The Design of an Ion Beam Probe for Wendelstein 7-X and the Study of Optimized Stellarator Physics

The dynamics of particle and energy transport is particularly important to the physics of optimized stellarators. A critical need exists for experimental data that will complement the models used to estimate power and particle balance. A heavy ion beam probe (HIBP) diagnostic can help fulfill this need with its unique ability to acquire direct measurements of the electric potential, and fluctuations of electron density and potential in the plasma interior. We have developed a full concept design of a HIBP for Wendelstein 7-X (W7-X) and passed the critical conceptual design review milestone. The system will inject up to a 2 MeV singly-charged ion beam and is designed to access the outboard cross-section of all eight W7-X reference magnetic field configurations. The diagnostic will concurrently acquire measurements at three plasma locations that may be displaced: radially, enabling inference of the electric field; or poloidally on a flux surface, permitting measurement of wavenumbers. Fluctuation induced particle flux will be assessed from its measurement of amplitudes, cross-phase and coherence among density fluctuations and potential fluctuations. We will present: the results of recent efforts that have emphasized realizing a cohesive HIBP conceptual design, anticipated characteristics of measurements predicted via simulations of beams through W7-X plasmas, CAD schematics of the system, and opportunities for collaboration.