Nickel-plated invar mirrors for synchrotron-radiation beam lines

摘要

We report the experience of the Advanced Light Source group in designing and building a series of nine electroless nickel-plated invar mirrors. The first four mirrors constructed appeared initially to be good but later it became evident that the nickel plating on all nine had been done improperly. The problem first appeared as blister-like defects about half a micron high and one to three centimeters wide. The cause turned out to be local separation of the plating from the substrate. In this paper we discuss the technical issues involved in building mirrors from invar and in preparing for and applying the needed electroless nickel coatings. We describe the studies that we carried out to evaluate the questions of adhesion, stress and polishability and report broad success in remanufacturing four of the mirrors. At time of writing one of the four has met specification showing good figure (0.8 μr rms) and finish (6 A rms).