X-ray continuum as a measure of pressure and fuel–shell mix in compressed isobaric hydrogen implosion cores

Journal Article · Sun Feb 01 00:00:00 EST 2015 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4907667· OSTI ID:1176906

Epstein, R.  ^[1]; Goncharov, V. N. ^[1]; Marshall, F. J. ^[1]; Betti, R. ^[2]; Nora, R. ^[2]; Christopherson, A. R. ^[2]; Golovkin, I. E. ^[3]; MacFarlane, J. J. ^[3]

---

1. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623, USA
2. Fusion Science Center and Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623, USA
3. Prism Computational Sciences, Madison, Wisconsin 53711, USA

Pressure, by definition, characterizes the conditions within an isobaric implosion core at peak compression [Gus’kov et al., Nucl. Fusion 16, 957 (1976); Betti et al., Phys. Plasmas 8, 5257 (2001)] and is a key parameter in quantifying its near-ignition performance [Lawson, Proc. Phys. Soc. London, B 70, 6 (1957); Betti et al., Phys. Plasmas 17, 058102 (2010); Goncharov et al., Phys. Plasmas 21, 056315 (2014); and Glenzer et al., Phys. Plasmas 19, 056318 (2012)]. At high spectral energy, where the x-ray emission from an imploded hydrogen core is optically thin, the emissivity profile can be inferred from the spatially resolved core emission. This emissivity, which can be modeled accurately under hot-core conditions, is dependent almost entirely on the pressure when measured within a restricted spectral range matched to the temperature range anticipated for the emitting volume. In this way, the hot core pressure at the time of peak emission can be inferred from the measured free-free emissivity profile. The pressure and temperature dependences of the x-ray emissivity and the neutron-production rate explain a simple scaling of the total filtered x-ray emission as a constant power of the total neutron yield for implosions of targets of similar design over a broad range of shell implosion isentropes. This scaling behavior has been seen in implosion simulations and is confirmed by measurements of high-isentrope implosions [Sangster et al., Phys. Plasmas 20, 056317 (2013)] on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)]. Attributing the excess emission from less-stable, low-isentrope implosions, above the level expected from this neutron-yield scaling, to the higher emissivity of shell carbon mixed into the implosion’s central hot spot, the hot-spot “fuel–shell” mix mass can be inferred.

• Research Organization: Univ. of Rochester, NY (United States). Lab. for Laser Energetics
• Sponsoring Organization: USDOE
• Grant/Contract Number: NA0001944
• OSTI ID: 1176906
• Journal Information: Physics of Plasmas, Vol. 22, Issue 2; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
70 PLASMA PHYSICS AND FUSION TECHNOLOGY