Effect of waveguide boundary conditions on the backscatter of lower hybrid waves

Schuss, J.J.

doi:10.1088/0029-5515/20/4/007

Cited by 4 publications

(3 citation statements)

References 12 publications

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“…Since this decay would occur at the plasma periphery where the waves are always accessible even for no < 1.5, it would produce phase-independent heating. Furthermore, it has been shown that such a decay occurring sufficiently close to the waveguide mouth would result in a wave power spectrum peaked at nn ~ c/o)(ir/b) ~ 5 where b is the waveguide width [35]. This decay would produce a frequency-downshifted lower-hybrid-wave spectrum, which is also experimentally observed in addition to the enhanced low-frequency wave spec-trum.…”

Section: Anomalous Heatingmentioning

confidence: 90%

“…Finally, this theory neglects any backscatter caused by turbulence or parametric instabilities of the lowerhybrid-wave power into the waveguide mouth. It has been predicted that any such backscatter will tend to bounce off the waveguide with a reflected n z power spectrum peaked at multiples of (c/w)(7r/b) [35], or for Alcator A parameters having a peak at n z ~ 5. This effect would, however, depend on the backscattering occurring close enough to the waveguide mouth so that the backscattered lower hybrid waves impinge on the waveguides.…”

Section: Figure Lb Plots P(n Z ) Andmentioning

confidence: 99%

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Lower hybrid heating in the Alcator A tokamak

et al. 1981

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The results and interpretation of the modest nower ( 90 kW) lower hybrid heating experiment on Alcator A are presented.The expected results from linear waveguide-plasma coupling theory are outlined, and the possible effects of parametric instabilities, scattering from density fluctuations, and imperfect energetic ion confinement are addressed.It is found experimentally that good coupling and the absence of rf breakdown are achieved with a double wavecuide array 2 at available rf power densities Prf < 2.5 kW/cm , the waveguide vacuum windows being outside the toroidal field magnets; a waveguide array having vacuum windows near the waveguide mouth so that the w = wc. layer can be pressurizedshows no breakdown at P > 8 kW/cm2 when a single waveguide is energized. Energetic ion wroduction and a factor of 50 increase in the :usion neutron rate are ozserved to take place at well defined values of central plasma density; below these densities electron heating occurs. The ion tail production is found to be independent of the relative phase of the double waveguide array employed. This ion heating occurs at a lower density than theoretically expected; together with the electron heating this indicates waves having n 1 5 being absorbed near the plasma center. Probes at the plasma edge observe a frequency downshifted and broadened rf pump signal that .is strongly attenuated as the plasma density increases through the neutron production band. These anomalous heating results and probe signals can be explained by a parametric decay of the pump wave into higher n lower hybrid waves near the plasma edge. An alternate qualitative explanation would be the poloidal scattering of the lower hybrid waves at the plasma periphery due to density fluctuations; the n,, of the scattered lower hybrid waves would then increase as they propagated inward due to magnetic shear. The neutron rate decay times imply that the rf creates ion tails having a substantial fraction of their energy above 50 keV.The neutron decay times and rates strongly depend on plasma current and indicate the expected influence of ion confinement on rf heating efficiencies. Finally the rf heating efficiencies are assessed.2

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Section: Anomalous Heatingmentioning

confidence: 90%

Section: Figure Lb Plots P(n Z ) Andmentioning

confidence: 99%

Lower hybrid heating in the Alcator A tokamak

et al. 1981

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“…D'yachenko and Shcherbinin [7] have investigated the excitation of slow waves by a wall near the plasma edge containing rectangular corrugations. The effect of a similar wall on the coupling of a waveguide array has been reported by Shcherbinin and Schuss [8][9]. In the first part of this paper, we calculate the mode structure that can be supported by a passive slow-wave structure consisting of a metal wall with sinusoidal corrugations, and investigate the coupling to slow plasma waves and dissipation of surface energy.…”

Section: Introductionmentioning

confidence: 65%

Propagation and reflection of slow plasma waves with a periodic metal boundary

Paoloni

1980

Nucl. Fusion

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The effects of a sinusoidally corrugated boundary on the generation and propagation of slow plasma waves are studied. The intention is to seek a method of minimizing surface wave energy in lower-hybrid-heating schemes. Firstly, an analysis is presented of the mode structure that can be supported by a periodic boundary. Significant coupling to slow plasma waves can occur for a wide range of conditions and penetration of waves into the plasma leads to dissipation of the surface fields. Secondly, the reflection of waves propagating from the interior of the plasma onto the boundary is considered. The presence of the corrugated wall modifies the parallel refractive index of the reflected wave components and, for particular geometrical conditions, leads to complete backscattering of the incident energy.

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Coherent centres for light amplification in coupled waveguide arrays

Tripathi

Kumar

2018

Optics Communications

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Effect of waveguide boundary conditions on the backscatter of lower hybrid waves

Cited by 4 publications

References 12 publications

Lower hybrid heating in the Alcator A tokamak

Lower hybrid heating in the Alcator A tokamak

Propagation and reflection of slow plasma waves with a periodic metal boundary

Coherent centres for light amplification in coupled waveguide arrays

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