In-Situ, Large-Area, Conformal, Superconductive RF Coatings & Surface Cleaning Via IMPULSE HiPIMS & Positive Voltage Reversal

In a recent report from a 2019 DOE Workshop on Compact Particle Accelerators for Security and Medicine, critical research needs were outlined that, if the challenges can be surmounted, will enable a new generation of compact particle accelerators having a wide range of applications benefiting both to the American public and to the scientific community at large. These applications include wastewater, sludge and medical waste treatment, medical sterilization, non-invasive inspection of cargo containers, and chemical reaction catalysis. This list is far from exhaustive. One of the key challenges identified in the DOE workshop is the present lack of a capability to apply high-quality, conformal, superconductive radio frequency (SRF) coatings over large areas and to objects with complex surfaces. To surmount this challenge, Starfire Industries has developed a new technology utilizing next-generation plasma sputtering to coat large and complex objects. The Phase I effort involved investigating and de- risking the major risk items associated with using this technology for SRF coatings developing high- speed power electronics that have been integrated into Starfire’s existing line of IMPULSE® products and commercially deployed to customer sites. The Phase II effort will build on this effort by demonstrating the technology on a resonator cavity that is typical of a modern particle accelerator. In Phase I, Starfire demonstrated 1) high-speed electronics required for achieving conformal sputtered coatings with minimal particulates or defects, 2) in-situ discharge cleaning (for surface modification & preparation) using Starfire’s IMPULSE® w/ Positive Kick™ a specially designed radial magnetron, 3) large area conformal coatings of copper using the high-speed electronics and in-situ discharge cleaning, and 4) established baseline superconductive film depositions and a quick-turnaround process for RF film characterization at cryogenic temperatures. The Phase II effort aims to leverage the technology de-risking from Phase I to produce a Nb-coated copper SRF cavity having an RF performance that is competitive with bulk Nb. Specifically, the specialized radial magnetron design demonstrated in Phase I will be extended to sputter Nb films, which will be used in conjunction with the high-speed electronics and quick-turnaround RF characterization to rapidly iterate through the film development process. Periodic testing of coated-copper SRF cavities at the Thomas Jefferson National Accelerator Facility (JLab) will be used to further guide this development over the course of the Phase II effort. This technology will enable lower cost accelerators, with decreased power consumption, reduced size, and higher efficiency, with potential crossover into high-temperature superconductor (HTS) manufacturing. The technique will also support industrial normal conducting accelerators (operating at RF frequencies of e.g. 600-700 MHz) in order to provide low cost, reliability, and long-term stable operation. The resulting marketable product will be an SRF cavity-coating system, developed in cooperation with the Kurt J. Lesker Company, a key distribution and marketing partner. The coating system will employ both the IMPULSE® 20-20 pulsed power module and Starfire’s serpentine-racetrack cylindrical magnetron sputter cathodes.