Heavy ion beam probe coordinate mapping and calibration at WEGA stellarator.

The heavy ion beam probe (HIBP) is an established nonperturbing diagnostic for high spatially and temporary resolved measurements of magnetically confined plasma parameters such as potential, density, and temperature. These quantities can be determined from the change in the ion beam parameters (charge, intensity, and trajectory) passing through a plasma volume due to collisions with electrons and interaction with the confining magnetic field. One of the problems that should be solved during HIBP installation and tuning is the coordinate matching. Conventionally the coordinate mapping of the HIBP measurement point is provided by ray tracing calculations of the ion beam in the magnetic field. However, it is very difficult to include all physical effects and uncertainties in the model. Thus, the result of the calculations may differ from the real probing position. In order to improve the mapping precision of the HIBP installed at the WEGA stellarator an additional measurement of the beam position is provided using a primary beam detector array inside the vacuum vessel. This allows comparing the measured and calculated ion beam positions in order to prove the calculated coordinate precision and include adjustments in the calculation code if necessary. The principle and the results of this calibration, which is not specific to WEGA but could be adapted to other experiments as well, are presented in this work.