Computational hydrodynamics and optical performance of inductively-coupled plasma adaptive lenses

Journal Article · Mon Jun 15 00:00:00 EDT 2015 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4922477· OSTI ID:22494167

Mortazavi, M.; Mani, A. ^[1]

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1. Center for Turbulence Research, Stanford University, Stanford, California 94305-3024 (United States)

This study addresses the optical performance of a plasma adaptive lens for aero-optical applications by using both axisymmetric and three-dimensional numerical simulations. Plasma adaptive lenses are based on the effects of free electrons on the phase velocity of incident light, which, in theory, can be used as a phase-conjugation mechanism. A closed cylindrical chamber filled with Argon plasma is used as a model lens into which a beam of light is launched. The plasma is sustained by applying a radio-frequency electric current through a coil that envelops the chamber. Four different operating conditions, ranging from low to high powers and induction frequencies, are employed in the simulations. The numerical simulations reveal complex hydrodynamic phenomena related to buoyant and electromagnetic laminar transport, which generate, respectively, large recirculating cells and wall-normal compression stresses in the form of local stagnation-point flows. In the axisymmetric simulations, the plasma motion is coupled with near-wall axial striations in the electron-density field, some of which propagate in the form of low-frequency traveling disturbances adjacent to vortical quadrupoles that are reminiscent of Taylor-Görtler flow structures in centrifugally unstable flows. Although the refractive-index fields obtained from axisymmetric simulations lead to smooth beam wavefronts, they are found to be unstable to azimuthal disturbances in three of the four three-dimensional cases considered. The azimuthal striations are optically detrimental, since they produce high-order angular aberrations that account for most of the beam wavefront error. A fourth case is computed at high input power and high induction frequency, which displays the best optical properties among all the three-dimensional simulations considered. In particular, the increase in induction frequency prevents local thermalization and leads to an axisymmetric distribution of electrons even after introduction of spatial disturbances. The results highlight the importance of accounting for spatial effects in the numerical computations when optical analyses of plasma lenses are pursued in this range of operating conditions.

• OSTI ID: 22494167
• Journal Information: Physics of Plasmas, Vol. 22, Issue 6; Other Information: (c) 2015 AIP Publishing LLC; 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
ARGON
AXIAL SYMMETRY
COMPUTERIZED SIMULATION
CYLINDRICAL CONFIGURATION
DISTURBANCES
ELECTRIC CURRENTS
ELECTRON DENSITY
ELECTRONS
HYDRODYNAMICS
PHASE VELOCITY
PHOTON BEAMS
PLASMA
QUADRUPOLES
RADIOWAVE RADIATION
REFRACTIVE INDEX
STAGNATION POINT
STRIATIONS
THERMALIZATION
THREE-DIMENSIONAL CALCULATIONS
VISIBLE RADIATION