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Wire array Z-pinch experiments on the MAGPIE generator , simulations and theory
| Content Provider | Semantic Scholar |
|---|---|
| Author | Haines, Malcolm G. Lebedev, Sergey V. Chittenden, Jeremy P. Aliaga-Rossel, Raúl Bland, Simon Nicholas Dangor, A. E. |
| Abstract | Fast z-pinch implosions are an effective way of converting stored electrical energy into xrays. Among other applications [1], pinch x-ray sources are used to energise hohlraums to blackbody temperatures of ~ 150 eV[2] for experiments relevant to the indirect drive ICF program and other radiation-hydrodynamic studies. Power levels of up to ~ 200 TW[3] have been obtained by the use of cylindrical arrays of large numbers (~240) of thin metallic wires as a z-pinch load. There is a general understanding that the high degree of symmetry of the load in large wire number shots is a key factor in attaining high Xray power [4]. In this paper we present measurements of the dynamics of plasma formation in wire-array z-pinches. The experiments were carried out on the MAGPIE (Mega Ampere Generator for Plasma Implosion Experiments) generator [5] with current rising up to 1 or 1.4 MA in 240 ns (10% to 90% rise-time is 150 ns). Figure 1 shows a schematic of the wire array load used in this experiment. The 1.6 cm diameter 2.3 cm long annular wire array is mounted between the live cathode and the anode plate. Eight current-return posts are situated on a diameter of 15 cm. The design allows both end-on and side-on diagnosis of the whole array. Experiments were performed with arrays of 8, 16, 32 and 64 aluminium wires of 15 μm diameter. A frequency doubled Nd-YAG laser (532 nm) with SBS pulse compression (0.4 ns) was used for optical probing and CCD (charge coupled device) cameras were used as the recording media. Figure 2 shows a typical side-on schlieren photograph of the array with 8 wires at 148ns after the current start. It is seen that the coronal plasma expands with the development of an m=0 like instability with axial wavelength of ~0.5 mm. These instabilities are similar to those observed in single wire z-pinches [6,7,8], but the global magnetic field modifies the instability pattern, which is no longer symmetric around each wire axis. Comparison of these instabilities in different wires shows that they are not correlated during the initial stage of the discharge. This supports assumptions used in the heuristic model of the wire array z-pinch [9] to determine subsequent average amplitude of seed perturbations at shell formation. From the schlieren photographs, taken at different times after the current start, it is possible to determine the dynamics of the coronal plasma expansion from the wires in both the radial and azimuthal directions. The increasing size of the plasma around wires at the edge of the array provides measurements of velocities of the inward (to the array axis) and outward radial motion of the coronal plasma (Fig.3). Fig. 1. The schematic of the wire array design to allow measurements of the azimuthal structure of the plasma by end-on interferometer. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://epsppd.epfl.ch/Maas/web/pdf/p1033.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
