Study of hybrid X-pinches with current up to 1.2 MA

Abstract

A hybrid X-pinch configuration consisting of solid conical electrodes connected by a wire was first tested on the 45 ns rise time, 500 kA peak current XP pulsed power generator1. In more recent work the hybrid X-pinch was studied on generators with peak currents from 250 kA to 1.2 MA and current rise time from 45 ns to 170 ns. In all experiments the hybrid pinches have the same 60° conical electrodes made of tungsten (W) with 5% copper (Cu). The wires were loaded trough 1 mm holes in the cones. The wire diameter and the gap between electrodes were varied to fit the pulser peak current and rise time. Mg, Al, Ti, Ni, NiCr, Cu, Mo, Pd, Ag, W and Au wires having lengths ranging from 0.6 to 2.5 mm were tested in the experiments. The wire diameters were varied from 12 to 200 µm for different experimental conditions. The experiments have shown that for each generator, it is possible to find a wire material, diameter and length for which the X-pinches generate an intense single burst of soft x-rays and develop a single hot spot with micron size. Also they generated less hard x-ray intensity than that measured from comparable standard X-pinches. Absence of x-rays with photon energies > 20 keV associated with long-lived electron beams2 is explained by fast closure of the gap between conical electrodes by expanding dense plasma from them. At the same time short-lived electron beam radiation produces bright small-size x-ray source in 6–15 keV spectral band usable for point-projection radiography. Hybrid X-pinches have been used as a source of continuum radiation with a flat spectrum for absorption x-ray spectroscopy of relatively cold plasma of exploded Al wires and wire arrays3. In place of the ∼ 100 µm diameter wires between the conical electrodes we have tested hollow tubes from Al, Ni and polyethylene. Both empty and filled with various materials tubes were tested as a load on COBRA pulser (1.2 MA, 100 ns rise time). This possibility with the hybrid X-pinch configuration greatly expands the range of materials that can be studied under extreme conditions of an X-pinch.