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Title: Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering

Abstract

Lower hybrid waves are studied in the Princeton ACT-I steady-state toroidal plasma device using a radially scanning CO/sub 2/ laser scattering system with both amplitude and phase sensitive detection techniques. Clearly defined resonance cones launched from external electrostatic antennas are seen to disappear as the plasma density is raised. Scaling of LHW laser signal with RF power in the presence of resonance cones shows nonlinearities associated with RF induced changes in the effective laser scattering volume. Absolute fluctuation level estimates suggest this occurs when e PHI/T/sub e/ greater than or equal to 1. Wavefront curvature effects can cause a complete loss of resonance cone laser signals, even though probes indicate that cones are still present. Measurements of the wave k/sub perpendicular/-spectrum in the plasma show direct evidence for electron Landau filtering of the original wave k/sub parallel/-spectrum launched from the antenna at the plasma edge, and strong dependence on antenna phasing. Finally, frequency shifts and loss of the resonance cone signal are associated with high levels of plasma density edge turbulence.

Authors:
; ;
Publication Date:
Research Org.:
Princeton Univ., NJ (USA). Plasma Physics Lab.
OSTI Identifier:
6845525
Alternate Identifier(s):
OSTI ID: 6845525; Legacy ID: DE84013098
Report Number(s):
PPPL-2101
ON: DE84013098
Resource Type:
Technical Report
Resource Relation:
Other Information: Portions are illegible in microfiche products. Original copy available until stock is exhausted
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; LOWER HYBRID HEATING; MONITORING; TOKAMAK DEVICES; ANTENNAS; CARBON DIOXIDE LASERS; LASER RADIATION; NONLINEAR PROBLEMS; PLASMA WAVES; CLOSED PLASMA DEVICES; ELECTRICAL EQUIPMENT; ELECTROMAGNETIC RADIATION; EQUIPMENT; GAS LASERS; HEATING; HIGH-FREQUENCY HEATING; LASERS; PLASMA HEATING; RADIATIONS; THERMONUCLEAR DEVICES 700205* -- Fusion Power Plant Technology-- Fuel, Heating, & Injection Systems

Citation Formats

Wurden, G.A., Wong, K.L., and Ono, M. Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering. United States: N. p., 1984. Web. doi:10.2172/6845525.
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Wurden, G.A., Wong, K.L., & Ono, M. Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering. United States. doi:10.2172/6845525.
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Wurden, G.A., Wong, K.L., and Ono, M. Sun . "Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering". United States. doi:10.2172/6845525. https://www.osti.gov/servlets/purl/6845525.
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@article{osti_6845525,
title = {Lower hybrid wave resonance cone detection via CO/sub 2/ laser scattering},
author = {Wurden, G.A. and Wong, K.L. and Ono, M.},
abstractNote = {Lower hybrid waves are studied in the Princeton ACT-I steady-state toroidal plasma device using a radially scanning CO/sub 2/ laser scattering system with both amplitude and phase sensitive detection techniques. Clearly defined resonance cones launched from external electrostatic antennas are seen to disappear as the plasma density is raised. Scaling of LHW laser signal with RF power in the presence of resonance cones shows nonlinearities associated with RF induced changes in the effective laser scattering volume. Absolute fluctuation level estimates suggest this occurs when e PHI/T/sub e/ greater than or equal to 1. Wavefront curvature effects can cause a complete loss of resonance cone laser signals, even though probes indicate that cones are still present. Measurements of the wave k/sub perpendicular/-spectrum in the plasma show direct evidence for electron Landau filtering of the original wave k/sub parallel/-spectrum launched from the antenna at the plasma edge, and strong dependence on antenna phasing. Finally, frequency shifts and loss of the resonance cone signal are associated with high levels of plasma density edge turbulence.},
doi = {10.2172/6845525},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EST 1984},
month = {Sun Apr 01 00:00:00 EST 1984}
}
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Technical Report:
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DOI:  10.2172/6845525
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  • ; ; - Phys. Fluids; (United States)
    Lower-hybrid waves are studied in the Princeton ACT-I steady-state toroidal plasma device using a radially scanning CO/sub 2/ laser scattering system with both amplitude and phase sensitive detection techniques. Clearly defined resonance cones launched from external electrostatic antennas are seen to disappear as the plasma density is raised. Scaling of a lower-hybrid wave (LHW) laser signal with radio-frequency (RF) power in the presence of resonance cones shows nonlinearities associated with RF-induced changes in the effective laser scattering volume. Absolute fluctuation level estimates suggest that this occurs when ePhi/T/sub e/> or =1. Wave-front curvature effects can cause a complete loss ofmore » resonance cone laser signals, even though probes indicate that cones are still present. Measurements of the wave k/sub perpendicular/ spectrum in the plasma show direct evidence for electron Landau filtering of the original wave k/sub parallel/ spectrum launched from the antenna at the plasma edge, and strong dependence on antenna phasing. Finally, frequency shifts and loss of the resonance cone signal are associated with high levels of plasma density edge turbulence.« less

  • ; - Phys. Rev. A; (United States)
    Results are given of a CO/sub 2/-laser scattering experiment on lower-hybrid waves at a frequency of 2.45 GHz performed in the Frascati tokamak. Signals are found in the location predicted by a ray-tracing code. The N/sub X/ spectrum (N/sub X/ = (c/..omega..) x K/sub X/, where K/sub X/ is the component of the wave vector in the magnetic field direction and ..omega../2..pi.. is the wave frequency) of lower-hybrid waves is determined at the plasma center showing a depletion of the high-N/sub X/ with respect to the launched spectrum in the scattering volume.

  • To measure and classify the Post-Rosenbluth convective loss-cone instability in MFTF, we propose to use a CO/sub 2/ laser consisting of a TEA-pulsed section and a low pressure CW section, together with a light mixing receiver. Calculations show that this system offers sufficient power and sensitivity to detect instability throughout the range from strong coherent light scattering to weak incoherent scattering when the instability is eliminated.

  • ; ;
    It is shown that the alpha particle contribution to the scattered power can be dominant in the coherent scattering of CO/sub 2/ laser in a Maxwellian plasma. The optimal forward scattering angle is around 1.0/sup 0/ with detection of the electron density fluctuation wavenumbers k/sub perpendicular to/ >> k/sub parallel/ (relative to the toroidal magnetic field). Because of the strong dependence of the scattered signal on the alpha particle temperature and the alpha distribution function, it seems feasible that CO/sub 2/ laser scattering, with clever heterodyne techniques, could give detailed local information on fusion alphas.

  • ;
    Experimental measurements show that coherent, azimuthal density fluctuations (1) focus lower hybrid resonance cones azimuthally, and (2) modulate the radial location of the resonance cones. A simple theory based on wave refraction is presented; this theory is in good agreement with the experimental observations. The theory is extended to give a physical description of wave propagation through turbulent, isotropic (perpendicular to B) noise such as has been observed in tokamaks; it is found that the turbulence causes the lower hybrid wave-vectors to have an angular spread in the plane perpendicular to B.