Conceptual design of the gamma-to-electron magnetic spectrometer for the National Ignition Facility

• Published in: Review of scientific instruments Vol. 85; no. 11; p. 11E122
• Main Authors: Kim, Y, Herrmann, H W, Jorgenson, H J, Barlow, D B, Young, C S, Stoeffl, W, Casey, D, Clancy, T, Lopez, F E, Oertel, J A, Hilsabeck, T, Moy, K, Batha, S H
• Format: Journal Article
• Language: English
• Published: United States 01.11.2014
• ISSN: 1089-7623
• DOI: 10.1063/1.4892900

The Gamma-to-Electron Magnetic Spectrometer (GEMS) diagnostic is designed to measure the prompt γ-ray energy spectrum during high yield deuterium-tritium (DT) implosions at the National Ignition Facility (NIF). The prompt γ-ray spectrum will provide "burn-averaged" observables, including total DT fusion yield, total areal density (ρR), ablator ρR, and fuel ρR. These burn-averaged observables are unique because they are essentially averaged over 4π, providing a global reference for the line-of-sight-specific measurements typical of x-ray and neutron diagnostics. The GEMS conceptual design meets the physics-based requirements: ΔE/E = 3%-5% can be achieved in the range of 2-25 MeV γ-ray energy. Minimum DT neutron yields required for 15% measurement uncertainty at low-resolution mode are: 5 × 10(14) DT-n for ablator ρR (at 0.2 g/cm(2)); 2 × 10(15) DT-n for total DT yield (at 4.2 × 10(-5) γ/n); and 1 × 10(16) DT-n for fuel ρR (at 1 g/cm(2)).