Introduction  High energy, strong current, and long pulse neutral beam negative ion source technology are one of the core technologies for achieving combustion conditions in magnetic confinement fusion reactor plasma. To meet the beam diagnostic requirements of the long pulse high-power negative ion source experimental platform under the parameters of 200 kV/20 A, a calorimeter target has been developed for intercepting negative ion beams or neutral beams, diagnosing the power density distribution and beam divergence angle of the two beams, as well as the neutralization efficiency of negative ions and other performance parameters.

  Method  Based on the existing structure of the experimental platform vacuum chamber and the size of the extraction electrode, the Matlab program was used to obtain the power density distribution and beam spot size of the negative ion beam generated by the negative ion source at the front end of the calorimeter target at a beam divergence angle of 1° under this parameter. Subsequently, the physical structure of the calorimeter target with a V-shaped target plate was designed. On this basis, Workbench software was used to simulate the thermal load of the oxygen-free copper V-shaped target plate structure under full power operation and obtain the temperature distribution of the calorimeter target during long pulse operation with a water flow rate of 80 m³/h. The highest temperature was 610 °C.

  Results  Based on the simulation calculation results, and in combination with the engineering structure and diagnostic requirements of the experimental platform, the engineering design of the calorimeter target was completed.

  Conclusion  The calorimeter target adopts magnetic fluid vacuum sealing to achieve the opening and closing of the V-shaped target plate, and a thermocouple array is arranged on the back of the target plate to monitor the temperature of the target plate in real time. The calorimeter target engineering has a compact structure, and its installation size can be compatible with ion beam diagnostic vacuum chambers and neutral beam diagnostic vacuum chambers, meeting diagnostic requirements and enabling safe operation with long pulses.