The dynamics of wire array Z-pinch implosions

Lebedev, S. V.; Aliaga-Rossel, R.; Bland, S. N.; Chittenden, J. P.; Dangor, A. E.; Haines, M. G.; Mitchell, I. H.

doi:10.1063/1.873456

Cited by 105 publications

(73 citation statements)

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“…The significantly higher precursor ion temperature indicates a higher flow velocity of the streams arriving on axis at early times, requiring an ion kinetic energy of 30 keV for a 20 keV ion temperature (assuming E ion = 3 2 κT ion ) corresponding to a velocity of V=1.75±0.22×10 7 cm/s. This is closer to the velocity of 1.5×10 7 cm/s which was previously found from the end-on measurements [6] of the motion of the first plasma ablated from the wires. This suggests that there is a decrease of the flow velocity with time at the beginning of the ablation phase, similar to what is seen in simulations (Fig.…”

Section: Fig 2: (A)supporting

confidence: 58%

“…The ablation mass distribution depends on the ablation rate, dm/dt, and on the flow velocity, which are related via force -momentum balance. However, the flow velocity was not measured in past experiments apart from the velocity of the initial part of the flow which was inferred from the time of plasma appearance on the array axis and from end-on interferometry measurements, giving V∼1.5×10 7 cm/s [6] [7]. The velocity of the ablation flow in the later stages, when the majority of the ablated material is moving into the array interior, is not known.…”

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confidence: 99%

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Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

et al. 2012

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A Thomson scattering diagnostic has been used to measure the parameters of cylindrical wire array Z pinch plasmas during the ablation phase. The scattering operates in the collective regime (α>1) allowing spatially localised measurements of the ion or electron plasma temperatures and of the plasma bulk velocity. The ablation flow is found to accelerate towards the axis reaching peak velocities of 1.2-1.3×10 7 cm/s in aluminium and ∼1×10 7 cm/s in tungsten arrays. Precursor ion temperature measurements made shortly after formation are found to correspond to the kinetic energy of the converging ablation flow.Wire array Z pinch implosions can efficiently convert stored electrical energy into powerful bursts of soft xrays. Experiments on the 20 MA Z pulsed power generator [1] have achieved peak powers of 280-300 TW with a >2 MJ yield at 20% efficiency [2] by imploding cylindrical arrays consisting of hundreds of fine metallic wires. It was found [3][4][5] that in wire array Z pinches the wires remain stationary for the first 60-80% of the implosion time and steadily ablate plasma which is accelerated by the j×B force. This ablation flow distributes mass in the array interior which sets the initial conditions for the implosion phase. The ablation mass distribution depends on the ablation rate, dm/dt, and on the flow velocity, which are related via force -momentum balance. However, the flow velocity was not measured in past experiments apart from the velocity of the initial part of the flow which was inferred from the time of plasma appearance on the array axis and from end-on interferometry measurements, giving V∼1.5×10 7 cm/s [6] [7]. The velocity of the ablation flow in the later stages, when the majority of the ablated material is moving into the array interior, is not known. Instead, the ablation rate and mass redistribution is often discussed using the so-called 'ablation velocity', introduced in the rocket model [3] via momentum balance arguments, which is inferred from the implosion dynamics or from unfolds of x-ray radiography measurements of mass distribution in the array interiorNumerical simulations [10][11] show that velocity is changing both with time and with the radial position of the flow, indicating that the flow is accelerated by the j×B force acting on the plasma in the array interior. However, these simulations do not model the initial heating of the wires and the process of conversion of initially cold metallic wires into a plasma. Instead, simulations start from wire material already converted into plasma at some initial temperature and density, and these initial conditions are adjusted to produce agreement of the simulated implosion dynamics with experimental observations. Direct measurements of the ablation flow velocity and density are needed to allow verification of these numerical models. Knowledge of the flow velocity is also important for other applications of different wire array Z pinch configurations, used e.g. in laboratory astrophysics [12] and other HEDP basic science research.In th...

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Section: Fig 2: (A)supporting

confidence: 58%

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confidence: 99%

Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

et al. 2012

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“…This orientation also suits the geometry of the wire array, as, apart from the "fundamental" modulation of the ablation rate, the dynamics are fairly axially uniform. While end on shadowgraphy and interferometry diagnostics have be fielded in previous experiments, 3,6,13,14 the work presented in this paper represents a significant improvement, both in terms of the apparatus used and the analysis techniques employed.…”

Section: Introductionmentioning

confidence: 98%

“…The experimental hardware was modified in order to provide better access for the end-on probing beam. In previous experiments, 3,6 a MichelsonMorley type probing arrangement has been used; the probing beam was directed down the axis of the array and reflected back through the array by a mirror mounted in the base of the cathode. The probing beam thus made two passes of the plasma.…”

Section: A Apparatusmentioning

confidence: 99%

“…The breaks form at this time due to the highly non-uniform ablation rate along the length of the wires; the ablation rate is modulated at a predictable "fundamental" wavelength. 6,7 Once the wires are broken the array undergoes a snowplough like implosion, 8,9 followed by the stagnation of the accrued kinetic energy as an intense pulse of soft x-ray radiation. 10,11 This paper presents the results of a series of experiments conducted in order to investigate the dynamics of wire array plasmas during the ablation phase.…”

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Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

et al. 2013

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A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by a dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M ¼ 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al. [Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT e of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well. V C 2013 American Institute of Physics. [http://dx

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Heterogeneous Plasma‐Producing Structures at Current Implosion of a Wire Array

Grabovsky

Mitrofanov

Nedoseev

et al. 2005

Contrib. Plasma Phys.

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Characteristic properties of the plasma production process have been considered for the case of megampere currents flowing through hollow cylindrical wire arrays of the Angara-5-1 facility. In 3-4 nanoseconds after voltage applying to the wire surfaces there appear a plasma layer. The system becomes heterogeneous, i.e. consisting of a kernel of metal wires and a plasma layer. In several nanoseconds the current flow goes from metal to plasma, which results in reducing the electric field strength along the wire.The Joule heat energy delivered to the metal before the moment of complete current trapping by plasma is insufficient for the whole mass transition to a hot plasma state. The X-ray radiography techniques made it possible to detect and study dense clusters of substance of ∼1g/cm 3 at a developed discharge stage. The radial expansion velocity of ∼10 4 cm/s measured at the 70-th nanosecond after the current start allows treating the dense core at a late stage in the form of a submicron heterogeneous structure from its liquid and slightly ionized gas phase.

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The dynamics of wire array Z-pinch implosions

Cited by 105 publications

References 23 publications

Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

Heterogeneous Plasma‐Producing Structures at Current Implosion of a Wire Array

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