Speaker
Description
A 50-period bulk high-temperature superconducting (HTS) undulator, utilizing a staggered-array configuration of RE-Ba-Cu-O bulk superconductors and magnetized by a 7 T solenoid magnet, is currently under development at Zhangjiang Laboratory for Shanghai Soft X-ray Free Electron Laser (SXFEL) facility [1-2]. The device operates through multiple temperature control stages for the HTS insert, including heating above the critical temperature, ~110 K, to transition out of the superconducting state, field-cooled (FC) magnetization at 10 K, flux freezing at 8 K and stable operation at 7 K. Achieving a homogeneous undulator field with minimal peak-to-peak field error necessitates the maintenance of a stable and uniform temperature distribution across the long HTS insert, imposing stringent demands on the temperature control system. The system was developed using Python, integrating Lakeshore controllers and 12 sensors for high-precision temperature monitoring, with resistive heaters mounted on the second-stage cold head of each GM cryocooler at both ends to facilitate regulated temperature control. By dynamically adjusting the PID parameters to align with the cooling power provided by the GM cryocooler, we successfully managed the temperature control sequence from 110 K to 10 K, 8 K and 7 K, achieving an accuracy better than ±0.01 K within the critical temperature range of 5 K to 15 K. The cold shrinkage of the long HTS insert along the electron beam direction was measured using high-precision displacement sensors, showing consistency with the calculated value. This study presents a detailed summary on the cryogenic test and high-precision temperature regulation of the 50-period bulk HTS undulator.
Key words: High-Temperature Superconducting Undulator, Temperature Control System, PID Control, Python-based Control System
References
[1] K. Zhang et al, 2025, IEEE Trans. Appl. Supercond., 35, 4100205
[2] D. Wei et al, 2024, IEEE Trans. Appl. Supercond., 34, 4100705
