Preparation and investigation of thick carbon foils prepared by laser plasma ablation deposition

Abstract

Carbon foils prepared by laser plasma ablation deposition using a power density of > 1 GW / cm 2 are so far the only ones which have been shown to have a total random orientation of the nanocrystallites and thus the theoretically best resistance against irradiation damage caused by ion bombardment. Need for longer lifetimes of carbon stripper foils was observed firstly in tandem accelerator experiments with heavy ions. There the required thickness is 3 to 10 μ g / cm 2 and the plant was developed to meet these needs. Thicker carbon stripper foils are required as dead-section strippers and post-strippers. For the stripping of H - beams in the GeV range thick ( > 100 μ g / cm 2 ) carbon stripper foils are required. The new plant which should facilitate the ablation deposition for this type of foils of unlimited thickness has been constructed. First results are presented about the preparation of thick ( > 50 μ g / cm 2 ) carbon stripper foils of this kind and the applicability of the results to the preparation of carbon stripper foils of several hundred μ g / cm 2 is discussed. For the application as gas detector windows very good chemical resistance is required if the carbon foil becomes hot due to the energy loss of the ion beam. Investigations for a 4 μ g / cm 2 laser plasma carbon foil window transmitting 10 p μ A of 3 MeV C 2 + 12 are reported. If very uniform electronic energy loss is required the corrugated structure, caused by the betaine parting agent on laser plasma carbon foils, is not suited. Therefore, it was tried to utilize release agents of different types of evaporated salt layers which were covered by 100 μ g / cm 2 copper in the same vacuum process. The floating success rates for those release agent combinations are reported.