Ion-Kinetic-Energy Measurements and Energy Balance in a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math>-Pinch Plasma at Stagnation

Kroupp, E.; Osin, D.; Starobinets, A.; Fisher, V.; Bernshtam, V.; Maron, Y.; Uschmann, I.; Förster, E.; Fisher, A.; Deeney, C.

doi:10.1103/physrevlett.98.115001

Cited by 40 publications

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“…This behavior occurs in plasma, but is not predicted by studies of neutral gas compression [7][8][9][10][11][12][13]. In fact, it was observations of the dominant effect of the TKE in Zpinches, both in pressure balance [4] and in radiation balance [2,4], that stimulated the present study.Compression is rapid if the rate of compression is fast compared to the turbulent timescale τ = k/ with k the TKE and the viscous dissipation rate. In the initially rapid plasma compressions here, the viscous dissipation eventually grows such that the turbulent timescale τ shortens, and the plasma TKE suddenly dissipates.…”

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confidence: 68%

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confidence: 68%

“…The plasma motion in these compressions can be turbulent, whether magnetically driven [1][2][3][4] or laser driven [5,6]. However, rapid compression of this turbulent plasma, where the viscosity is highly sensitive to temperature, is demonstrated here to exhibit unusual behavior, where the turbulent kinetic energy (TKE) abruptly switches from growing to rapidly dissipating.…”

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confidence: 82%

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Sudden Viscous Dissipation of Compressing Turbulence

Davidovits

Fisch

2016

Phys. Rev. Lett.

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Compression of turbulent plasma can amplify the turbulent kinetic energy, if the compression is fast compared to the viscous dissipation time of the turbulent eddies. A sudden viscous dissipation mechanism is demonstrated, whereby this amplified turbulent kinetic energy is rapidly converted into thermal energy, suggesting a new paradigm for fast ignition inertial fusion.Introduction.-Unprecedented densities and temperatures are now reached by compressing plasma using lasers or magnetic fields, with the objective of reaching nuclear fusion, prodigious x-ray production, or new regimes of materials. The plasma motion in these compressions can be turbulent, whether magnetically driven [1][2][3][4] or laser driven [5,6]. However, rapid compression of this turbulent plasma, where the viscosity is highly sensitive to temperature, is demonstrated here to exhibit unusual behavior, where the turbulent kinetic energy (TKE) abruptly switches from growing to rapidly dissipating. This behavior occurs in plasma, but is not predicted by studies of neutral gas compression [7][8][9][10][11][12][13]. In fact, it was observations of the dominant effect of the TKE in Zpinches, both in pressure balance [4] and in radiation balance [2,4], that stimulated the present study.Compression is rapid if the rate of compression is fast compared to the turbulent timescale τ = k/ with k the TKE and the viscous dissipation rate. In the initially rapid plasma compressions here, the viscous dissipation eventually grows such that the turbulent timescale τ shortens, and the plasma TKE suddenly dissipates. This dissipation is sudden in that it occurs over a time interval that is small compared to the overall compression time.This sudden dissipation mechanism now suggests a new fast ignition paradigm. Imagine an initially turbulent fusion fuel plasma where the majority of the energy is in the turbulent motion. This plasma is then rapidly compressed, causing both the TKE and thermal energy to grow, while the TKE retains most of the energy, as observed in certain Z-pinch experiments [1][2][3][4]. Since radiation losses (both synchrotron and bremsstrahlung) and nuclear fusion are dependent on thermal energy but not the TKE, those processes are minimized under such compression, since the plasma stays comparatively cool. However, late in the compression, the TKE suddenly dissipates viscously into thermal energy, thereby igniting the plasma without having undergone large radiation losses.In neutral gas, upon rapid compression, the TKE grows. In an isotropic 3D compression, it grows as 1/L 2 , where L is the (time dependent) side length of a box that is compressing with the mean flow along each axis. This is true for both the zero Mach case [7], where the TKE is solenoidal, as well as in the finite Mach case, where the TKE has both solenoidal and dilational components, which each grow in energy as 1/L 2 [12]. This is the same

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Sudden Viscous Dissipation of Compressing Turbulence

Davidovits

Fisch

2016

Phys. Rev. Lett.

