The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

A COMPACT CLOSED LOOP 2K He 3 REFRIGERATOR AND ZERO-BOIL-OFF CRYOSTAT DESIGNFOR THE JAERI SUPERCON DUCTING RF LINAC-BASED FEL
E.J.Minehara, M. Sugimoto, M.Sawamura, R.Nagai, N.Kikuzawa and N.Nishimori
Free Electron Laser Laboratory, Department of Reactor Engineering,
Tokai Research Establishment,
Japan Atomic Energy Research Institute
2-4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki-ken, 319-11 JAPAN
Since an invention of a superconducting rf linac in1965, a less-efficient, complex, expensive and huge
cryogenic system circulating liquid He and N 2 coolant

frequency and exponential function of working
temperature, we have to reduce the resistance in the higher
frequency by lowering the cavity temperature down tomedia must be used to cool down cavities and heat shields around 2K or even lower. Here, we will report preliminaryof the linac. We also need a lot of specially-trained
results of the 2K 3He gas refrigerator and cryogenic
engineers and technicians for a domestic pressurized vessel measurement
s. The measurement set-up is shown in figs.
code-regulated devices like the linac in every country tol,and 2. In the set-up, cooling power was measured to be
run it safely and continuously except for the power failure,
about I W at 2.17K and He 3 gas flow rate of 2. 75Nm 3/h.
repairs and maintenance.
We have newly developed a zero-boil off multirefrigerators system integrated into the superconducting
accelerator module cryostats to realize a highly-efficientsystem without any liquid coolant and any maintenancecrew. A prototype of the system had a lot of troubles
related to the He gas compressor's heat exchanger andrelated parts in the beginning phase. After themodification related to the troubles in the beginning ofOctober1995, we can run all of the modules successfully
for about 11 months without any trouble. Each cryostat of
the new system has two independent refrigerators, each one
is designed to be independently structured, and powered. A
4K closed-cycle He gas refrigerator mounted just above aliquid-He supply tower of the module was adopted to cool
down and to recondense cold vapor of liquid He around aheat exchanger in the liquid He container. A 40K/80K
Fig.l, Photograph of the measurement set-up. 2K test
two-stage closed-cycle He gas refrigerator, which wascryostat and 2 compressors and 2 He 3 gas bottles
mounted in a vacuum vessel of the module was adopted tocool down the 40K and 80K heat shields and other major
components of the cryostats. The 40K and 80K heatshields are used to prevent heat invasion from outside into
the liquid He container. In order to minimize heat loads
to the container, the heat shields work as a thermal anchor,
and make the return route having a temperature higher thanthe liquid He temperature for all heat bridges from theoutside.
In the conference, we will also discuss about a newcryogenic design for the 2K cryostats and refrigerator
system of the superconducting rf linac with higher
accelerating field and frequency than 5MV/m and 500MHz,respectively. Up to now, no 2K recondenser refrigerator
has been available for the rf linac because of manytechnological difficulties related with a superfluidity ofFig.Z, Photograph of the 2K test cryostat. A 20K/80K
4 He. According to the BCS theory,
because surface
test cryostat heat shield cooler, feedthroughs and 2K He 3
resistance of the cavities is nearly proportional to square of refrigerator .

-236-