Abstract
The Z-backlighter laser facility primarily consists of two high energy, high-power laser systems. Z-Beamlet laser (ZBL) (Rambo et al., Appl. Opt. 44, 2421 (2005)) is a multi-kJ-class, nanosecond laser operating at 1054 nm which is frequency doubled to 527 nm in order to provide x-ray backlighting of high energy density events on the Z-machine. Z-Petawatt (ZPW) (Schwarz et al., J. Phys.: Conf. Ser. 112, 032020 (2008)) is a petawatt-class system operating at 1054 nm delivering up to 500 J in 500 fs for backlighting and various short-pulse laser experiments (see also Figure 10 for a facility overview). With the development of the magnetized liner inertial fusion (MagLIF) concept on the Z-machine, the primary backlighting missions of ZBL and ZPW have been adjusted accordingly. As a result, we have focused our recent efforts on increasing the output energy of ZBL from 2 to 4 kJ at 527 nm by modifying the fiber front end to now include extra bandwidth (for stimulated Brillouin scattering suppression). The MagLIF concept requires a well-defined/behaved beam for interaction with the pressurized fuel. Hence we have made great efforts to implement an adaptive optics system on ZBL and have explored the use of phase plates. We are also exploring concepts to use ZPW as a backlighter for ZBL driven MagLIF experiments. Alternatively, ZPW could be used as an additional fusion fuel pre-heater or as a temporally flexible high energy pre-pulse. All of these concepts require the ability to operate the ZPW in a nanosecond long-pulse mode, in which the beam can co-propagate with ZBL. Some of the proposed modifications are complete and most of them are well on their way.
Highlights
Magnetized liner inertial fusion (MagLIF) is an approach for thermonuclear fusion that is driven by Sandia’s Z pulsed power facility[1]
Given Z-Beamlet laser (ZBL)’s comparatively small size and the conceptual simplicity afforded by its pulse formats and single-frequency phase modulation (PM), we concluded that a suitable PM failsafe design could be based on monitoring a single parameter, namely continuous detection of an optical heterodyne signal
Z-beamlet is still mostly used as a backlighter laser and in this case we have shown that the conversion efficiency into x-rays is dramatically improved when the adaptive optics (AO) system is used
Summary
ZBL operated at 2 kJ energy at 527 nm with 2 ns pulsewidth. This was sufficient for its primary backlighting mission, but it will not be enough for future laser heating requirements for MagLIF. ZBL’s single-frequency front-end laser was replaced with a phase modulation (PM) system that required development of a PM failsafe system. Even with these enhancements ZBL’s front end remains relatively simple compared to the multipulse, multi-frequency modulation used on systems such as OMEGA EP[5], NIF[6], LMJ[7] and the SG-III laser[8]
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