Study of the fine structure of the plasma current sheath and magnetic fields in the axial region of the PF-1000 facility

Abstract

Results of measurements of magnetic fields in the plasma pinching region during the compression of the deuterium plasma current sheath (PCS) at the PF-1000 plasma focus facility are presented. The fine structure of the PCS (shock wave-magnetic piston) and its variations in the course of plasma compression toward the facility axis are studied using magnetic probes and laser interferometry. The radial distributions of the plasma density and current in the PCS are compared. It is shown that, in the shock wave region, the electron density of the compressed plasma is on the order of ∼1018 cm−3, whereas the PCS current is almost entirely concentrated in the magnetic piston region—a plasma layer with an electron density of less than 1015 cm−3. Efficient transportation of the current by the PCS into the axial region of the facility in discharges with a high neutron yield (Yn > 1011 neutrons/shot) is detected. It is shown that the total neutron yield is well described by the dependence Yn ≈ (1.5–3) × 1010Ip4, where Ip is the pinch current (in MA) flowing within the region r ≤ 13 mm.