Efficient Multi-keV X-Ray Sources from Ti-Doped Aerogel Targets

We have measured the production of hv ∼ 4.7 keV x-rays from low-density Ti-doped aerogel (ρ ∼ 3 mg/cc) targets at the OMEGA laser facility (University of Rochester), with the goal of maximizing x-ray output. Forty OMEGA beams (λL = 0.351 (micro)m) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser fully ionizes the target (ne/ncrit (le) 0.1), and a laser-bleaching wave excites, supersonically, the high-Z emitter ions in the sample. Heating in the target was imaged with gated x-ray framing cameras and an x-ray streak camera. Ti K-shell x-ray emission was spectrally resolved with a two-channel crystal spectrometer and also with a set of filtered aluminum x-ray diodes, both instruments provide absolute measurement of the multi-keV x-ray emission. We find between 40 - 260 J of output with 4.67 (le) hv (le) 5.0 keV. Radiation-hydrodynamic calculations predict late time enhancement of the x-ray power due first to axial stagnation of the heating waves, then, ablatively-driven radial compression from the target walls