Aluminum coating in the undulator vacuum chamber for the Linac Coherence Light Source

A prototype vacuum chamber is under development at the advanced photon source that is intended for use in the linac coherent light source at Stanford linear accelerator center. The chamber will be fabricated from the austenite stainless steels. The chamber requires a continuous aluminum coating on the inner surface in order to reduce the wakefield losses to a level within the resistivity budget. The method being presented here is unique in that it can be applied to a fully fabricated chamber 5 mm high, 12.5 mm wide, and 3460 mm long. In existing methods the chamber aperture has been much larger than is used here. This paper describes a method applicable for these smaller cross sections. This process uses a pair of small electrodes, centered in the aperture, where they are attached to a high-frequency AC power supply. In this configuration each electrode is connected to the opposite polarity of the other. The chamber cavity is filled with argon gas to facilitate the formation of a glow discharge causing the aluminum electrodes to sputter onto the chamber walls. This paper presents the laboratory test results from small samples up to the full- sized assemblies.