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Abstract

A wide theoretical study on quasi-optical microwave propagation has been carried out in the range 3 GHz to 300 GHz. A high power TEMOO Gaussian beam can be propagated for long distances with low losses if a nearly-confocal system of mirrors is used as phase corrector. The theory of beam waveguides using elliptic parabolic reflectors has been critically revisited and developed. All the kind of losses (diffraction, matching, truncation, divergence, ohmic, atmospheric, depolarization, misalignment) have been examined in detail. Easy formulas and graphics are given to establish the influence of the different losses. Criteria to find the best design parameters of a quasi- optical transmission line are given once the frequency, the power and the available room are known. A practical scheme for the design of a Reflecting Beam Waveguide is reported in the Appendix. In general, a well designed Reflecting Beam Waveguide should permit the propagation of several MW in CW without a sensible beam shape deformation, and with total losses of about a fraction of % in 10 meters. Several examples at different frequencies are herein reported, and applications to high power Electron Cyclotron Heating and Lower Hybrid Heating of a plasma find a good solution using quasi-optical schemes. The comparison between Beam Waveguide systems and traditional oversized waveguides shows sensible advantages for the use of a quasi-optical propagation at higher frequencies. At low frequencies, the longer wavelengths permit high power capability also in waveguides; moreover the dimensions of the mirrors become rather important. Therefore at lower frequencies the choice of the best propagation system depends on contingent problems such as room availability. The wide bandwidth, the fact of having a single line needing no cooling and without requirements of high mechanical precision (as in certain waveguide components at high frequency), are other advantages of the Reflecting Beam Waveguide System (RBWS) which have been examined in this work.

Additional information

Authors: REBUFFI L CEA, DEPARTEMENT DE RECHERCHES SUR LA FUSION CONTROLEE, CEN, CADARACHE, SAINT-PAUL-LES-DURANCE, (FRANCE), CEA, DEPARTEMENT DE RECHERCHES SUR LA FUSION CONTROLEE, CEN, CADARACHE, SAINT-PAUL-LES-DURANCE, (FRANCE)
Bibliographic Reference: WRITE TO CEA MENTIONING REPORT EUR-CEA-FC-1327 EN, 1987
Availability: Can be ordered online
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