Hot-electron production and suprathermal heat flux scaling with laser intensity from the two-plasmon-decay instability

Journal Article · Mon Oct 15 00:00:00 EDT 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4757978· OSTI ID:22068828

Vu, H X ^[1]; DuBois, D F ^[2]; Myatt, J F ^[3]; Russell, D A ^[2]

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1. University of California, San Diego, La Jolla, California 92093 (United States)
2. Lodestar Research Corporation, Boulder, Colorado 80301 (United States)
3. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)

The fully kinetic reduced-description particle-in-cell (RPIC) method has been applied to simulations of two-plasmon-decay (TPD) instability, driven by crossed laser beams, in an inhomogeneous plasma for parameters consistent with recent direct-drive experiments related to laser-driven inertial fusion. The nonlinear saturated state is characterized by very spiky electric fields, with Langmuir cavitation occurring preferentially inside density channels produced by the ponderomotive beating of the crossed laser beams and the primary TPD Langmuir waves (LWs). The heated electron distribution function is, in all cases, bi-Maxwellian, with instantaneous hot-electron temperatures in the range 60-100 keV. The net hot-electron energy flux out of the system is a small fraction ({approx}1% to 2%) of the input laser intensity in these simulations. Scalings of the hot-electron temperature and suprathermal heat flux as functions of the laser intensity are obtained numerically from RPIC simulations. These simulations lead to the preliminary conclusion that Langmuir cavitation and collapse provide dissipation by producing suprathermal electrons, which stabilize the system in saturation and drive the LW spectrum to the small dissipation scales at the Landau cutoff. The Langmuir turbulence originates at an electron density 0.241 Multiplication-Sign the laser's critical density, where the crossed laser beams excite a 'triad' mode-a common forward LW plus a pair of backward LWs. Remnants of this 'triad' evolve in k-space and dominate the time-averaged energy spectrum. At times exceeding 10 ps, the excited Langmuir turbulence spreads toward lower densities. Comparisons of RPIC simulations with the extended Zakharov model are presented in appropriate regimes, and the necessary requirements for the validity of a quasi-linear Zakharov model (where the spatially averaged electron-velocity distribution is evolved) are verified by RPIC simulation results.

• OSTI ID: 22068828
• Journal Information: Physics of Plasmas, Vol. 19, Issue 10; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
DECAY INSTABILITY
DISTRIBUTION FUNCTIONS
ELECTRIC FIELDS
ELECTRON DENSITY
ELECTRON TEMPERATURE
ENERGY SPECTRA
HEAT FLUX
ICF DEVICES
INERTIAL FUSION DRIVERS
INHOMOGENEOUS PLASMA
LANGMUIR FREQUENCY
LASER-PRODUCED PLASMA
LASERS
NONLINEAR PROBLEMS
PHOTON BEAMS
PLASMONS
SCALING
TURBULENCE