Growth and saturation of the axial instability in low wire number wire array Z pinches

Abstract

The growth of the axial instability in low wire number wire array Z pinches using a 100 ns rise time, 1 MA pulsed power accelerator is examined. The axial instability manifests itself as a quasiperiodic variation of the radius of the coronal plasma along each wire and a consequent modulation of the rate of ablation of material from the dense wire core. The dominant wavelength of the modulation becomes constant late in time. In this work laser shadowgraphy is used to measure the growth of the wavelength and amplitude of the instability as well as the size of the coronal plasma in aluminum wire arrays from the time of plasma formation to the time the wavelength seen late in time is reached. Using magnetic probes, the distribution of current and magnetic topology are also investigated. It is found that a distinct change in magnetic field topology associated with the onset of advection of current to the array axis by the streaming wire-ablation plasma appears to be responsible for ending the growth of the axial instability and initiating the quasisteady state ablation phase of the wire array Z pinch.

Use of vacuum arc plasma guns for a metal puff Z-pinch system

“…At the same time, as validly mentioned by the authors of Ref. 6, the small university setups, allowing low-cost experimentation, are well suited for testing both new diagnostics [6][7][8][9] and new schemes for realization of proper initial conditions in imploding plasma shells in Zpinch experiments.…”

“…Hence, the wire array should consist of 5-15 wires spaced some parts of a centimeter or even several centimeters apart. When the distance between the wires is large, severe ablation occurs at the wire surface, 7,8 which reduces both the implosion velocity and the radiation power of the Z-pinch.…”

“…[6][7][8][9] The Z-pinch experiments carried out on terawatt setups are aimed at optimizing the conditions for soft X-ray production [1][2][3][4][5] or at realizing controlled thermonuclear fusion. 3,4 These experiments are very time-consuming and expensive.…”

Ablation dynamics in wire array Z-pinches under modifications on global magnetic field topology

“…In particular, once the ablation streams from the wires have developed, they present axial modulations with a typical wavelength dependent on the wire material (k $ 0.5 mm for Al, k $ 0.25 mm for W), which is a consequence of the global field topology that swept the coronal plasma accumulated in the vicinity of the wires away from them. 11,12 Furthermore, it has been found that these streams can be narrowed by the field penetration within the array and its curvature close to each wire. 13 The ablation dynamics in wire arrays is not only important because of their influence on the implosion, as it determinates the x-ray emission from these configurations 1,6,14 but also is interesting object to study collisionality processes in dense magnetized supersonic plasma flows.…”

Role of electromagnetic wave in mode selection of magnetically driven instabilities

“…In wire array implosions axial nonuniformity of wire ablation results in plasmas colliding on the axis at a time that depends on axial position and a consequence decrease in implosion symmetry [5]. In the case of solid liner implosions, the magneto-RayleighTaylor (MRT) instability results in breakup of liner which has been taken as the greatest threat to MagLIF.…”