Backlighter development at the National Ignition Facility (NIF): Zinc to zirconium

Development of a Big Area BackLighter for high energy density experiments

“…data with other NIF backlighter C.E.s (b) and Omega (a), which generally fall in the range of 0.2%-2% at NIF, making the BABL's 3.5% C.E. performance consistent with high drive (>100 kJ) x-ray source targets for NIF in the 3%-6% range, 22 and falls near the line fit to the "gas" targets which also fits the "pre-exploded foils" at Omega, 26 which range from 1% to 7%. The gas targets are generally noble gases in a Be "can" irradiated by several lasers similar to a hohlraum, 37 thus it should not be too surprising that "exploded targets," gas targets, and prepulse targets behave similarly in terms of laser absorption and conversion efficiency, as the underdense plasmas (or gas) allows more of the laser to interact with the target.…”

“…(a) C.E. of the Fe BABL compared to other experiments at Omega and Nova (adapted from Babonneau et al 26 ) and (b) at NIF and Omega (adapted from Barrios et al 22 ), leaving out the NIF Prepulse foils driven at too high or too low of a comparable intensity of 850 TW/cm 2 .…”

“…4 has a low intensity picket to preform a plasma to improve the conversion efficiency, especially that of the 23.5 • beams. 22,26 Each beam has ∼5.5 kJ, producing the total energy of ∼132 kJ on target with a peak power of 1.8 TW in the main pulse at a maximum intensity of 8.5 × 10 14 W/cm 2 . This intensity is empirically known to produce strong (>0.5% C.E.)…”

“…However, the story is evolving, given the greater than expected conversion efficiencies measured on NIF. 22 For backlit radiography along the polar axis, point projection has been demonstrated to work quite well by Cooper et al 23 In this geometry, there is a lot of flexibility in setting the distances between the backlighter, detector, and target. This geometry also allows for a large number of beams on the backlighter with good pointing accuracy.…”

“…4. The backlighter laser pulse shape following Ref 22,. which uses a prepulse picket to produce a small plasma to help increase laser absorption and thus conversion efficiency.…”