we suc ceeded in the fabrication of very smooth and ultra thin (similar to 0.5 mu g/cm(2)) DLC foils, mounted on grids and used as start foils for the ToF sp ectrometers applied in ion beam analysis. (C) 1999 Elsevier Science B.V. Al l rights reserved.