Titanium lined hohlraums as multi-keV x-ray converters

Developments of bright multi-keV K-shell emission sources [1-3] are necessary for ICF studies such as radiography of dense materials. Our recent works with prepulsed foils of titanium (He$_{\alpha }$ at 4.7~keV), copper (He$_{\alpha }$ at 8.3~keV) and germanium (He$_{\alpha }$ at 10.3~keV) showed high multi-keV x-ray conversion efficiencies up to 8.0{\%}, 1.0{\%} and 2.5{\%} (respectively) [1,2]. In comparison with thick foils, the preexploded foils conversion efficiencies are increased by a factor of more than 2. Hohlraums with a titanium liner have been used on the OMEGA laser facility in Rochester to quantify the multi-keV x-ray conversion. For the first time, a laser pulse with a picket prior to the main bulk of laser power has been employed with a Ti-lined hohlraum. X-ray produced with this laser pulse with picket is compared to the case with a square 1 ns pulse shape. X-ray power was measured by the broadband spectrometer DMX (filtered diodes) and the absolutely calibrated crystal spectrometer HENWAY. Multi-keV emission is diagnosed by a full set of diagnostics giving conversion efficiencies, time dependant x-ray power and imaging, time integrated imaging and high resolution spectra of titanium. [1] F. Girard et al., Phys. Plasmas, \textbf{12}, 092705 (2005) [2] D. Babonneau et al., submitted in Phys. Rev. Lett. [3] K. B. Fournier et al., Phys. Rev. Lett., \textbf{92}, 165005 (2004)