Nonlinear development of the two-plasmon decay instability in three dimensions

Journal Article · Mon Apr 21 00:00:00 EDT 2014 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4871717· OSTI ID:1132847

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

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1. University of California 1 , San Diego, La Jolla, California 92093, USA
2. Lodestar Research Corporation 2 , Boulder, Colorado 80301, USA
3. Laboratory for Laser Energetics, University of Rochester 3 , Rochester, New York 14623, USA;University of Rochester 4 Department of Mechanical Engineering, , Rochester, New York 14627, USA

Most recent experiments on the excitation of the two plasmon-decay (TPD) instability involve a three-dimensional (3D) array of overlapping laser beams. Our recent two dimensional (2D) simulations suggested that Langmuir cavitation and collapse are important nonlinear saturation mechanisms for TPD. There are important quantitative differences in the Langmuir collapse process in 2D and 3D. To address these and other issues, we have developed a 3D Zakharov code. It has been applied to study the evolution of TPD from absolute instabilities (arising from 3D laser geometries) to the nonlinear state (J. Zhang et al., Phys. Rev. Lett. (submitted)). The present paper concentrates on the nonlinear saturated state excited by the collective action of two crossed laser beams with arbitrary polarizations. Remarkable agreement between 3D and 2D simulations is found for several averaged physical quantities when the beams are polarized in their common plane. As in the previous 2D simulations, we find: (a) the collective, initially convectively unstable triad modes dominate after a sub-picosecond burst, (b) Langmuir cavitation and collapse are important nonlinearities, and (c) that the statistics of intense cavitons are characteristic of a Gaussian random process. The 3D steady-state saturated Langmuir energy level is about 30% higher than in 2D. The auto-correlation functions of the Langmuir envelope field and of the low-frequency electron density field yield the spatial shape of the strongest collapsing cavitons which are 3D ellipsoids whose orientation depends on the laser polarizations. This tilting of the caviton's strongest electric field direction away from the normal to the target surface is a major new 3D result. This tilting may deflect the hot electron flux and thereby mitigate target preheat.

• Research Organization: Univ. of Rochester, NY (United States). Lab. for Laser Energetics
• Sponsoring Organization: USDOE
• DOE Contract Number: NA0001944
• OSTI ID: 1132847
• Report Number(s): DOE/NA/1944-1175; 2014-6; 2141
• Journal Information: Physics of Plasmas, Vol. 21, Issue 4; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English