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“…[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.…”

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

et al. 2011

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The performance of a metal puff Z-pinch system has been studied experimentally. In this type of system, the initial cylindrical shell 4 cm in diameter was produced by ten plasma guns. Each gun initiates a vacuum arc operating between magnesium electrodes. The net current of the guns was 80 kA. The arc-produced plasma shell was compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.3 cm in diameter was formed. The electron temperature of the plasma reached 400 eV at an average ion concentration of 1.85 Á 10 18 cm À3 . The power of the Mg K-line radiation emitted by the plasma for 15-30 ns was 300 MW=cm.

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“…This value is about 40% lower than the final implosion velocity obtained at r < 0.5 mm using X-ray imaging. This is expected since, in our experiments [3], [5], only ∼ =20% of the very leading edge of the imploding plasma constitutes the K-emitting portion of the stagnating plasma. …”

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Evolution of MHD Instabilities in Plasma Imploding Under Magnetic Field

Osin

Kroupp

Starobinets

et al. 2011

IEEE Trans. Plasma Sci.

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Abstract-Two-dimensional 3-ns-gated visible images, recorded at different times during the implosion of plasma under azimuthal magnetic field (Z-pinch), revealed ringlike instabilities followed by the development of axially and azimuthally nonuniform structures in the imploding plasma. Remarkably, the evolution in time of all structures was found to be highly repeatable in different shots, which should allow, through 3-D magnetohydrodynamics modeling, for systematically studying the development in time of these complex phenomena and correlating them with the initial plasma parameters. The data are also used to infer the time-dependent outer plasma radius and plasma radial velocities. Index Terms-Plasma implosion, visible imaging, Z-pinch.T HE Z-PINCH implosions serve as intense sources of X-ray radiation that are of broad interest in the research toward inertial confinement fusion and the study of matter under high energy density [1]. In such systems, a cylindrical plasma column (typically formed out of an array of fine wires or a puff of gas) radially implodes under the azimuthal magnetic field resulting from axially driven high currents. In this process, acceleration-driven instabilities play a major role in the magnetohydrodynamics (MHD) of the plasma, including causing complex current paths in the plasma, magnetic-field penetration into certain parts of the plasma, and nonuniform disturbances in the implosion [2].In this paper, a neon puff (∼70 µg/cm) was imploded in 500 ns until stagnation on axis under a current pulse that rises to 500 kA [3]. The puff consists of a 38-mm-diameter outer shell and an ∼5-mm-diameter on-axis jet. The distance between the cylindrical nozzle (which serves as the cathode) and the cylindrical anode was 9.5 mm. Planar laser-induced fluorescence measurements on a similar system, but with an additional cylindrical nozzle, showed that the azimuthal uniformity of the initial gas density distribution is better than ±15% [4]. An f/16 optics with 7.5× demagnification and coupled to an intensified CCD, viewing the plasma in the radial direction, provided a submillimeter spatial resolution across the 38-mm-diameter plasma shell, together with a sufficient signal. The filter used transmitted visible light above 6000 Å (T > 40%), thus mainly recording continuum radiation except for the earliest phase of the implosion where NeI-II line emission was significant too. The emission is thus nearly proportional to the square of the plasma density. The 3-ns-gated images were taken at different times along the implosion phase until the plasma stagnates on axis. Shown in Fig. 1 are 14 images of the imploding shell, most of them 50 ns apart, starting at t = −500 ns and ending at t = 0 (when the plasma stagnates on axis). Surprisingly, it was found that the complex structures evolving in the plasma are repeatable in the different shots. Their repeatability even allows for tracking the growth of the structures at specific z-locations down to t ∼ = −100 ns.The initial factors that govern the start of the ...

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Ion-Kinetic-Energy Measurements and Energy Balance in aZ-Pinch Plasma at Stagnation

Cited by 40 publications

References 11 publications

Sudden Viscous Dissipation of Compressing Turbulence

Sudden Viscous Dissipation of Compressing Turbulence

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

Evolution of MHD Instabilities in Plasma Imploding Under Magnetic Field

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