Measurements of steady neutron production at the Centrifugal Mirror Fusion Experiment

The latest neutron production measurements from deuterium plasmas sustained in the Centrifugal Mirror Fusion Experiment (CMFX) are presented. Voltages of up to 85 kV have sustained for hundreds of milliseconds at CMFX using a DC high voltage power supply, with lower voltages sustained up to 10 seconds, with the limit of sustainment time only constrained by heating of electrodes and insulators (plans for active cooling of components are discussed). The applied voltages results in supersonic E x B rotation, with velocities in the azimuthal direction exceeding 1,700 km/s in deuterium plasmas. These high velocities also generate flow shear and heating, resulting in total sustained neutron productions estimated at 10⁷ neutrons per second. These neutron rates indicate plasma temperatures must be around 1 keV for plasma densities of 2 – 4 x 10¹⁸ m^-3. Neutral gas can be added in bursts during plasma discharges, leading to an increase in density and neutron production that slowly decays with confinement times of tens of milliseconds. Experiments are underway with two ³He detectors to time-resolve the neutron production with respect to applied voltage, and to spatially resolve the plasma region producing the neutrons. Other techniques to detect neutrons, such as CR-39 plastic coupons, and activation of materials, are being used to gather enough spatial resolution for tomographic reconstruction of the plasma volume. B-dot probes, Thomson scattering, ion Doppler spectroscopy, interferometry, and soft x-ray diodes are also being developed to demonstrate the close adherence of experimental results to theoretical models.