Design Updates and Installation Plans for a Heavy Ion Beam Probe on Wendelstein 7-X

A heavy ion beam probe (HIBP) diagnostic is being developed for the Wendelstein 7-X (W7-X) stellarator. It will contribute to understanding neoclassical and turbulent transport through measurements of equilibrium electric potential, radial electric field, and fluctuations of potential and density. Plans are to install the HIBP in two phases. During W7-X maintenance phase 2.4 (MP2.4), the secondary beamline, energy analyzer, and platforms to support the diagnostic will be installed. During MP2.6, the rest of the diagnostic will be installed. Testing will be conducted during the W7-X operation phases between MP2.4 and MP2.6. The current load caused by plasma ultraviolet light on beam steering electrodes will be determined. This information is needed to finalize the steering system designs. Other tests will determine whether modifications are needed to maintain a voltage of 300 kV on the energy analyzer’s anode. A key and recent design modification has reduced the distance between the anode and ground plane ~14% and accordingly lowered the maximum required anode voltage. This enables use of a more compact power supply and its installation in the torus hall. Simulations indicate that accuracy of measurements will not be adversely affected by this change, and additional modifications could improve the performance. Full operation of the HIBP is planned during the W7-X operation phase following MP2.6.

Funding Acknowledgement: This material is based upon work supported by the US DoE, OFES under award DE-SC0013918