Study of stability in a liner-on-target gas puff Z-pinch as a function of pre-embedded axial magnetic field

Conti, F.; Aybar, Nicholas; Narkis, J.; Valenzuela, Jorge; Rahman, H. U.; Ruskov, E.; Dutra, Eric; Haque, Showera; Covington, A. M.; Beg, F. N.

doi:10.1063/1.5131170

Cited by 17 publications

(5 citation statements)

References 40 publications

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“…In the first method, the stabilization mechanism works as follows: the magnetic shear between the compressed magnetic field B z inside a Z-pinch and the compressive azimuthal magnetic field B θ outside it enhances the stability of the imploding plasma shell and suppresses the growth of MRT instabilities [2,[16][17][18]. The implosion of Z-pinches can be stabilized by comparatively low B z fields [17].…”

Section: Introductionmentioning

confidence: 99%

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

Cherdizov¹,

Baksht²,

Kokshenev³

et al. 2021

Plasma Phys. Control. Fusion

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To study the effect of the radial density profile of the material of a metal-plasma Z-pinch load on the development of magneto-Rayleigh-Taylor (MRT) instabilities, experiments have been performed at the Institute of High Current Electronics with the GIT-12 generator produced microsecond rise time megaampere currents. The load was an aluminum plasma jet with an outer plasma shell. This configuration provides the formation of a uniform current sheath in a Z-pinch load upon application of a high voltage pulse. It was successfully used in experiments with hybrid deuterium gas-puffs [Klir et al. 2020 New J. Phys. 22 103036]. The initial density profiles of the Z-pinch loads were estimated from the pinch current and voltage waveforms using the zero-dimensional "snowplow" model, and they were verified by simulating the expansion of the plasma jet formed by a vacuum arc using a two-dimensional quasi-neutral hybrid model [Shmelev et al. 2020 Phys. Plasmas 27 092708]. Two Z-pinch load configurations were used in the experiments. The first configuration provided tailored load density profiles, which could be described as ρ(r) ≈ 1/r^s for s > 2. In this case, MRT instabilities were suppressed and thus a K-shell radiation yield of 11 kJ/cm and a peak power of 0.67 TW/cm could be attained at a current of about 3 MA. For the second configuration, the radial density profiles were intentionally changed using a reflector. This led to the appearance of a notch in the density profiles at radii of 1–3 cm from the pinch axis and to magnetohydrodynamic instabilities at the final implosion stage. As a result, the K-shell radiation yield more than halved and the power decreased to 0.15 TW/cm at a current of about 3.5 MA.

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Section: Introductionmentioning

confidence: 99%

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

Cherdizov¹,

Baksht²,

Kokshenev³

et al. 2021

Plasma Phys. Control. Fusion

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“…The average implosion velocity is 100 km=s, which is a factor of 3 lower than measured in previous experiments conducted on a 1 MA, 100 ns driver with a similar setup [64]. However, a large zippering effect and MRT instability were still observed in the plasma column, despite the slower implosion.…”

Section: B Gas Puff Z Pinchmentioning

confidence: 49%

MA-class linear transformer driver for Z -pinch research

Conti

Valenzuela

Fadeev

et al. 2020

Phys. Rev. Accel. Beams

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A linear transformer driver (LTD) generator capable of delivering up to 0.9 MA current pulses with 160 ns rise time has been assembled and commissioned at University of California San Diego. The machine is an upgrade of the LTD-III pulser from Sandia National Laboratories, consisting of 40 capacitors and 20 spark gap switches, arranged in a 20-brick configuration. The driver was modified with the addition of a new trigger system, active premagnetization of the inductive cores, a vacuum chamber with multiple diagnostic ports, and a vacuum power feed to couple the driver to plasma loads. The new machine is called compact experimental system for Z-pinch and ablation research (CESZAR). The driver has a maximum bipolar charge voltage of AE100 kV, but for reliability and testing, and to reduce the risk of damage to components, the machine was operated at AE60 kV, producing 550 kA peak currents with a rise time of 170 ns on a 3.5 nH short circuit. While the peak current is scaled down due to the reduced charge voltage, the pulse shape and circuit parameters are close to the results of the cavity and power feed models but suggest a slightly higher inductance than predicted. The machine was then used to drive wire array Z-pinch and gas puff Z-pinch experiments as initial dynamic plasma loads. The evolution of the wire array Z pinch is consistent with the general knowledge of this kind of experiment, featuring wire ablation and stagnation of the precursor plasma on axis. The gas puff Z pinches were configured as a single, hollow argon gas shell, in preparation for more structured gas puff targets such as multispecies, multishell implosions. The implosion dynamics agree generally with 1D magnetohydrodynamics simulation results, but large zippering and magneto-Rayleigh-Taylor instabilities are observed. The CESZAR load region was designed to accommodate many load types to be driven by the machine, which makes it a versatile platform for studying Z-pinch plasmas. The completion of the CESZAR driver allows plasma experiments on energy coupling from LTD machines to plasma loads, instability mitigation techniques and magnetic field distributions in Z pinches, and interface dynamics in multispecies implosions.

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“…In many cases, an external axial magnetic field is applied to stabilize the implosion or provide the 'magneto-thermo-insulation' (Lindemuth & Kirkpatrick 1983) of the stagnated plasma, which is the critical issue for all approaches to magnetized target fusion and magneto-inertial fusion (Turchi 2008;Garanin 2013;Wurden et al 2016;Lindemuth 2017), including the MagLIF. The axial magnetic field, in turn, can affect the implosion dynamics in various ways, not all of which are fully understood; see Felber et al (1988), Shishlov et al (2006), Rousskikh et al (2017), Mikitchuk et al (2019), Conti et al (2020), Seyler (2020) and references therein. Recent experiments with gas-puff Z-pinch implosions in an external magnetic field (Cvejić et al 2022) demonstrated a self-generated rotation of the imploding axisymmetric plasma.…”

Section: Introductionmentioning

confidence: 99%

Stable and unstable supersonic stagnation of an axisymmetric rotating magnetized plasma

et al. 2022

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The Naval Research Laboratory ‘Mag Noh problem’, described in this paper, is a self-similar magnetized implosion flow, which contains a fast magnetohydrodynamic (MHD) outward propagating shock of constant velocity. We generalize the classic Noh (OSTI Tech. Rep. 577058, 1983) problem to include azimuthal and axial magnetic fields as well as rotation. Our family of ideal MHD solutions is five parametric, each solution having its own self-similarity index, gas gamma, magnetization, the ratio of axial to the azimuthal field and rotation. While the classic Noh problem must have a supersonic implosion velocity to create a shock, our solutions have an interesting three-parametric special case with zero initial velocity in which magnetic tension, instead of implosion flow, creates the shock at $t=0+$ . Our self-similar solutions are indeed realized when we solve the initial value MHD problem with the finite volume MHD code Athena. We numerically investigated the stability of these solutions and found both stable and unstable regions in parameter space. Stable solutions can be used to test the accuracy of numerical codes. Unstable solutions have also been widely used to test how codes reproduce linear growth, transition to turbulence and the practically important effects of mixing. Now we offer a family of unstable solutions featuring all three elements relevant to magnetically driven implosions: convergent flow, magnetic field and a shock wave.

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Study of stability in a liner-on-target gas puff Z-pinch as a function of pre-embedded axial magnetic field

Cited by 17 publications

References 40 publications

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

MA-class linear transformer driver for Z -pinch research

Stable and unstable supersonic stagnation of an axisymmetric rotating magnetized plasma

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