Relationship Between Neutron Yield and Macroscale Pinch Dynamics of a 1.4-kJ Plasma Focus Over Hundreds of Pulses

The plasma focus (PF) is a potent neutron source, but the reproducibility of the source is seldom studied over more than tens of shots. The data presented herein examine the PF at the same pressure, charge voltage, and electrode geometry over 930 shots. The neutron yield at 230 kA was found to be 5.6 × 10⁷ neutrons/pulse with a standard deviation of 55%. The highest yield shots exceed 10⁸ neutrons/pulse. Using terminal measurements of voltage and current, the time-varying inductance and the pinch voltage were derived. A linear relationship was found between the minimum in the time derivative of the current (dI/dt) and the pinch voltage. Increasing pinch voltage correlated with increasing neutron yield at the same peak current. Therefore, it is desirable to increase the (absolute) minimum in dI/dt and, thus, the current “bite” to increase the neutron yield. The large deviation in the neutron yield cannot be explained using terminal measurements alone, so time and spatially resolved diagnostics are needed to better understand if measurable macroscale properties such as pinch geometry provide insight into the neutron yield standard deviation.