Diagnosing ICF gamma-ray physics [electronic resource].
- Washington, D.C. : United States. Dept. of Energy, 2010. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Additional Creators:
- Los Alamos National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
- Restrictions on Access:
- Free-to-read Unrestricted online access
- Gamma rays produced in an ICF environment open up a host of physics opportunities we are just beginning to explore. A branch of the DT fusion reaction, with a branching ratio on the order of 2e-5 γ/n, produces 16.7 MeV γ-rays. These γ-rays provide a direct measure of fusion reaction rate (unlike x-rays) without being compromised by Doppler spreading (unlike neutrons). Reaction-rate history measurements, such as nuclear bang time and burn width, are fundamental quantities that will be used to optimize ignition on the National Ignition Facility (NIF). Gas Cherenkov Detectors (GCD) that convert fusion γ-rays to UV/visible Cherenkov photons for collection by fast optical recording systems established their usefulness in illuminating ICF physics in several experimental campaigns at OMEGA. Demonstrated absolute timing calibrations allow bang time measurements with accuracy better than 30 ps. System impulse response better than 95 ps fwhm have been made possible by the combination of low temporal dispersion GCDs, ultra-fast microchannel-plate photomultiplier tubes (PMT), and high-bandwidth Mach Zehnder fiber optic data links and digitizers, resulting in burn width measurement accuracy better than 10ps. Inherent variable energy-thresholding capability allows use of GCDs as γ-ray spectrometers to explore other interesting nuclear processes. Recent measurements of the 4.44 MeV ¹²C(n,n′) γ-rays produced as 14.1 MeV DT fusion neutrons pass through plastic capsules is paving the way for a new CH ablator areal density measurement. Insertion of various neutron target materials near target chamber center (TCC) producing secondary, neutron-induced γy-rays are being used to study other nuclear interactions and as in-situ sources to calibrate detector response and DT branching ratio. NIF Gamma Reaction History (GRH) diagnostics, based on the GCD concept, are now being developed based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF-specific logistics, requirements and extreme radiation environment. Implementation will occur in two phases: (1) four PMT-based channels mounted to the outside of the target chamber at ≈6m from TCC (GRH-6m) for the 3e13-3e16 DT neutron yield range expected during the early ignition-tuning campaigns; and (2) several channels located just inside the target bay shield wall at 15 m from TCC (GRH-15m) with optical paths leading through the cement shield wall to well-shielded streak cameras and PMTs for the 1e16-1e20 yield range expected during the DT ignition campaign. Multiple channels at each phase will allow for increased redundancy, reliability, accuracy and flexibility. This suite of diagnostics will make possible exploration of interesting γ-ray physics well beyond the ignition campaign.
- Published through SciTech Connect., 01/01/2010., "la-ur-10-03230", " la-ur-10-3230", 18th High Temperature Plasma Diagnostics Conference ; May 16, 2010 ; Wildwood, NH., and Herrmann, Hans W; Kim, Y H; Young, C S; Mack, J M; Wilson, D C; Langenbrunner, J R; Evans, S; Sedillo, T; Dauffy, L; Kaufman, M I; Cox, B C; Stoeffl, W; Horsfield, C J; Mc Evoy, A; Hoffman, N; Batha, S H; Malone, R; Tunnel, T W; Miller, E K; Ali, Z A; Rubery, M.
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