skip to main content

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

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 K{sub β}). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.
Authors:
;  [1] ; ; ; ; ; ; ; ; ;  [2] ;  [3]
  1. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)
  2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
  3. National Security Technologies LLC, Livermore, California 94551 (United States)
Publication Date:
OSTI Identifier:
22308583
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 11; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; BREMSSTRAHLUNG; ELECTRONS; FLUORESCENCE; GE SEMICONDUCTOR DETECTORS; HARD X RADIATION; IGNITION; INERTIAL CONFINEMENT; K SHELL; KEV RANGE; LASER RADIATION; PLASMA; RESPONSE FUNCTIONS; SENSITIVITY; SIGNAL-TO-NOISE RATIO; TIME RESOLUTION; US NATIONAL IGNITION FACILITY; X-RAY SOURCES; X-RAY SPECTROMETERS