Hardware developments and commissioning of the imaging heavy ion beam probe at ASDEX upgrade

The imaging heavy ion beam probe (i-HIBP) is a new diagnostic concept realized at the tokamak ASDEX Upgrade (AUG) in order to obtain two-dimensional information about the density, the magnetic field and the electrostatic potential at the plasma edge. Although the two main components of the i-HIBP, an alkali beam based injector and a scintillator based detector, involve well-developed technologies, further developments were necessary to realize the i-HIBP at AUG. In dedicated laboratory tests, a new type of cesium source was characterized and the neutralization efficiency and properties of the primary cesium beam were found to be similar to alkali beams made of lighter elements. The use of cesium had also impact on the choice of the scintillator material, which was experimentally investigated in terms of photon yield, energy dependence and degradation revealing significant differences under irradiation with cesium ions compared to irradiation with hydrogenic beams. Due to constrictions of the AUG experiment setup, the high voltage components, the in-vessel shutter technology and the maintenance capabilities of the i-HIBP required new developments for the commissioning of the diagnostic.