Time-resolved measurements of the hot-electron population in ignition-scale experiments on the National Ignition Facility (invited)

Journal Article · Thu Jul 24 00:00:00 EDT 2014 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4890537· OSTI ID:1144747

Hohenberger, M. ^[1]; Albert, F. ^[2]; Palmer, N. E. ^[2]; Lee, J. J. ^[3]; Döppner, T. ^[2]; Divol, L. ^[2]; Dewald, E. L. ^[2]; Bachmann, B. ^[2]; MacPhee, A. G. ^[2]; LaCaille, G. ^[2]; Bradley, D. K. ^[2]; Stoeckl, C. ^[1]

---

1. University of Rochester 1 Laboratory for Laser Energetics, , Rochester, New York 14623, USA
2. Lawrence Livermore National Laboratory 2 , Livermore, California 94550, USA
3. National Security Technologies LLC 3 , Livermore, California 94551, USA

In laser-driven inertial confinement fusion, hot electrons can preheat the fuel and prevent fusion-pellet compression to ignition conditions. Measuring the hot-electron population is key to designing an optimized ignition platform. The hot electrons in these high-intensity, laser-driven experiments, created via laser-plasma interactions, can be inferred from the bremsstrahlung generated by hot electrons interacting with the target. At the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)], the filter-fluorescer x-ray (FFLEX) diagnostic–a multichannel, hard x-ray spectrometer operating in the 20–500 keV range–has been upgraded to provide fully time-resolved, absolute measurements of the bremsstrahlung spectrum with ∼300 ps resolution. Initial time-resolved data exhibited significant background and low signal-to-noise ratio, leading to a redesign of the FFLEX housing and enhanced shielding around the detector. The FFLEX x-ray sensitivity was characterized with an absolutely calibrated, energy-dispersive high-purity germanium detector using the high-energy x-ray source at NSTec Livermore Operations over a range of K-shell fluorescence energies up to 111 keV (U Kβ). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.

• Research Organization: Univ. of Rochester, NY (United States). Lab. for Laser Energetics
• Sponsoring Organization: USDOE
• DOE Contract Number: NA0001944
• OSTI ID: 1144747
• Report Number(s): DOE/NA/0001944-1185; 2014-14; 2152
• Journal Information: Review of Scientific Instruments, Vol. 85, Issue 11; ISSN 0034-6748
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English