Kenji Saito

Professor of Physics


  • Joined the laboratory in April 2012
  • Accelerator physics
  • Contact information

Education and training

  • BS, Mathematics and Physics, Ritsumeikan University, 1977
  • PhD, Nuclear Physics, Tohoku University, Japan, 1983


The 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 systems use 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 new areas of particle physics. The FRIB Project at
MSU utilizes this system for a major part of the accelerator.
I joined FRIB graduate school education program serving
as the FRIB SRF development manager since 2012.

The main part of an SRF system is the so-called cryomodule
and RF system. A cryomodule consists of a 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. A 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
a concern and 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 a high
gradient SRF cavity shape with an acceleration gradient
> 50MV/m and demonstrated the high-performance,
which is a world record so far. This activity will applied
other new SRF systems.

The SR cavity performance subjects to very shallow
surface characteristics where the RF surface current
flows. Particle/defect free clean surface is especially
crucial. Chemical clean surface preparation and clean
assembly technology are key technologies. I have
developed electropolishing method for elliptical shaped
the SRF cavity and confirmed it is the best process for
high gradient cavities. This technology will be applied to
low beta cavities and push the gradient in order to make
the SRF system more compact.

Cryostat design includes lots of engineering and material
issues. We are investing a lot on this subject in ongoing
FRIB cryomodule. The RF system is another 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, would make for a great theme
for a thesis. Thus the SRF systems cover 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.
The SR system is an exciting place to study. Any students
from physics, chemistry, materials, and mechanical/
electric engineering are welcome to join this project.

Scientific publications