Influence of gas conditions on parameters of plasma jets generated in the PF-1000U plasma-focus facility

Several series of high-current discharges were carried out within the PF-1000U facility at various gas conditions. The initial filling pressures were p0 = 1.2 hPa D2, 1.06 hPa D2 + 10% He, or 0.53 hPa D2 + 25% Ne. The discharges were performed with or without an additional gas puffing. In shots with the puffing, 1 cm3 of gas (or mixture), compressed to the pressure of (0.13–0.20) MPa, was injected 1.5 ms before the discharge initiation. Pure D2, He, Ne, or a mixture of 50% He + 50% Ne was used for puffing. The optical spectroscopic measurements were performed at a distance of 16 or 27 cm from the electrode outlets. Almost all discharges produced a dense plasma-focus (of about 10 cm in length) and a long plasma jet, which was observed for several μs. The ambient plasma density at the investigated gas-conditions was about 1016 cm−3, but an admixture of 10% He or 25% Ne (added to the D2-filling) induced an increase in this density by factor 1.8–2.5. In all the cases, the plasma jet density was above 10-times higher than that of ambient plasma. At the He- or Ne-puffing, this density reached (3.5–6) × 1017 cm−3. Electron temperatures in the plasma jet changed from about 5.0 to about 3 eV in 5–7 μs.