Different k{lambda}{sub D} regimes for nonlinear effects on Langmuir waves

Journal Article · Mon May 15 04:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2178777· OSTI ID:20783124

Kline, J L; Montgomery, D S; Yin, L; DuBois, D F; Albright, B J; Bezzerides, B; Cobble, J A; Dodd, E S; DuBois, D F; Fernandez, J C; Johnson, R P; Kindel, J M; Rose, H A; Vu, H X; Daughton, W ^[1]

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1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

As Langmuir waves (LWs) are driven to large amplitude in plasma, they are affected by nonlinear mechanisms. A global understanding, based on simulations and experiments, has emerged that identifies various nonlinear regimes depending on the dimensionless parameter k{lambda}{sub D}, where k is the Langmuir wave number and {lambda}{sub D} is the electron Debye length. The nonlinear phenomena arise due to wave-wave and wave-particle coupling mechanisms, and this basic separation between fluid-like nonlinearities and kinetic nonlinearities depends on the degree to which electron and ion Landau damping, as well as electron trapping, play a role. Previous ionospheric heating experiments [Cheung et al. Phys. Plasmas 8, 802 (2001)] identified cavitation/collapse and Langmuir decay instability (LDI), predominantly wave-wave mechanisms, to be the principal nonlinear effects for driven LWs with k{lambda}{sub D}<0.1, in agreement with fluid simulations [DuBois et al. Phys. Plasmas 8, 791 (2001)]. In the present research, collective Thomson scattering measurements of LWs driven by stimulated Raman scattering in laser-plasma experiments are used to study both wave-wave and wave-particle nonlinearities [Kline et al. Phys. Rev. Lett. 94, 175003 (2005)]. For k{lambda}{sub D}<0.29, multiple LWs are detected and are attributed to LDI, a wave-wave nonlinear regime. For k{lambda}{sub D}>0.29, a single-wave, frequency-broadened spectrum is observed associated with electron trapping, a wave-particle nonlinear regime. The transition from wave-wave to wave-particle nonlinear behavior is qualitatively consistent with particle-in-cell simulations and with the crossing of the LDI threshold above that for LW self-focusing. The fact that LDI is observed in both ionospheric and laser-plasma experiments for similar values of k{lambda}{sub D}, though vastly differing in plasma conditions and scales, and that simulations predict the various observed nonlinear regimes over a large range of k{lambda}{sub D}, supports our global view of LW nonlinear behavior.

• OSTI ID: 20783124
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 13; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AMPLITUDES
CAVITATION
COUPLING
DEBYE LENGTH
DECAY INSTABILITY
ELECTRONS
IONS
LANDAU DAMPING
LIGHT TRANSMISSION
NONLINEAR PROBLEMS
PLASMA
PLASMA DIAGNOSTICS
PLASMA HEATING
PLASMA SIMULATION
RAMAN EFFECT
THOMSON SCATTERING
TRAPPING