Suppression of Thermal Oscillation Induced by Liquid-Nitrogen in the CESR-Type SRF Module

A superconducting radio-frequency module of CESR type serves as the accelerating cavity at the Taiwan Light Source (TLS) in the National Synchrotron Radiation Research Center. During its routine operation at TLS beginning in 2005, a strong correlation of the movement of the cavity's frequency tuner with the temperature variation of parts cooled with liquid nitrogen was observed. After comprehensive tests on a testing SRF module, satisfactory suppression of the thermal oscillation was achieved. A phase separator with pressure regulation supplied liquid nitrogen to the SRF module, and a thermally insulated buffer tank was installed between the SRF module and the warmer of the exhausted nitrogen. Regulation of either the flow rate of nitrogen or the pressure in the buffer tank improved the temperature stability with an appropriate setting. The motion of the frequency tuner resulting from the temperature fluctuation thereby became suppressed. Identical SRF modules are currently operated in other colliders and light sources such as CESR, CLS, DLS and SSRF; this work is thus essential to improve the operation performance of the SRF module of CESR type for accelerator application.