Abstract
The gyrotron travelling wave tube amplifiers (gyro-TWAs) presented in this paper can operate with high efficiency (30%), huge powers and wide bandwidths at high frequencies that no other amplifier can provide. In principle, this is a technology that can be scaled to >1 THz and operate with 20% bandwidths. Resonant coupling of two dispersive waveguide modes in a helically corrugated interaction region (HCIR) can give rise to a non-dispersive eigenwave over a wide frequency band. The synchronism between the ideal wave and an electron cyclotron mode, either fundamental or harmonic, of a large orbit electron beam contributes to the broadband amplification. An electron beam of 55 keV, 1.5 A with a velocity pitch angle of ~1 generated by a thermionic cusp gun is used in our 100 GHz gyro-TWA experiment, which achieves an unsaturated output power of 3.4 kW and gain of 36–38 dB. The design and experimental results of the many components making the gyro-TWA will be presented individually and then the whole system will be introduced. The amplification of a swept signal by the W-band gyro-TWA is demonstrated showing its capabilities in the field of telecommunications. Furthermore, the design studies of a cusp electron gun in the triode configuration and the realization of a 3-fold HCIR operating at 372 GHz will also be displayed.
Highlights
Generations of high-power sub-millimeter and terahertz (THz) radiation have drawn great interest in the last few decades due to their wide applications, such as communications, remote sensing, plasma heating, electron spin resonance, dynamic nuclear polarization-enhanced nuclear magnetic resonance, and others
Devices are based on the cyclotron resonance maser (CRM) instability [1] and they have a fast wave interaction
The gyrating electron beam is required to have large energy and a low spread in the transverse-to-axial velocity ratio, which makes it unattractive to be used in the gyro-TWAs interaction circuit
Summary
Generations of high-power sub-millimeter and terahertz (THz) radiation have drawn great interest in the last few decades due to their wide applications, such as communications, remote sensing, plasma heating, electron spin resonance, dynamic nuclear polarization-enhanced nuclear magnetic resonance, and others. The gyrating electron beam is required to have large energy and a low spread in the transverse-to-axial velocity ratio (pitch alpha), which makes it unattractive to be used in the gyro-TWAs interaction circuit. The large-orbit beam has the advantage of mode selection to reduce the mode competition, which allows the gyro-TWA to operate at the second harmonic of the cyclotron frequency, as required by the chosen interaction region. This allows a reduction in the required magnetic field strength by a factor of 2. A THz gyroTWA has been developed and its progress is introduced in the last section of this paper
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