Coronal plasma behavior of the Z pinch produced from carbon and cryogenic deuterium fibers

Abstract

A series of fiber pinch experiments has been carried out on the MAGPIE (mega-ampere generator for plasma implosion experiments) generator (1.8 MA, 150 ns) [Mithell et al., Rev. Sci. Instrum. 67, 1533 (1996)] to study the temporal evolution of the coronal plasma. Analysis of schlieren photographs, axial streak images and gated x-ray photographs gives the radial and axial motion of the coronal plasma. The influence of a current pulse (prepulse) of 30 kA applied 200 ns before the main discharge was also studied. Radial expansion velocities of 5.5×106 cm/s for carbon fiber shots without prepulse and 3.6×106 cm/s for carbon fibers with prepulse were measured. Axial wavelengths (λz) of dominant instabilities in the corona were between 0.05 and 0.2 cm corresponding to ka∼10–20. Comparison of the results obtained with carbon fibers with and without current prepulse and cryogenic deuterium fibers are presented.

Carbon fiber Z-pinch driven by microsecond-long capacitive discharge

“…From these values we may conclude that roughly 7 ) one per cent of the total mass of a fiber was ablated at that time. The linear density of the corona N i ≈ 10 17 m −1 was in agreement with the value reached when 7 μm fibers were used during the current prepulse on MAGPIE (35 kA prepulse, 200 ns duration [9]) and on IMP (10 kA, 180 ns period [13]) generators at Imperial College, London. In the latter experiment, the implosion of a low density plasma onto a fiber, the zipper, and the radiation from an m = 0 instability were also observed.…”

“…The subsequent calculation showed that rather than enhancing the stability the core partially masked the evidence of instabilities [5]. Similarly discouraging results were obtained from further and better diagnosed experiments on new generators at NRL [6] and Los Alamos [7] as well as on KALIF at Kernforschungszentrum Karlsruhe [8] and on MAG-PIE at Imperial College in London [9]. The fibers from carbon and deuterated polyethylene were also employed because their discharge behaviour was roughly the same [9,10], and at the same time they were easily available and could be handled much easier than the frozen deuterium ones.…”

“…Similarly discouraging results were obtained from further and better diagnosed experiments on new generators at NRL [6] and Los Alamos [7] as well as on KALIF at Kernforschungszentrum Karlsruhe [8] and on MAG-PIE at Imperial College in London [9]. The fibers from carbon and deuterated polyethylene were also employed because their discharge behaviour was roughly the same [9,10], and at the same time they were easily available and could be handled much easier than the frozen deuterium ones. To our knowledge, the last experiments with deuterium fibers were performed in the late of 1990's and the idea of nuclear fusion and radiative collapse in fiber Z-pinches was abandoned.…”

Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

“…This orientation also suits the geometry of the wire array, as, apart from the "fundamental" modulation of the ablation rate, the dynamics are fairly axially uniform. While end on shadowgraphy and interferometry diagnostics have be fielded in previous experiments, 3,6,13,14 the work presented in this paper represents a significant improvement, both in terms of the apparatus used and the analysis techniques employed.…”

“…Previous work has demonstrated that the ablation rate along the length of the wires is modulated at a characteristic "fundamental" wavelength, 3,13 driven by a modified form of the m ¼ 0 plasma instability 20 (for aluminium this wavelength is k f ðAlÞ $ 0.5 mm 7 ). Apart from this modulation, the overall dynamics of cylindrical wire arrays appear to be fairly uniform along their length.…”