AbstractThe characteristics of a low energy plasma focus of copper electrodes operated by a single 32 μF, 15 kV (3.6 kJ) capacitor with an insulator sleeve contamination are studied. When the plasma focus is operated, the insulator sleeve is contaminated due to the deposition of copper evaporated from the electrodes. A slight contamination improves the system performance. When the cumulative discharge energy over successive shots across the insulator sleeve exceeds ∼ 1 MJ, the copper deposition on the sleeve surface makes it rough with a grain-type structure, with as result that the system becomes less reproducible and shot-to-shot variations in neutron yield are pronounced. In addition, a high voltage probe records multiple foci formation, giving rise to multiple neutron pulses, multiple X-ray pulses as well as multiple ion beams. When the cumulative discharge energy approaches 1.6 MJ, the neutron yield starts deteriorating, and the resistor divider signal begins to indicate less compression. It is suggested that the neutron yield degradation occurs due to copper coating with grain structure on the sleeve surface, which decreases the resistance of the sleeve surface and may therefore increase the current partition and eventually lower the snowplow efficiency. The situation may improve if low-sputtering-rate conductors are employed for the electrodes of the device or the truncated end of the anode is lined with low sputtering rate material like molybdenum.