Historical research guide · 1041 · 2007
Steady-state radiation ablation in the wire-array Z pinch
Edmund P. Yu · Bryan V. Oliver · Daniel B. Sinars · Thomas A. Mehlhorn · Michael E. Cuneo · Pavel V. Sasorov · Malcolm G. Haines · Sergey V. Lebedev
In one minute
A wire-array Z pinch begins as a cage of hair-fine wires strung around a common axis. Millions of amps are pushed through the cage, and before anything implodes each wire spends most of the shot quietly boiling: a cold dense core survives while plasma streams off it toward the axis. How fast that boiling runs — the mass ablation rate — sets what happens next. Edmund Yu and his Sandia colleagues, with Pavel Sasorov in Moscow and Malcolm Haines and Sergey Lebedev at Imperial College London, treat the boiling as a steady state and simulate it in the plane cut across the array. By naming the mechanisms that actually carry energy to the wire, they derive a simple scaling law tying the ablation rate to the drive current, for the case where radiation rather than conduction delivers the heat. They then strip the problem to an analytical model — a wire core sitting in a heat bath, ablating because it is irradiated — to find how the rate depends on core size, and put model, simulation and experiment side by side.
Connection
Chapter 9 is about plasma that organises itself into current-carrying structures, and the ablation phase is where a wire array decides what structure it will implode as; chapter 12 depends on the same machines, because wire arrays drive the largest laboratory X-ray sources built for fusion, and the mass ablation rate is the number every one of those designs is built on.
From the source
The mass ablation phase of a wire-array Z pinch can be treated as a steady state and studied that way: the paper investigates it using steady-state simulations in the (r,θ) plane, the plane cut across the array rather than along its axis.Abstract, first sentence
The ablation process is governed by a small set of dominant physical mechanisms, and identifying them is what makes the problem tractable — the paper’s scaling result follows from that identification rather than from a fit to data.Abstract, second sentence
A simple scaling relation is derived linking the mass ablation rate ṁ to the drive current I, for the case where radiation is the primary energy transport mechanism carrying heat to the wire core.Abstract, second sentence
The dependence of the ablation rate on the size of the surviving wire core is investigated with a simplified analytical model — a wire core placed in a heat bath and ablating because it is being irradiated — rather than by simulation alone.Abstract, third sentence
The three lines of evidence are put against one another: results of the model, the simulation and the experiment are compared, so the analytical scaling is tested rather than asserted.Abstract, closing sentence
What to watch is the boundary of the radiation-dominated case the scaling is derived for. The measurement that would settle where it ends is an ablation-rate campaign that walks the drive current and the wire material across the point at which conduction, rather than radiation, becomes the channel carrying energy to the core, and shows whether the current scaling bends there.Abstract, second sentence, read against its own stated condition
The way in
https://doi.org/10.1063/1.2435332How to cite it
Edmund P. Yu, Bryan V. Oliver, Daniel B. Sinars, Thomas A. Mehlhorn, Michael E. Cuneo, Pavel V. Sasorov, Malcolm G. Haines, Sergey V. Lebedev (2007) Steady-state radiation ablation in the wire-array Z pinch doi:10.1063/1.2435332