Tunable 35-200GHz gyrotron

S. N. Spark

doi:10.1117/12.2301636

1 December 1990 Tunable 35-200GHz gyrotron

S. N. Spark

Proceedings Volume 1514, 15th International Conference on Infrared and Millimeter Waves; 15146A (1990) https://doi.org/10.1117/12.2301636
Event: 15th International Conference on Infrared and Millimeter Waves, 1990, Orlando, FL, United States

Abstract

The extended frequency tuning range of the Strathclyde University gyrotron will be demonstrated. The gyrotron consisted of a field-immersed, field emission cold cathode and a shaped anode cavity. The cavity was oversized with an ill-defined boundary at one end. This system could therefore support the oscillation of a very large number of TE_pqs modes. The maser was thus highly tunable via differential mode excitation. A heterodyne technique was used to demonstrate the maser oscillation in the Ka-band (26.5-40GHz) , with the maser oscillating at 35GHz in the TE₀₁ mode. Previous to this, a quasi-optical diffraction grating spectrometer was used to show the maser was oscillating under different conditions respectively, single and multi-mode in the W-band (75-110GHz) and multimode in the G-band(140-220GHz). To control the output beam a quasioptical mode converter has been successfully developed. This converts various TE_pq modes into a Gaussian beam. Studying the output of the maser, the mm-wave pulse has been shown to consist of a -100ns envelope containing -2ns pulses spaced -5ns apart. Although this behaviour may have several explanations, some of the most recent code simulations predict this behaviour as a result of mode beating in the complex transient start-up of the maser oscillation. With this gyrotron supporting not only many transverse modes but also several longitudinal modes, such beating is a likely consequence.

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S. N. Spark "Tunable 35-200GHz gyrotron", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15146A (1 December 1990); https://doi.org/10.1117/12.2301636

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KEYWORDS

Electron beams

Gaussian beams

Collimation

Diffraction gratings

Heterodyning

Ka band

Spectroscopy

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