Surface heating of wire plasmas using laser-irradiated cone geometries

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Petawatt lasers can generate extreme states of matter, making them unique tools for high-energy-density physics. Pressures in the gigabar regime can potentially be generated with cone-wire targets when the coupling efficiency is high and temperatures reach 2–4 keV (ref. 1). The only other method of obtaining such gigantic pressures is to use the megajoule laser facilities being constructed (National Ignition Facility and Laser MégaJoule). The energy can be transported over surprisingly long distances but, until now, the guiding mechanism has remained unclear. Here, we present the first definitive experimental proof that the heating is maximized close to the wire surface, by comparison of interferometric measurements with hydrodynamic simulations. New hybrid particle-in-cell simulations show the complex field structures for the first time, including a reversal of the magnetic field on the inside of the wire. This increases the return current in a spatially separated thin layer below the wire surface, resulting in the enhanced level of ohmic heating. There are a significant number of applications in high-energy-density science, ranging from equation-of-state studies to bright, hard X-ray sources, that will benefit from this new understanding of energy transport.

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Figure 1: Interferogram of a cone-wire target that was used to calculate plasma densities from the observed phase shifts.
Figure 2: A comparison of computational and experimental radial density profiles for 7-μm-diameter copper wire 400 μm from the cone tip.
Figure 3: LSP modelling of the azimuthal magnetic field structure at the cone tip, 600 fs after the main interaction.
Figure 4: LSP modelling of the net current density inside the wire, 600 fs after the main interaction.


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This work was supported by the UK Engineering and Physical Sciences Research Council and the Science and Technology Facilities Council. American colleagues acknowledge support from the US Department of energy contract number W-7405-Eng-48. Japanese colleagues acknowledge the Japan Society for the Promotion of Science. The authors gratefully acknowledge the support of the staff of the Central Laser Facility.

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F.N.B., R.R.F., J.S.G., M.H.K., R.K., K.L.L., P.A.N., R.S. and L.V.W. were all involved in project planning. J.S.G. and P.A.N. carried out the data analysis and wrote the letter. All other named authors contributed to the experimental work and corrected the manuscript.

Correspondence to P. A. Norreys.

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