PURPOSE: To enable precise measurement of a large cavity loss in a short time by providing a cryostat with a guide box which collects bubbles generated from a superconducting cavity provided in a cryogen in the cryostat.
CONSTITUTION: A guide box 7 is so disposed as to surround a superconducting cavity 3 in liquid helium 2. The box 7 has a structure in which bubbles generated from the cavity 3 are collected without allowing them to escape. The structure prevents vapor from entering from a microwave line 5, the bottom surface 2a of a cryostat and the lateral surface 1b thereof. Besides, the upper part 7c of the guide box is shaped in a funnel so as not to allow the gas to stay. The upper part 7c of the box is connected with a transfer pipe 8 for taking out a helium gas, and the transfer pipe 8 extends from inside to outside of the cryostat 1 through a top flange 6. The temperature of the helium gas in the transfer pipe 6 rises to a room temperature while the gas flows through the transfer pipe 8 outside. The gas enters a gas flowmeter 9 and the flow rate thereof is measured. According to this constitution, a cavity loss, i.e., a Q value, can be measured precisely.
SHIMANO TAKASHI
SAKANO MISAO
