Effects of the Cathode Grid Wires on Fusion Proton Measurements in Inertial-Electrostatic Confinement Devices

Gridded inertial-electrostatic confinement (IEC) devices interest fusion researchers owing to their ability to burn advanced fusion fuels and have many near-term applications. In these devices, a high voltage (10-180 kV) accelerates ions radially between nearly transparent electrodes in spherical or cylindrical geometry. In this paper, we report experiments that study fusion reactions within the microchannels formed between the wires of the nearly transparent IEC cathode grid. Fusion proton counts were measured while sweeping the microchannels across a proton detector by rotating the central cathode grid with respect to the detector. The observed proton counts increased or decreased in correspondence with the grid wire orientation with respect to the proton detector. The fusion reactions were thus inferred to be nonuniform around the central grid and primarily occurring in channels formed by the grid wire gaps. We interpret this effect as an indication that most ions and charge-exchanged neutrals traverse radially along these microchannels. The grid wires will also shadow fusion reactions taking place at radii smaller than the cathode radius. Both the microchannels and the grid-wire shadowing causes the proton counts to vary, in measurements presented herein, by as much as 45%. We explore whether these effects could have played a role in previous research that reported potential-well structures.