Influence of stub anode on plasma motion and neutron yield in an 18-kJ plasma focus

Influences of stub anode on current sheath (CS) implosion and pinching as well as on neutron yield have been investigated on the DPF-40 Mather-type plasma focus device (20 kV, 18 kJ). The results show that the stub stabilizes the imploding CS and localizes the plasma pinch, which can be attributed to the azimuthal magnetic field introduced in front of the CS by an anode end discharge induced by the “needle point”-like stub. A centered single stub deteriorates the pinch dynamics and causes the neutron yield to be low and to have large shot-to-shot deviation. Three cases of effects on the plasma motion by the single stub can be distinguished according to the relative height of the stub (Is) to the axial height of the CS (Zcs): Is > Zcs, Is ∼ Zcs and Is < Zcs. The higher the stub the worse the pinch and neutron yield. When Is ≥. Zcs, the CS front moves along the stub and greatly changes the configuration and status of motion of the CS. The CS and pinch can also be stabilized and localized by a non-centered multi-stub anode. It is advantageous to the pinch dynamics and produces a higher mean neutron yield with less deviation (Yn=(2.9 ± 0.5) × 10⁸ per shot, Δ Yn /Yn= ± 17%).