Anisotropic and asymmetric fast ion distribution generated by magnetic reconnection in MST plasmas

Magnetic reconnection drives ion energization in both astrophysical and laboratory plasmas. In the reversed-field pinch (RFP), reconnecting plasma with a turbulent spectrum creates an ion distribution with distinct asymmetry and anisotropy. Both the energization mechanisms and the diffusion of the accelerated particles are crucial in creating and sustaining the distribution, which produces fusion neutron flux several orders higher than a typical thermal distribution. The resulting anisotropic fast ion distribution has been measured in MST using a neutral particle analyzer and neutron detectors. A collimated neutron diagnostic is also being developed for localized spatial measurements of neutron flux. Transport modeling can adequately explain the measurements, with the caveat that the perpendicular heating mechanism of thermal ions isn’t yet completely understood. A full orbit particle tracer is quantifies the asymmetric diffusion in velocity-space, compared with neutron decay rate data using neutral beam blips. Fokker-Planck calculations mimic the time evolution of fusion neutrons when taking into account asymmetric drive and diffusion, compared with NPA data along three lines of sight. Work supported by US DOE.