GDT Device. Recent Results and Future Plans for GDT Upgrade

GDT experiments of significance to a GDT-based neutron source development are reported in the areas of generation of axially peaked neutron flux profile, stable confinement with on-axis plasma beta ~ 40%, and radial electric field control. Skew injection of 4MW 15-17keV deuterium neutral beams into central cell resulted in generation of strongly peaked axial profile of neutron flux density. This can be described by a model of fast ion relaxation, which involves only classical mechanisms of electron drag and binary ion-ion collisions. Experiments with the radial limiter biasing show that the plasma density profile and radial losses respond to the electric filed profile. An increase of plasma energy was achieved with increased magnetic field in the central cell and optimized radial profile of electric field in the plasma. In these regimes of improved target plasma confinement, the on-axis plasma beta near the turning points of fast deuterons exceeded, as above mentioned, ~40%. The plans for future upgrade of the GDT device are discussed. It suggests considerable increase of NB injected power (up to 10MW) and extension of the pulse duration from 1ms to 3-5ms. After the upgrade, a significant increase of the electron temperature to 250-300eV could be obtained. Properties of the plasma with the parameters approaching those in the full-scale neutron source are planned to study in experiments with NB injection into additional cell near the end mirror.