A new long-pulse diagnostic calorimeter for the negative ion source testbed ELISE

The RF-driven negative ion source testbed ELISE at IPP Garching is being upgraded to allow for long-pulse beam operation, previously limited to 10 s beam pulses every 150 s. The improvements aim to extend the beam phase duration up to 1000s in H and 3600 s in D, in the framework of the ion source development for the ITER and DEMO NBI systems. The main upgrades comprise a recently commissioned steady-state HV power supply and a new long-pulse, actively cooled diagnostic calorimeter. The latter is made of copper plates with a total beam power measuring surface of 1.2 m x 1.2 m, placed at about 2.9 m from the ion source extraction grids. With respect to the previous inertially cooled beam dump, the new calorimeter has been designed to withstand a higher power load of up to 1.8 MW (maximum power density of 5 MW/m2) in continuous operation and with a higher spatial resolution (2400 points, spaced 30 mm H x 20 mm V) for 2D profile evaluation of beam power density. The measurement is enabled by small apertures (o2 mm) in the copper plates that let a fraction of the beam pass through to be collected by thin (0.2 mm) copper "heat flux foils" attached to the back side of the plates. The power density evaluation is performed by mapping the temperature gradient in the heat flux foils with a high-resolution infrared camera, observing the calorimeter from the back side, which is calibrated by thermocouples attached to the copper plates. Cooling channels embedded in the calorimeter plates are arranged in 8 separate circuits, each equipped with individual water calorimetry measurements for additional beam power evaluation capability. This paper describes the design, manufacturing and commissioning of the new long pulse calorimeter for ELISE.