Tomohiro Koyama

Measurement of vibration of the top of the suspension in a cryogenic interferometer with operating cryocoolers

In the LCGT and CLIO projects for the interferometric gravitational wave detectors of Japan, the mirrors and a part of the suspension systems are cooled by cryocoolers to reduce the thermal noise. For the CLIO, extremely small vibration cryocoolers were specially developed by improving a commercial Gifford-McMahon type pulse tube cryocooler. We measured the vibration at the top of the suspension base in the CLIO interferometer while operating these cryocoolers. Although the seismic motion of 10−9(1 Hz/f)2 m/Hz½ at the site of the CLIO and LCGT in the Kamioka mine is 100-times smaller than that around Tokyo, these cryocoolers did not seriously increase the vibration. Consequently, a reduction of thermal noise by the cooled mirrors and suspension fibers using these cryocoolers is expected to be observed without any additional fluctuation disturbance due to the cryocoolers.

Vibration-Free Pulse Tube Cryocooler System for Gravitational Wave Detectors, Part II: Cooling Performance and Vibration

A vibration-free pulse tube cryocooler system has been developed for gravitational wave detectors. A commercially available 4 K pulse tube cryocooler (SRP-052A, Sumitomo Heavy Industries, Ltd.) with a cooling capacity of 0.5 W at 4.2 K was applied in the system. In order to reduce the vibration of the 4 K pulse tube cryocooler to an ultra low level: (1) two vibration reduction stages (VR stages), (2) a cold head supporting frame, and (3) a valve unit mounting table were introduced as major components of the system. The cooling capacities of 15 W at 45 K and 0.4 W at 4.2 K were available at the first and the second VR stages simultaneously. Concerning the vibration, on the other hand, the displacement due to the elastic deformation of the pulse tubes was effectively reduced to be less than ±1 µm. In the direction parallel to the pulse tubes, the displacement was lowered to ±0.05 µm, which is two to three orders of magnitude less than that of the original 4 K pulse tube cryocooler, SRP-052A.

Development of a cryocooler vibration-reduction system for a cryogenic interferometric gravitational wave detector

We have developed a pulse tube cryocooler vibration-reduction system for a cryogenic interferometric gravitational wave detector, based on an experimental vibration analysis for commercial 4 K cryocoolers. In a preliminary test, the vibration of the cold stage was reduced by two orders of magnitude using this vibration–reduction system.