Thermal mechanical characteristics research of HL-2M vacuum vessel during baking

Abstract

The medium-sized tokamak HL-2M has been built in Chengdu and get its first plasma in December 2020. The vacuum vessel was assembled and passed the 1 MPa pressure tests and the preliminary vacuum tests at the SWIP in 2019. To get a high quality vacuum condition, vacuum vessel and in-vessel components should be baked up to check the quality of all welds and remove all water vapor in the material. Due to baking the non-uniform temperature pattern on the vessel coupled with atmospheric pressure loading and self-weight give rise to high thermal-mechanical stresses, which needs to be analyzed in detail. Pre-baking should heat vacuum vessel up to 100–120 °C, the thermal insulation layers(micro porousmaterial) were applied on the outer surface of the vessel to reduce the heat loss. The surface temperature distribution of vessel was measured by thermocouples and displacement was measured by potentiometer and laser displacement sensors. The pre-baking experiments show that the temperature and displacement distribution over the vessel wall are with100±10 °C and ±2 mm. During natural cooling, it is predicted that the time constant τc of vacuum vessel is about 20 h and the total heat loss power is about 34 kW. The pre-baking experiment provides support for the safe operation of HL-2M device, and provides valuable experience for the future induction baking or high temperature baking experiment.