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Our Nb accelerating cavity vertical electropolishing (VEP) facility development group which was led by KEK started single-cell VEP facility development from 2014. This is based on KEK’s over 10-year horizontal electropolishing (HEP) techniques and Marui’s over 30year stainless steel electropolishing techniques. We have reported results of Nb cavity VEP with Ninja cathode so far. In order to achieve international linear collider (ILC) construction, it is said that cost reduction and productivity improvement are necessary, however in case of 9-cell cavity, uniform inner surface polishing is difficult, as well known to predecessors. In this article, we will report the first report of VEP facility development from initial mockup to improvement for Nb 9-cell cavity. REGARDING ELECTROPOLISHING 4M Our 9-cell VEP development points are based upon know-how gained in over 30 years of experience with stainless steel electropolishing. In contrast with HEP, which has an over 15-year track record with Nb material, our development of a VEP system started from scratch. We began by laying out the basic points of electropolishing. The following points are essential in achieving uniform electropolishing. 1) Basic Elements a) Agitation of the sample b) Management of the EP solution flow c) Management of the current d) Build optimal cathodes for target material. The above 4 items may be called the 4M of electropolishing. 2) Why are the 4M necessary? Based on our many years of experience, unlike electroplating, electropolishing work requires a viscous film and viscous layer. 3) We hypothesized that a satisfactory electropolishing cannot be achieved without creating a viscous film in the initial stages of the electropolishing. But this viscous layer also becomes a factor in the flow of hydrogen bubbles. If this viscous layer is not controlled, the optimal electropolishing goal cannot be achieved. It is for that reason that we summarized the 4M of electropolishing based on our years of experience in the industry. With the formation and workings of this viscous layer in mind, and based on the 4M of electropolishing, our researchers undertook development of the 9C VEP. OBSERVATION OF SACLAY, DESY, CORNELL, JLAB, AND INVESTIGATION INTO VEP POSSIBILITY In 2011, I read about Japan’s ILC in the newspaper. At that point, our company had about 25 years of experience in electropolishing, but we knew nothing about Nb cavities. They had experience electropolishing stainless steel, and aluminum but it was the first time I’d heard of the alloy Niobium. As a provider of electropolishing services, I was interested, so I contacted KEK, the originator of the newspaper article, and asked if I could visit them and observe. They had experience doing electropolishing of stainless steel accelerator cavities as at J-PARC. Observing their onsite Nb cavity electropolishing made us very interested, and we suggested doing collaborative research with KEK’s Dr. Hayano. Afterwards, we became curious about the state of affairs with electropolishing overseas, and so with the introductions from Dr. Hayano, we visited France’s Saclay, Germany’s DESY, Italy’s Zanon, America’s Cornell, and America’s JLab. All of the places we visited were using the HEP (Horizontal Electropolishing System) introduced by KEK. As an electropolishing provider, when I learned this fact, I had many questions: Was the distance between the cathodes proper? How was the circulation of the electropolishing solution? Was it really the best for this new shape to use horizontal electropolishing? My first impression was that if it were me, I would want to do the electropolishing of this kind of target using a vertical process. This was due to my experience in electropolishing the inner surface of stainless steel Sshaped and U-shaped valves. But it wasn’t until I first did electropolishing on a single Nb cell that I realized that my 25 years of experience with stainless steel couldn’t be directly applied. PRODUCTION OF THE NINJA CATHODE BASED ON STAINLESS STEEL CAVITY RESERCH In 2013, when we first began to experiment, we were able to borrow a transparent resin model of a 9-cell cavity. Using that model, we first looked into the issues of the EP solution flow and cathode shape [1]. As an electropolishing company, we are very exacting about maintaining a uniform distance between the target sample and the *yoshiaki_ida@e-marui.jp 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPAL031 07 Accelerator Technology T07 Superconducting RF THPAL031 3699 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I.

Development of a Vertical Electropolishing Facility for Nb 9-Cell Cavity