부산대학교 도서관

We have measured the production of h{nu} {approx}> 4.5 keV x-rays from low-density Ti-doped aerogel targets at the OMEGA laser facility (University of Rochester). The targets were 2.2 mm long by 2 mm diameter beryllium cylinders filled with Ti-doped (3 atomic percent) SiO{sub 2} foam. The doped-foam density was {approx} 3 mg/cc. Forty beams of the OMEGA laser ({gamma} = 351 nm) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser interaction fully ionizes the target (n{sub e}/n{sub crit} {approx}< 0.1), and allows the laser-bleaching wave to excite, supersonically, the high-Z emitter ions in the sample. The heating of the target was imaged with a gated (200 ps time resolution) x-ray framing camera filtered to observe > 4 keV. 2-D radiative hydrodynamic calculations predict rapid and uniform heating over the whole target volume with minimal energy losses into hydrodynamic motion. An x-ray streak camera, also filtered to observe > 4 keV, was used to measure the rate of heat propagation in the target. Ti K-shell x-ray emission was spectrally resolved with a two-channel crystal spectrometer and recorded with a set of calibrated aluminum x-ray diodes. Back-scattered laser energy is observed to be minimal. We find between 100 - 400 J of output with 4.67 {approx}< h{nu} {approx}<{approx}< 5.0 keV, predicted target performance is a factor of 2 - 3 too low in this range.