Theoretical investigation of an advanced launcher for a 2-MW 170-GHz TE/sub 34,19/ coaxial cavity gyrotron

This paper investigates the antenna waveguide (launcher), the main component of the quasi-optical mode converter of a 2-MW 170-GHz TE/sub 34,19/ coaxial cavity gyrotron, which is under development within the European Union. For coaxial gyrotrons operating in very high-order cavity modes like the TE/sub 34,19/, due to the ratio of the caustic to cavity radius of 0.323, the transformation of the high-order cavity mode into a nearly Gaussian distribution cannot be done as good as for gyrotron modes where the ratio of caustic to cavity radius is approximately 0.5. The simulation results for the TE/sub 34,19/ mode show that the average and peak values of the power density at the edges of the cuts of a conventional dimpled-wall launcher are approximately 32.3 W/cm/sup 2/ and 63.8, respectively, which will produce diffraction losses and reflection of power from the cuts. This paper reports on an advanced launcher for which average and peak values of power density of 1.9 and 5.4 W/cm/sup 2/ at the edges of the cuts are achieved, and a well-focused field at the aperture with a scalar Gaussian mode content of 94.8% is obtained.

[1]  M. Thumm,et al.  Gyrotron output launchers and output tapers , 1993 .

[2]  Jianbo Jin,et al.  Quasi-Optical Mode Converter/Mirror System for a High-Power Coaxial-Cavity Gyrotron , 2006, IEEE Transactions on Plasma Science.

[3]  G. G. Denisov,et al.  Asymptotic Theory of High-Efficiency Converters of Higher-Order Waveguide Modes into Eigenwaves of Open Mirror Lines , 2004 .

[4]  G. Dammertz,et al.  A 2-MW, 170-GHz coaxial cavity gyrotron , 2004, IEEE Transactions on Plasma Science.

[5]  T. Rzesnicki,et al.  The design of a quasi-optical mode converter for a coaxial-cavity gyrotron , 2004, Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004..

[6]  M. I. Petelin,et al.  Transformation of a whispering gallery mode, propagating in a circular waveguide, into a beam of waves , 1975 .

[7]  G. Gantenbein,et al.  Development of a 140 GHz, 1 MW, Continuous Wave Gyrotron for the W7-X Stellarator , 2001 .

[8]  G. G. Denisov,et al.  110 GHz gyrotron with a built-in high-efficiency converter , 1992 .

[9]  J. L. Hirshfield,et al.  Generation and Application of High Power Microwaves , 1998 .

[10]  J. Neilson,et al.  Surf3d and LOT : computer codes for design and analysis of high-performance QO launchers in gyrotrons , 2004, Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004..

[11]  A. Chirkov,et al.  Concepts and present status for multi-mode quasi-optical converters in gyrotrons , 2004, Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004..

[12]  Y. Hirata,et al.  The design of a tapered dimple-type mode converter/launcher for high-power gyrotrons , 2003 .

[13]  J. Doane.  Propagation and mode coupling in corrugated and smooth-wall circular waveguides , 1985 .

[14]  Richard J. Temkin,et al.  Theoretical and experimental investigation of a quasi-optical mode converter for a 110-GHz gyrotron , 1996 .

[15]  S. N. Vlasov,et al.  Quasioptical transformer which transforms the waves in a waveguide having a circular cross section into a highly directional wave beam , 1974 .