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Staged pinch implosions provide a means to couple energy to a small-diameter fibre on an extremely fast time scale, circumventing the limitations of conventional pinches. In this scheme the generator current initially traverses an intermediate hollow plasma shell, which compresses onto the fibre placed coaxially and transfers the current to the fibre with a significantly reduced risetime. The results are impressive, since the delivered peak power is increased by several orders of magnitude, the coupling efficiency improves, and the most dangerous plasma instabilities that commonly plague high-density/high-temperature pinches are eliminated. This technique can be fielded on both fast and slow generators (i.e. tens of nanoseconds to microseconds), making it feasible to extend the concept to a wide range of presently assembled systems. Staging may therefore present a dramatically new means of pulsed-energy conversion, which could find many applications. In addressing the requirements for thermonuclear fusion in a staged Z pinch, our preliminary calculations based on zero-D models suggest the potential for a significant thermonuclear burn with generator currents of the order of a few megaamperes and one microsecond risetime. Studies are actively underway at various places around the world (England, France, Germany and Russia) as well as in the USA (UCI/UCR) to investigate different aspects of staged pinching and its applications, particularly those leading to controlled thermonuclear fusion.
A critical limitation of magnetically imploded systems such as magnetized liner inertial fusion (MagLIF) [Slutz et al., Phys. Plasmas 17, 056303 (2010)] is the magneto-Rayleigh-Taylor (MRT) instability which primarily disrupts the outer surface of the liner. MagLIF-relevant experiments have showed large amplitude multi-mode MRT instability growth growing from surface roughness [McBride et al., Phys. Rev. Lett. 109, 135004 (2012)], which is only reproduced by 3D simulations using our MHD code Gorgon when an artificially azimuthally correlated initialisation is added. We have shown that the missing azimuthal correlation could be provided by a combination of the electro-thermal instability (ETI) and an "electro-choric" instability (ECI); describing, respectively, the tendency of current to correlate azimuthally early in time due to temperature dependent Ohmic heating; and an amplification of the ETI driven by density dependent resistivity around vapourisa-tion. We developed and implemented a material strength model in Gorgon to improve simulation of the solid phase of liner implosions which, when applied to simulations exhibiting the ETI and ECI, gave a significant increase in wavelength and amplitude. Full circumference simulations of the MRT instability provided a significant improvement on previous randomly initialised results and approached agreement with experiment. V C 2015 AIP Publishing LLC.
A staged Z pinch is considered in which an annular plasma shell made of a high Z material like Kr implodes onto a coaxial plasma target made of a low Z material like deuterium or a deuterium–tritium mixture. The target plasma could be made either by exploding a cryogenically extruded fiber or by filling the annular shell with a gas puff or a plasma puff. Modeling is performed with a two-dimensional (2D) radiation-MHD (magnetohydrodynamic) code. A parameter study is made to determine the sensitivity of this configuration to initial conditions of the shell and the target plasmas. An axial magnetic field is essential for a stable implosion and efficient energy coupling to the final load. Using a 50–50 mixture of deuterium–tritium as a target plasma, the fusion energy gain is optimized by adjusting the initial parameters. The calculations are based on the parameters of the University of California Irvine Z-pinch facility which has a maximum energy storage of 50 kJ.
A Staged Z-pinch (H.U. Rahman, F.J. Wessel, N. Rostoker, Phys. Rev. Lett. 74:714, 1995), configured for a 100 ns, 2 MJ implosion accelerator, is studied using the 2-1/2 D, radiation-MHD code, MACH2. The Z-pinch is configured as a cylindrical, high-atomic number plasma shell that implodes radially onto a co-axial, plasma target, for example: Xenon onto a 50:50 mixture of Deuterium-Tritium. During implosion a shock develops in the plasma liner, producing a conduction channel at the Xe/DT interface as the mass Xe accumulates, and preheating the DT target. During subsequent acceleration and compression the Xe/DT interface remains stable, even as the outer surface of the Xe shell develops RT instabilities. At peak implosion the simulated fusion-energy yield is 7.6 MJ, producing an energy gain of 3.8. Keywords Magneto-inertial fusionThe Z pinch has been studied as a means to attain highenergy-density plasma compressions for many decades (Teller 1981). During implosion the Z-pinch becomes Rayleigh-Taylor unstable; as a light fluid (pinch-magnetic field) pushes against a heavy fluid (plasma). In the linearregime of analytic treatment, plasma perturbations grow as H.U. Rahman · N. Rostoker · F.J. Wessel ( ) Physics and Astronomy, Univ. of California, Irvine, CA 92697, USA e-mail: frank.wessel@uci.edu P. Ney Dept. Physics, Mount San Jacinto College, Menifee, CA 92584, USA (Chandrasekar 1981),where ξ 0 is the initial perturbation, γ = √ gk is the growth rate, g is the acceleration, k is the wavenumber, and t is the time. A rough approximation for the distance over which the plasma is accelerated is the initial radius, and using, R 0 = gt 2 /2, ξ is re-written as,
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