Study of implosions in star-like wire arrays with “gates” on the inner cylinder

Summary form only given. Star-like wire arrays with two closely located wires ("gates") on the inner cylinder were studied on the 1-MA Zebra generator. The hydrodynamic mode of collision is typical for regular star-like wire arrays and it was observed with shadowgraphy and optical streak cameras. In this mode, star-like wire arrays generate a short 8-12 ns X-ray pulse. The star-like wire arrays were modified to reach a transparent mode typical for multiwire nested arrays. The wire on the inner cylinder of the star load was changed for two wires located symmetrically on both sides of the arms of the star. Shadowgraphy shows that the imploding plasma does not pass through gates 0.3 to 1.2 mm wide; the plasma is trapped between the gates. Plasma columns are formed at the initial position of the gates, then finally implode to the center of the array. Gates in double-cylinder wire arrays help to make the imploding plasma more inhomogeneous and increase the radiated power. Gated star arrays demonstrate similar dynamics of X-ray generation compared to regular star arrays. Gated linear wire array configurations were also tested. The observed plasma dynamics will be compared with the calculated magnetic fields in wire arrays. Long wires were applied at the gates to increase their inductance and provide a transparency for the imploding plasma. The wires of the gates were made out of Al or high-Z elements. Shadowgraphy at the wavelength of 266 nm showed that plasma moves through the gate wires. Double implosions were observed in star arrays when gates were made out of high-Z elements. This implosion generates a double-peak keV X-ray pulse and wide soft X-ray pulse with the duration of 25-35 ns. The Al gates were partly transparent for the imploding plasma. Al star arrays with Al gates generated a single X-ray pulse with the duration of 12-15 ns. The implosion of the external wires can be used for the formation of a precursor discharge in the wire array. Transparent and hydrod- namic modes can be studied with star-like wire arrays.