(a) The coiled wires in an array can be aligned so that (b) the trailing mass and imploding sections occur at the same axial position. This type of structure is referred to as an “organised implosion.”
(a) The inverse coiled array configuration used in the experiments on MAGPIE. This places the current return inside the array, changing the direction of the force so that plasma flow is divergent. (b)The COBRA experiments used a convergent (imploding) array configuration. The array illustrated in this figure has 8 coiled wires, although a mixture of straight and coiled wires was used in the experiments.
An interferogram showing the fringe pattern produced by a single wire in a 4-wire inverse array ( Al, ) at 127 ns after current start.
Electron line density maps in the r,z plane produced by interferometry. These show the plasma streams and the distribution of ablated plasma produced from a single coiled wire in a 4-wire inverse array ( Al, ). Two MAGPIE shots were used to obtain this data, with one shot producing the maps at (a) 104 ns and (c) 127 ns, and a second shot producing the maps at (b) 110 ns and (d) 133 ns.
Axial profiles for each of the four maps shown in Figure 4 , showing line-outs of the electron line density at 1.3 mm, 2.0 mm, 3.0 mm, and 4.0 mm from the coil axis.
The variation of the full width half maximum of the ablation streams with distance from the coil axis at a time of 127 ns. The disconnected symbols represent data from three separate ablation streams, while the solid line represents the mean trend.
An XUV image ( ) of the ablated plasma from a single coiled wire in a 4-wire inverse array ( Al, ) at 125 ns after current start.
(a) The radial density profile along the centre of the ablation streams for the maps shown in Fig. 4 . Each of these curves represents the mean of three ablation streams. (b) The radial density profile halfway between two ablation streams (i.e., the centre of the gap between streams). Each of these curves represents the mean of four inter-stream regions shown in Fig. 4 .
(a) Comparison between averaged over the full axial height ofthe data in Fig. 4 and the rocket model, using parameters (Z = 3, ) that have been shown to well represent the ablation from a straight wire. 9 (b) Comparison between the ablation stream profiles from Fig. 8 and the rocket model (Z = 3, ).
(a) Schematic of the axial forces, , on current-carrying plasma close to a coiled wire core in an array, and also on the ablation streams. (b)Gorgon 3D MHD simulation at t = 140 ns showing current, and velocity streamlines in ablated plasma from a coiled wire ( ) in an array. Reprinted with permission from Hall et al., Phys. Rev. Lett. 100, 065003 (2008). Copyright 2008 by the American Physical Society.
(a) An illustration of the ablation flow model proposed in Ref. 1 in which ablated plasma from the azimuthal edges is axially redirected before becoming aligned with the outer edges. This is how the flow would appear in a side view (i.e., in the r,z plane), whilst the view from the rear of the coiled wire looking towards the axis is shown in (b). These diagrams also serve to illustrate the nomenclature used to describe certain points of the helical wire, which are shown as coloured spheres on the wire core. The view of the coiled wire in (b) is exactly the same as shown in the sequence of XUV images in (c), (d), (e), and(f) which shows soft x-ray emission from a coiled wire ( ) with a straight wire visible on the opposite side of the array. These were part of an aluminium array which contained a mix of coiled and straight wires.
(a) The ablation stream model (shown in the side-on view in Fig. 11(a) ) was raytraced using a point source to simulate the view that would be produced by point-projection radiography. (b) A point-project radiograph of a platinum coiled wire and straight wire and the ablated plasma from them. To aid the eye, the ablation streams from one wavelength of the coil are highlighted with dotted lines.
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