Abstract
The harmonic operation in a terahertz gyrotron traveling-wave amplifier (gyro-TWA) permits a reduced magnetic field, whereas a harmonic multiplying gyro-TWA enables magnetic field reduction and frequency multiplication. This study comparatively analyzes the 400-GHz fourth-harmonic gyro-TWAs and fourth-harmonic multiplying gyro-TWAs with axis-encircling electron beams. This property of the gyro-TWAs with axis-encircling electron beams enables us avoid the appearance of the majority of the competing modes. According to the simulation results obtained using multi-mode codes, the attenuating severs suppress the remaining competing modes. In the case of a harmonic gyro-TWA containing a sever section, the copper-section start-oscillation length is significantly influenced by a decrease in the sever-section radius when compared with an increase in the sever-section length. Furthermore, a stable fourth-harmonic TE41-mode gyro-TWA containing sever sections is proposed. We propose fourth-harmonic TE41-mode multiplying gyro-TWAs, where the drive stages operate in the fundamental-harmonic TE11 mode to reduce the frequency of the drive wave. We subsequently develop a stable fourth-harmonic multiplying gyro-TWA with sever sections in the drive and amplified stages to avoid the competing modes and enhance the output power. The stable high-gain fourth-harmonic gyro-TWA can yield a peak output power of 2.7 kW at 400.6 GHz with a saturated gain of 75 dB and a bandwidth of 0.7 GHz for a 75-kV and 2-A electron beam with an axial velocity spread of 3%. Furthermore, a peak output power of 1.7 kW can be obtained by the fourth-harmonic multiplying gyro-TWA at 400.4 GHz with a saturated gain of 57 dB and a bandwidth of 0.4 GHz. Subsequently, we calculate the power and gain scaling for the harmonic gyro-TWA and harmonic multiplying gyro-TWA.
Highlights
The growing application of nuclear magnetic resonance, dynamic nuclear polarization, electron spin resonance, and deep space research has enabled the growth of terahertz-frequency gyrotrons.[1,2,3,4,5] Some conventional linear-beam devices, including backward wave oscillators, are available in the terahertz (THz) regime.[6]
The magnetic field of a gyrotron, which operates at the sth cyclotron harmonic, is almost 1/s of that of a gyrotron that operates at the fundamental cyclotron harmonic to reduce the magnetic field requirement associated with a THz gyrotron.[1]
The simulated results showed that the output power (Pout) at the output frequency of 400.7 GHz in the fourthharmonic gyro-TWA [Fig. 1(c)] was found to be proportional to the drive power corresponding to the linear gain of approximately 83 dB
Summary
The growing application of nuclear magnetic resonance, dynamic nuclear polarization, electron spin resonance, and deep space research has enabled the growth of terahertz-frequency gyrotrons.[1,2,3,4,5] Some conventional linear-beam devices, including backward wave oscillators, are available in the terahertz (THz) regime.[6]. Scitation.org/journal/adv output power of 90 kW in an amplifier with a saturated power bandwidth of 4 GHz.[10] A photonic bandgap interaction circuit is used to ensure stability from oscillations; a THz gyrotron amplifier has achieved a peak small-signal gain of 38 dB and an output power of 45 W at 247.7 GHz with a 3-dB bandwidth of 0.4 GHz.[11] A W-band gyro-TWA with a helically corrugated interaction region achieved an output power of ∼3 kW and a 3-dB gain bandwidth of minimum 5.5 GHz to achieve a wide amplification bandwidth.[12] the THz gyro-TWAs operating at a frequency of >400 GHz and achieving an output power of >1 kW have not been rapidly adopted because the maximum power of a solidstate driver is only 0.1 mW at 400 GHz.[13]
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