High heat flux testing for W/Cu monoblock PFUs with varying defects

Abstract

The full tungsten divertor is the key component of Experimental Advanced Superconducting Tokamak (EAST) to exhaust excessive heat loads. After EAST discharge operation, defects may appear in the tungsten/copper (W/Cu) joints of W/Cu monoblock plasma-facing units (PFUs). In order to evaluate the heat removal capability and thermal fatigue stability of W/Cu PFUs with defects, the specific heat treatments are used for PFUs to introduce defects of varying degrees. Then, high heat flux (HHF) tests for PFUs with defects are performed on a 100 kW electron-beam (e-beam) device at ASIPP. The W/Cu joints defects and W surface conditions have no significant differences after HHF tests. And the test results show that the fewer defects or the larger water mass flow is, the better heat removal capability of the W/Cu monoblock has. The surface temperature of W/Cu PFUs with major defects (> 2 × 3 mm) is 12% - 17% higher than that of PFUs with minor defects (≈ 2 × 3 mm), and the minor defects PFUs is 6% - 8% higher than the non-defects one (< 2 × 3 mm). Besides, the temperature curves of three W/Cu PFUs are exponentially fitted in cooling down phase, and the obtained average thermal decay time constants are 11.1 s, 8.5 s and 7.4 s, respectively. The time constants quantitatively explain the cooling performance of PFUs with various defects, and provides a feasible method for non-destructive inspection of PFUs defects during EAST experiment. These results are conducive to understanding the relationship between damage degree and heat transfer performance, and can provide relevant basis for improving the acceptance criterion of qualified W/Cu PFUs.