Heavy Ion Beam Probe Design for Wendelstein 7-X and Projected Measurement Capabilities*

A need exists for additional experimental measurements that lend insight into neoclassical and turbulent transport in Wendelstein 7-X (W7-X), an optimized stellarator. 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. Such data will help to inform theoretical models that describe neoclassical transport and ion-scale turbulent transport. We have developed a system design of an HIBP for W7-X and are currently preparing for the developed design review. The design ensures that the HIBP will be capable of measurements from the core to the edge in the outboard cross-section of W7-X. We have developed models of beam interactions with plasma, and used them to predict measurement sensitivity over a range of plasma densities and a wide variety of W7-X magnetic configurations. Studies of fluctuation induced particle flux will be possible with HIBP measurements of amplitudes, cross-phase and coherence among density fluctuations and potential fluctuations. The system will operate with a 2 MeV beam accelerator and a 340 kV electrostatic energy analyzer. The analyzer and associated power supply and HV cable have necessitated design of a custom resistive protection structure to mitigate damage that could be caused by their stored energy. We will present the results of these efforts as well as an overview of the HIBP design.