Thermal analysis and experimental study of cryostat for superconducting wiggler of the HEPS-TF

•Cooling capacity distribution is feasible, where two cryocoolers condense helium vapor and the other two cool down helium tank surface.•A single thermal shield is enough for the interruption of thermal radiation in a 4K cryostat.•Zero helium consumption can be realized in the SCW cryostat with some residual cooling capacity.•Beam model can change the heat load and it should be modified to an ideal condition. As an insertion device, the superconducting wiggler has been developed for about 40 years, the superconducting magnet of which is usually made of NbTi and set in a cryostat. The performance of the cryostat is vital to the success of the superconducting wiggler. In this paper, a cryostat of the superconducting wiggler with 32 poles and 2.6 T field for the High Energy Photon Source Test Facility (HEPS-TF) was developed in the Institute of High Energy Physics (IHEP). In the cryostat, a novel design of thermal structure and cooling capacity distribution was proposed. Compared with the conventional two thermal shields, the single thermal shield was adopted to simplify the mechanical design, which was extended to the outside of the vacuum chamber to decrease the heat loads at 4.2 K. The current leads were optimized to minimize the heat loads at 60 K. After the systematic thermal analysis and optimization, the total heat load was covered by the four Gifford-Mcmahon cryocoolers successfully. In the experiment, the measured heat load was 3.85 W with magnet current of 320 A and beam of 250 mA. And the residual cooling power was 0.65 W.