Method of measuring SPARC fusion power using the poloidal neutron camera and magnetic proton recoil neutron spectrometer*

Fusion power is a key figure of merit by which fusion experiments are judged. Accurate measurement of the fusion power is therefore a critical requirement for SPARC, motivating the development of multiple sets of diagnostics capable of independent assessment of fusion power. This work describes a method of determining fusion power using the poloidal neutron camera and the magnetic proton recoil (MPR) neutron spectrometer. By making spatially resolved measurements of the Deuterium-Tritium (DT) fusion reactivity, the neutron camera provides the relative shape of the reactivity profile while the ab initio calibrated MPR spectrometer provides the absolute calibration. The total DT fusion rate is then determined by integrating the measured profile over the plasma volume. Unlike other methods of fusion power measurement, this method does not rely on an in situ neutron source calibration because the well collimated lines of sight and energy-resolving capabilities of the detectors allow the neutrons emitted from within their fields of view of the plasma to be discriminated from neutrons which have scattered off surrounding materials. In addition, the collocation of the neutron camera and spectrometer reduces model uncertainty in relating their measurements. Preliminary analysis suggests that the uncertainty associated with this method of determining the DT fusion rate is less than 10% with 250 ms time resolution for fusion power greater than 1 MW.