Unconventional plasma focus devices

The Plasma Focus (PF) characteristics have been investigated in the Two-Guns configuration (TWIN) with a 10-kJ class device. Electrodes with two different heads shapes, hollow (GYN) or hemispherical (PHAL), have been tested and the results show that the neutron yield is greater in the GYN configuration. In simple Two-Guns configuration, with the two anodes facing frontally in the vacuum vessel, the neutron yield corresponds to the sum of two independent PFs yields, as long as the inter-anode distance is larger than twice their radius. Shorter distances reduce progressively the neutron yield, but there is evidence that two foci are still formed. When the two anodes are connected by a metallic rod (COLL configuration) neutron production is still present, although reduced. For this configuration, experimental data are reported in function of the rod length and radius, capacitor bank energy, and deuterium pressure. The results agree with a simple theory based on the ballistic collision of two plasma sheaths coming from the two facing parts of the apparatus. Sheaths velocities of about 10⁸ cm/s and impact energies of about 35 keV have been inferred. The scaling of the COLL apparatus is investigated.