Enhancement of X-Ray Power from a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">Z</mml:mi></mml:math>Pinch Using Nested-Wire Arrays

Deeney, C.; Douglas, M. R.; Spielman, R. B.; Nash, T. J.; Peterson, Darrell L.; L’Eplattenier, P.; Chandler, G. A.; Seamen, J. F.; Struve, K. W.

doi:10.1103/physrevlett.81.4883

Cited by 348 publications

(180 citation statements)

References 15 publications

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“…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.…”

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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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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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confidence: 99%

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

et al. 2012

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“…Achieving high x-ray powers by releasing this energy in a short time requires a high degree of azimuthal symmetry of the imploding plasma and a low level of initial axial perturbations seeding the growth of magnetic Rayleigh-Taylor (MRT) instabilities. The highest x-ray powers in z-pinch implosions were achieved using cylindrical arrays made of large numbers of fine metallic wires (280-300 TW, >2 MJ at ∼20% efficiency on the Z facility at SNL [1] [2]). Experimental studies of wire array z-pinches have shown [3] [4] [5] that even for large number of wires the arrays do not form a plasma shell imploding as a 2-D object.…”

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confidence: 99%

Suppression of the Ablation Phase in Wire Array Z Pinches Using a Tailored Current Prepulse

et al. 2011

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A new wire array configuration has been used to create thin shell-like implosions in a cylindrical array for the first time. The setup introduces a ∼5 kA, ∼25 ns current prepulse followed by a ∼140 ns current-free interval before the application of the main (∼1 MA) current pulse. The prepulse volumetrically heats the wires which expand to ∼1 mm diameter leaving no dense wire core and without development of instabilities. The main current pulse then ionises all the array mass resulting in suppression of the ablation phase, an accelerating implosion and no trailing mass. Rayleigh-Taylor instability growth in the imploding plasma is inferred to be seeded by µm-scale perturbations on the surface of the wires. The absence of wire cores is found to be the critical factor in altering the implosion dynamics.Fast z-pinch plasma implosions driven by multi megaAmpere currents are very efficient at converting stored electrical energy into X-rays. Achieving high x-ray powers by releasing this energy in a short time requires a high degree of azimuthal symmetry of the imploding plasma and a low level of initial axial perturbations seeding the growth of magnetic Rayleigh-Taylor (MRT) instabilities. The highest x-ray powers in z-pinch implosions were achieved using cylindrical arrays made of large numbers of fine metallic wires (280-300 TW, >2 MJ at ∼20% efficiency on the Z facility at SNL [1] [2]). Experimental studies of wire array z-pinches have shown [3] [4] [5] thateven for large number of wires the arrays do not form a plasma shell imploding as a 2-D object. Instead, the wires remain as discrete, compact objects for the first 60-80% of the implosion and during this time only the coronal plasma, continuously ablated from the stationary cores, are accelerated towards the axis by the J×B force [4]. This ablation phase determines the initial conditions for the implosion in two ways. Firstly, the ablated plasma fills the interior of the array which contributes to the mitigation of the growth of the MRT instability. Secondly, the quasi-periodic modulation of the ablation rate along each individual wire occurring at the 'natural' wavelength (∼250 μm for W and ∼500 μm for Al) is responsible for the large level of axial perturbations at the start of the implosion phase. The existence of the ablation phase is observed in all known wire array z-pinch experiments (currents between ∼1 MA and 26 MA, and implosion times between ∼50 ns and ∼800 ns) and occurs because current is initially carried by the small amount of plasma formed on the wire surfaces, and not by the wire cores themselves.In this letter we report on experiments where, for the first time, the ablation phase in wire array z-pinches was suppressed, including dramatic suppression of the axial perturbations in the wires and suppression of the precursor plasma flow. This was achieved by using a short duration low-level current pre-pulse (∼25 ns, ∼5 kA) followed by a ∼140 ns current-free interval before the main (∼1 MA, 100 ns) current pulse driving the implosion is applied. Th...

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“…The strongest laboratory X-ray source on Earth today is the Z Machine at Sandia National Laboratory, which routinely produces upwards of 100 TW (10 21 ergs/s) by driving 18 MA of electrical current through cylindrical arrays of 100-400 fine wires [7,8]. The array as a whole is some 20-70 mm in diameter and 10-20 mm tall to start with.…”

Section: Z Pinch X-ray Sources For Photoionizationmentioning

confidence: 99%

X-ray spectroscopy of astrophysically-relevant photoionized iron plasmas at Z

Heeter¹,

Bailey²,

Cuneo³

et al. 2000

AIP Conference Proceedings

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Abstract. In order to provide benchmark data for models used to interpret X-ray astronomy data from newly-launched orbital telescopes such as Chandra, we have used 120 TW, 180 eV pinch plasmas on the Sandia Z facility to drive iron foils into X-ray photoionized equilibrium. The experiment was designed to achieve photoionization parameters characteristic of accretion-powered objects such as X-ray binaries (neutron stars) and active galactic nuclei (black holes). These objects comprise roughly half of observed X-ray sources, but the interpretation of their spectra is difficult: stateof-the-art models for photoionized iron plasmas do not yet agree on the expected ionization balance. In our initial experiments the foil samples consisted of 200Å of iron codeposited with 300Å of sodium fluoride and sandwiched between two 1000Å layers of Lexan (CH and O). We characterized the pinch spectrum, temperature, power and uniformity and qualified it as a photoionization driver. We obtained time-integrated absorption spectra for the foil from 8 to 18Å and identified spectral lines from O VIII, F IX, Na X and XI, and Fe XVII and XVIII, i.e. neon-line and fluorine-like iron. Time-resolved absorption and emission spectra for the foils were also obtained from 12.5 to 16Å, and hydrogen-like F and neon-like and fluorine-like Fe were again observed in the 2 ns time window of interest. In subsequent ridealong experiments we have developed a density diagnostic and measured the density via foil-expansion imaging at two locations. We conclude by discussing upcoming experiments at Z in which we plan to obtain a full data set of plasma density, temperature, and absorption and emisssion spectra for multiple photoionization equilibria.

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Enhancement of X-Ray Power from aZPinch Using Nested-Wire Arrays

Cited by 348 publications

References 15 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

Suppression of the Ablation Phase in Wire Array Z Pinches Using a Tailored Current Prepulse

X-ray spectroscopy of astrophysically-relevant photoionized iron plasmas at Z

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