Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 51 (2018)

Cooling down test of prototype accelerator system based on SC-QWR
K. Ozeki,∗1 O. Kamigaito,∗1 N. Sakamoto,∗1 K. Suda,∗1 Y. Watanabe,∗1 and K. Yamada∗1
The construction of a prototype accelerator system
based on the superconducting quarter-wavelength resonator (QWR)1–3) was completed in March 2017. Subsequently, cooling down tests of the system and excitation tests of the QWR were conducted for a number oftimes. In this contribution, the results of the cooling
down tests are reported.
Figure 1 shows an overview of the prototype accelerator system (cryomodule) seen from the beam axis. Athermal shield, which is made of aluminum and enfoldedby super insulation, is installed just inside the vacuumvessel. The thermal shield is cooled down using a cryocooler, SHI CH-110L.4) In order to cut oﬀ vibration of
the cryocooler, the cryocooler and thermal shield had
been connected using thermal contact wires that consist of oxygen-free copper braid wires. A medium suchas Apiezon-N or indium had not been applied on thecontact faces between the thermal contact wire and thecryocooler or thermal shield.
As a result of the test, liquid helium was ﬁlled up to ahelium buﬀer tank, and the excitation of the QWR ata cryogenic temperature was successful. However, wefaced a problem in that the temperature of the thermal
shield was much higher than expected. While the cryocooler is cooled to below 30 K, the temperature of thebottom of the thermal shield, which was connected directly to the cryocooler via the thermal contact wires,
was approximately 70 K. At the design phase of thecryomodule, we had assumed the temperature of thethermal shield to be 40 K. Possible causes for the muchhigher temperature of the thermal shield are as follows:
the thermal contact resistance at the contact faces was
too large, or the thermal conduction of the thermal contact wires was too small. At the design phase, theseelements had not been estimated suﬃciently. The thermal conduction between the cryocooler and the thermal
shield must be improved.
In order to obtain information for the improvement, acooling test of the thermal contact wire was performed.
The setup of the test is shown in Fig. 2. An aluminumplate, which simulated the thermal shield, was connected to the cryocooler via a thermal contact wire. Aheater was attached to the aluminum plate. By varying the heater power, temperatures at various points
were measured with several conditions of the thermal
contact faces: no medium, Apiezon-N, and indium.
The application of Apiezon-N showed the best thermal conduction, but it did not show a drastic improvement compared with no medium. More importantly, it
was found that the temperature diﬀerence between thetwo ends of the thermal contact wire was very large.
This fact suggests that the thermal conduction of the∗1

RIKEN Nishina CenterFig. 1. Overview of the cryomodule.

Fig. 2. Setup of the cooling test of the thermal contact wire.
The entire system was installed in a vacuum chamber.

thermal contact wire itself is not good. Based on thisresult, a reﬁnement of the structure and an increase of
the number of thermal contact wires are being considered for better thermal conduction.
This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Ofﬁce, Government of Japan).
References
1) N. Sakamoto et al., Proc. SRF2015 (Whistler, Canada2015), p.976.
2) K. Ozeki et al., Proc. LINAC16 (East Lansing, Michigan,2016), p.598.
3) K. Yamada et al., Proc. LINAC16 (East Lansing, Michigan, 2016), p.939.
4) http://www.shicryogenics.com/products/specialtycryocoolers/ch-110-77k-cryocooler-series/- 131 -