Development of a novel ion energy analyzer for electric potential diagnosis of fusion plasmas*

Direct measurement of potential in magnetically confined plasmas can help validate theoretical models and advance understanding of electric fields and shear on transport. A beam probe can obtain spatially localized measurements of equilibrium electric potential and ion-scale fluctuations of potential in the interior of hot plasmas. It precisely measures the difference between the energies of injected beam particles and detected secondaries originating from small regions of the plasma. Factors often limiting deployment of beam probe diagnostics are their size and cost. To permit diagnostic deployment at a wider range of facilities, we are developing a smaller analyzer that is more economical, yet also maintains necessary energy measurement precision. To achieve this, we are merging a cylindrical ion energy analyzer with a beam angle detector. This will enable precise inference of particle energy (and thus plasma potential) by combining particle entrance angle data with measurements of particle deflection through the cylindrical analyzer and onto detectors. Simulations guiding the design and predicting the performance of this analyzer will be presented. Once fabricated, we will calibrate the analyzer on a beamline test stand then deploy it on the Madison Symmetric Torus at WIPPL.