Accelerator is the base tool for nuclear physics, high energy physics, light sources, medical applications, and so on. Superconducting Radio Frequency (SRF) Systems are an application of microwave acceleration for ion beams. The principle is the same as normal conducting RF system but SRF system uses superconducting technology, which allows high quality beam acceleration with very high efficiency. It is a key technology for current world-wide accelerator projects for nuclear science and high energy physics. SRF systems are a state-of-the art technology to open the new areas of particle physics. The FRIB project at MSU utilizes this system for a major part of the accelerator. I joined the NSCL graduate school education program servicing the FRIB SRF department manager in 2012. My profile photo shows a quarter wave resonator (80.5MHz) and have wave resonator(322MHz) for FRIB.
The main part of a SRF system is the so-called cryomodule and RF system. Figure 1 illustrates the FRIB beta=0.53 half wave resonator cryomodule. Cryomodule consists of cryostat and SRF cavities included therein. Ionized beam is accelerated by SRF cavities, which is made of superconducting material and cooled by liquid helium at below 4.2K. Cryostat is a kind of Thermos bottle to keep SRF cavities at such a low temperature. Niobium material has been utilized for SR cavities, which has high quality superconducting features: higher superconducting transition temperature Tc=9.25K and higher thermodynamic critical field Hc = 200mT. Niobium has a good forming performance to fabricate cavities. Development of high quality niobium is always concerned. I have been working on high purity niobium material. My latest concern is single crystalline niobium ingot or other new materials.
In RF cavity design it is very important to have an excellent SC cavity performance, which has to be simulated intensively by specific computing cords. I have developed high gradient SRF cavity shape with an acceleration gradient > 50MV/m and demonstrated the high performance, which is world recorded so far. This activity will be applied to other new SRF systems.
SR cavity performance subjects to very shallow surface characteristics where RF surface current flows. Particle/defect free clean surface is crucial. Chemical clean surface preparation and clean assembly technology are key technologies. I have developed electropolishing method for elliptical shaped SRF cavity and confirmed it is the best way for high gradient cavities. This technology will be applied to low beta cavities and push the gradient in order to make compact SRF system.
Cryostat design includes lots of engineering and material issues. We are investing a lot of investing issue on this subject in ongoing FRIB cryomodule.
The RF system is other exciting place to study. Concerning SRF, high power coupler is an important issue to develop. The design of multipacting free high power coupler structure and cleaning technology, TiN coating technologies are good theme for a thesis.
Thus SRF system covers various sciences and super-technologies: electromagnetic dynamics, superconducting material science, plastic forming technology, ultra-clean technology, ultra-high vacuum, cryogenics, RF technology, mechanical/electric engineer. SR system includes is an exciting place to study. Any students from Physics, Chemistry, Materials, and Mechanical/Electric Engineer are acceptable for this subject.
Selected PublicationsState-of-the-Art and Future Prospects in RF Superconductivity, K. Saito, 2012 International Particle Accelerator Conference (2012)
Multi-wire Slicing of Large Grain Ingot Material, K. Saito et al., the 14th Workshop on RF Superconductivity 2009 (SRF2009)
Gradient Yield Improvement Efforts for Single and Multi-Cells and Progress for Very High Gradient Cavities, K. Saito, the 13rd Workshop on RF Superconductivity 2007 (SRF2007).
Theological Critical Field in RF Application, K. Saito, the 11th Workshop on RF Superconductivity SRF2003 (2003).
Superiority of Electropolishing over Chemical Polishing on High Gradients, K. Saito et al., The 8th Workshop on RF Superconducivity (1997).