Broadband Amplification of Low-Terahertz Signals Using Axis-Encircling Electrons in a Helically Corrugated Interaction Region

Abstract

Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the (75-110)-GHz frequency band and based on a helically corrugated interaction region. The second harmonic cyclotron mode of a 55-keV, 1.5-A, axis-encircling electron beam is used to resonantly interact with a traveling TE_{21}-like eigenwave achieving broadband amplification. The gyro-TWA demonstrates a 3-dB gain bandwidth of at least 5.5 GHz in the experimental measurement with 9 GHz predicted for a wideband drive source with a measured unsaturated output power of 3.4 kW and gain of 36-38 dB. The approach may allow a gyro-TWA to operate at 1 THz.

Gridded Cusp Gun for a Terahertz Gyro-Amplifier

“…In the gyro-TWA, a helically corrugated waveguide is used as the interaction region, and a cusp electron gun is used to generate a large orbit axis-encircling electron beam. The design of the cusp electron gun for the high-frequency gyro-TWA was based on the previous experience of two guns for two W-band gyro-devices, a gyrotron backward wave oscillator (gyro-BWO) [1] and a gyro-TWA [2][3][4][5].…”

Microwave Undulator Using a Helically Corrugated Waveguide

“…It has interesting features as it can couple two operating modes in the circular waveguide to generate new eigenmodes. It has attracted considerable interest and found its applications in gyrotron backward wave oscillators (gyro-BWOs) [15,16], gyrotron traveling wave amplifiers (gyro-TWAs) [17][18][19], mode converters [20,21], microwave pulse compressors [22,23], and as a microwave undulator [11]. The inner surface of an HCW can be expressed in cylindrical coordinates as ( , ) = 0 + 1 ( + 2 / ) (5) where R 0 is the mean radius of the circular waveguide, R 1 is the corrugation depth, m B is the fold number, and d is the axial period of the corrugation.…”

Output coupler for a THz gyro-amplifier

“…Further enhancement to the gyro-TWA's naturally wide bandwidth can be made through changing its interaction region to a helically corrugated interaction region (HCIR) [1]. A gyro-TWA operating in the W-band frequency range, and based on a HCIR in conjunction with a cusp electron gun [2,3], was measured to have 3.4 kW output power over 91-96.5 GHz [4]. Further experiments have been conducted to demonstrate its frequency agility in amplifying a 1 GHz frequency-swept input signal [5].…”