A new UHV system for the preparation of carbon stripper foils by laser plasma ablation deposition

Abstract

Laser plasma ablation of spectroscopically pure graphite under UHV conditions is a well established method for the preparation of thin carbon stripper foils. Such foils with their structure of randomly oriented nanocrystallites can best withstand ion irradiation damage. Accelerator users around the world are interested in this type of carbon stripper foils due to a guaranteed reproducibility, quality, thickness and uniformity given by the procedure. In addition a high reproducible yield with a low effort for floating, mounting and slackening is desired. Users of high-energy accelerators want to profit from this development, but need stripper foils of up to 500 μg/cm 2 for the relevant charge state equilibrium whereas carbon foils of this type could only be prepared with an upper limit of 10 μg/cm 2 in the existing set up. The new design was aimed to overcome all thickness limitations. The crucial component of the laser plasma ablation technique is the laser entrance window which becomes opaque during carbon ablation. A new plant which overcomes this problem is being assembled. Due to a higher source-to-window distance and a better laser light transmission, caused by slightly changed laser plasma conditions, the life of the laser entrance window before exchange could be prolonged by a factor of five. Presumably, there are no thickness limitations anymore due to a vacuum interlock that permits the exchange of the entrance window without breaking the vacuum in the ablation-deposition chamber.