Steady-state radiation ablation in the wire-array Z pinch

Yu, Edmund; Oliver, B.V.; Sinars, Daniel Brian; Mehlhorn, T. A.; Cuneo, M. E.; Sasorov, P. V.; Haines, M. G.; Lebedev, S. V.

doi:10.1063/1.2435332

Cited by 58 publications

(50 citation statements)

References 43 publications

(27 reference statements)

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“…Numerical 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.…”

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

et al. 2012

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“…Liquid metal expands in the form of submicron drops surrounded by vapor [14]. The melted parts of the wire expand and ablate faster than its solid parts, because the ablation rate is proportional to the ablating surface [15]. In contrast, an axially uniform homogeneous ablation has been observed from wire cores that were totally in a hot liquid state at breakdown [5].…”

Section: Ablation Symmetry Vs Core Conditionmentioning

confidence: 90%

New paradigm : controlling initiation phase is necessary for optimization of wire-array z-pinch performance.

Rosenthal¹,

Sarkisov

Sanford³

2008

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The initiation phase of a wire-array is of paramount importance for achieving an axially homogeneous z-pinch and reproducible, high x-ray power. The significance of wire-array initiation during current prepulse for z-pinch performance has not been widely acknowledged. To achieve new levels of progress in wire-array z-pinch physics it is necessary to accept the importance of initiation physics, and to implement diagnostics of array initiation. This communication provides a brief review pointing out the need to control the initiation phase of a wire array for optimum z-pinch performance, and suggesting why multi-MA wire-array z-pinch experiments fail to meet MHD expectations.

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“…• Wire ablation mechanisms [5] dominate the early time behavior of the Z-pinch and control the implosion dynamics, which determines the shape of the radiation pulse. Because wire ablation simulations need extreme resolution, they have been limited to single wires in 3D or a just few wires in 2D.…”

Section: Unresolved Science Questionsmentioning

confidence: 99%

Estimating Z-Pinch computing resources.

Brunner

2007

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The Z facility at Sandia National Laboratories produces high energy density environments. Computer simulations of the experiments provide key insights and help make the most efficient use of the facility. This document estimates the computer resources needed in order to support the experimental program. The resource estimate is what we would like to have in about five years and assumes that we will have a robust, scalable simulation capability as well as enough physicists to run the simulations. 3 AcknowledgmentsMany people have contributed to this document, suggesting editorial changes, helping provide the computing estimates, or providing the background of why the simulations are needed in the first place. These people are:

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Steady-state radiation ablation in the wire-array Z pinch

Cited by 58 publications

References 43 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

New paradigm : controlling initiation phase is necessary for optimization of wire-array z-pinch performance.

Estimating Z-Pinch computing resources.

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