Investigation of ion temperature in low-density undercritical foams

Abstract The ion temperature in laser-heated foam materials can be considerably higher than the electron temperature due to the internal collisions of the plasma flows originating from the heterogeneous foam microstructure. Recently, we have developed a novel hybrid multiscale model for laser-foam interaction that successfully reproduces the experimentally measured heat front propagation in laser-heated subcritical foams of various densities. However, when applied to undercritical foams with average density closer to critical, the hybrid model simulations predict an ion–electron temperature ratio much larger than in any previously reported measurements and suggest that the influence of foam microstructure is more impactful for larger average densities. For such foams, the laser-driven heat front velocity was measured many times, but the ion temperature received much less attention. To investigate the ion temperature, the laser interaction with 10 mg <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mtext>cm</mml:mtext> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> undercritical chlorine-doped TMPTA foams has been studied at the PALS facility, using an extended diagnostic complex emphasizing the x-ray time-resolved studies of the plasma wave propagation inside the foam and the distribution of macroscopic plasma parameters via high-resolution x-ray spectroscopy. The ion and electron temperatures have been measured from Doppler broadening and the relative intensity ratio of chlorine x-ray spectral lines. The averaged ion and electron temperature ratio ranges from 2 to 4 depending on the laser pulse energy. The simulations agree reasonably well with the experimental results.