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

W. He, C. R. Donaldson, L. Zhang, K. Ronald, A. D. R. Phelps, and A. W. Cross

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.184801

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 ${\mathrm{TE}}_{21}$-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.

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Abstract-Broadband amplification of low-terahertz signals using axis-encircling electrons in a helically corrugated interaction region

W. He, C. R. Donaldson, L. Zhang, K. Ronald, A. D. R. Phelps,  A. W. Cross,

https://journals.aps.org/prl/accepted/aa075Y48Q3c13a6851270ff5428f8a399615110c3


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 (HCIR). The second harmonic cyclotron mode of a 55 keV, 1.2 A, axis-encircling electron beam generated from a cusp electron gun was used to resonantly interact with a traveling TE21-like eigenwave, existing in the HCIR, achieving broadband amplification based on the cyclotron resonance maser instability. The gyro-TWA was measured to generate a maximum power of 3.4 kW with an unsaturated gain of 36-38 dB in the driving frequency band of 91-96.5 GHz.

Abstract-Simulation of rectangular TE10 to circular TE11 terahertz mode converters

J. R. Garner,   L. Zhang,  C. R. Donaldson,  A. W. Cross,  A. D. R. Phelps,  W. He,

http://ieeexplore.ieee.org/document/7758520/

Two designs of fundamental mode rectangular to circular waveguide TE10 to TE11 mode converter are presented. The waveguide transitions are optimized for operation as an input coupler on a 372 GHz gyro-TWA for Dynamic Nuclear Polarization (DNP) enhancement of NMR imaging. A T-junction input coupler and a multiple hole directional coupler were optimized for operation between 360-384 GHz. The T-junction coupler and the multiple hole coupler exhibited bandwidths of 10% and 35% respectively with a high coupling factor of > -1 dB.

Abstract-High power wideband gyrotron backward wave oscillator operating towards the terahertz region

W. He, C. R. Donaldson, L. Zhang, K. Ronald, P. McElhinney, and A. W. Cross
http://prl.aps.org/accepted/fa07cYcdM9c12133c6286d9809d8d09987fde325b
Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low terahertz region. A helically corrugated interaction region (HCIR) was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell (PIC) numerical simulations