Influence of Insulator Length on the Downstream Electron Temperature and Density in the Coaxial Plasma Focus Device

We have generated the Ar plasma in the diode chamber based on the established coaxial electrode type and investigated the emitted visible light for emission spectroscopy. The optical emission spectrum data have been obtained for the focused plasma in the cylindrical diode chamber under the input voltage of 4.5 kV and pressure of 40 mtorr. We observed the nine emission lines of Ar II: 407.3, 410.6, 422.4, 426.8, 427.9, 435.0, 438.1, 444.5, and 488.0 nm. The downstream electron temperature and density have been measured by the Boltzmann plot and Stark broadening, respectively, from the assumption of local thermodynamic equilibrium. The length of the acrylic insulator has been changed to 30, 40, and 45 mm, respectively, which is covered on the inner cathode surface, to investigate the influence of insulator length on the downstream electron temperature and density in this experiment. Our results show that the downstream electron temperature and density of focused plasma are 2.5 eV and 1.6times10¹⁶ cm^-3, respectively, for the coaxial plasma focus with cylindrical electrodes at the insulator length of 40 mm.