Differences in shots with high and low neutron yield production in mega-ampere plasma focus discharges

The paper presents a comparison of shots with high and low neutron yield at deuterium filling. Shots with high neutron yield are characterized by a higher energy produced hard x rays and neutrons, a larger volume of plasmoid-like compact structure, and lower plasma density in the pinched column. The discrepancy was interpreted by different magnetic energies stored in the pinched column. The model of distribution of magnetic energy in a plasmoid assumes the existence of a poloidal component of magnetic field in the plasma, the formation of compact structures with closed poloidal and toroidal current components, filamentary distribution of the current, and development of MHD instabilities along the filaments. The model meets the characteristics of observed sources of fast deuterons, such as submillimeter dimensions, various directions of path with narrow directivity, and radial and azimuthal configuration of spots. The presented mechanism of acceleration of fast deuterons is based on the model of magnetic reconnection, in which part of the disappearing magnetic field induces a strong electric field sufficient for obtaining hundreds of keV energy.