Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Kα radiation generated by interaction of an ultrashort (1 ps) laser with thin (25 μm) Ti foils at high intensity (2× 1016 W cm2) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of Kα brightness. Laser to Kα and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75±2%. Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high Kα yield. This is attributed to a shift in the K -shell spectrum due to Ti ionization. © 2005 American Institute of Physics.

Abstract:

We propose a new mechanism for anomalous ion heating in ultraintense laser plasmas. This mechanism is based on the excitation of an electron two-stream instability that is driven by the fast electron beam that resonantly decays into ion-acoustic waves. These low frequency waves are then strongly damped by the ion collisions in the dense plasma. The model gives a simple explanation for the preferential heating of the bulk ion population observed in recent laser experiments in the petawatt regime. In particular, this work provides an explanation for the different energy loss in the Au and CD plasmas, in cone-guided fast ignition experiments. © 2005 The American Physical Society.