Insertion device vacuum chamber for the Linac Coherent Light Source

The vacuum requirement for the undulator line of the Linac Coherent Light Source is extremely challenging: a low resistive wall impedance 3.42-m-long chamber that fits within a 6.3 mm undulator gap that has ultralow outgassing and a surface finish, less than 100 nm Ra. A prototype chamber will be fabricated from electropolished semiconductor-processing-grade stainless-steel seamless tubing. Since stainless-steel tubing has a high electric resistivity, which can increase the resistive wall wake, a thin layer of copper will be deposited to minimize this effect. A thin nickel plating will be deposited in advance for better adhesion. This process will be followed by electropolishing of the copper surface. The first approach for Cu coating of the vacuum chamber has been investigated. Roughness measurements and preliminary coating results with a one-meter-long tube will be presented.