Ultrafast Melting of Carbon Induced by Intense Proton Beams

Laser-produced proton beams have been used to achieve ultrafast volumetric heating of carbon samples at solid density. The isochoric melting of carbon was probed by a scattering of x rays from a secondary laser-produced plasma. From the scattering signal, we have deduced the fraction of the material that was melted by the inhomogeneous heating. The results are compared to different theoretical approaches for the equation of state which suggests modifications from standard models.

Figure 1

Schematic layout: a polycrystalline graphite rod ($125\mu \mathrm{m}\times 300\mu \mathrm{m}\times 3\mathrm{mm}$) is heated by the protons produced by the laser coming from the lower left. The second laser hits a titanium foil to produce an intense x-ray pulse which is scattered off the green region of the sample and detected by a spectrometer above the target at 90°. The gold shielding blocks the line of sight from the laser spots to the scattering spectrometer as well as the front and back regions of the carbon rod. The RCF proton detector and the source radiation spectrometer are not shown.

Figure 2

Samples of RCF used to monitor the proton beam. A picture taken with the full target (left) shows the regions that are blocked by the target mount and the carbon sample. The right panel shows the whole proton beam taken without a target. The lines originate from a structure on the backside of the foil. They were used to determine the source size.

Figure 3

Temperature profile along the axis together with the energy spectrum of the protons used for this simulation. The total energy deposited in the carbon sample is 180 mJ. The grey (green) area marks the region probed by x-ray scattering.

Figure 4

(a) Ratio of the measured scattering intensity of heated and unheated graphite versus the energy that was deposited in the probed volume. (b) Fraction of molten carbon in the probed volume versus energy input. Experimental data are compared to theoretical modeling based on the SESAME EOS tables for carbon and the DFT-MD model.