Yuki Ikushima

Vibration-Free Pulse Tube Cryocooler System for Gravitational Wave Detectors, Part I: Vibration-Reduction Method and Measurement

We developed a vibration-free cryocooler system based on a 4 K pulse tube (PT) cryocooler for a cryogenic interferometric gravitational wave detector. In this system, we incorporated a vibration-reduction system that consists of a firm support for the cold head and a rigid cold table thermally linked to the cold stage to reduce both the vibrations of the overall cold head and those of the cold stage. Our cryocooler system reduced the cold-head vibration of the baseline PT cryocooler by over three orders of magnitude, where the vibration level was on the order of \( 10^{ - 9} /f^2 m/\sqrt {Hz}\).

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.

Ultra‐low Vibration Pulse Tube Cryocooler with a New Vibration Cancellation Method

The vibration of the cold stage of model cryocoolers was measured for proving a method of vibration cancellation. A model cryocooler consists of multi‐pairs of pipes on the same cold stage. When a presented working gas is supplied with a proper phase shift to those pairs, the vibration of the cold stage can be cancelled. We made models of the PT cryocoolers with a single pipe, two pairs of pipes and three pairs of pipes. Compared with the single‐pipe model, the six‐pipe model shows about a 98% reduction of vibration without any additional structure for vibration isolation.

SMALL VIBRATION CRYOCOOLER SYSTEM FOR CRYOGENIC GRAVITATIONAL WAVE INTERFEROMETER

An ultra-small vibration cryocooler system for a cryogenic interferometric gravitational wave detector has been developed. The system consists of a pulse tube cryocooler and a vibration-reduction system. Its vibration level was about 50 nm for the vertical direction at 1 Hz, which was three orders of magnitude smaller than that of an original pulse tube cryocooler.