[en] The first multimegawatt harmonic relativistic gyrotron traveling-wave tube (gyro-twt) amplifier experiment has been designed, built, and tested. Results from this experimental setup, including the first ever reported third-harmonic gyro-twt results, are presented. Operation frequency is 17.1 GHz. Detailed phase measurements are also presented. The electron beam source is SNOMAD-II, a solid-state nonlinear magnetic accelerator driver with nominal parameters of 400 kV and 350 A. The flat-top pulsewidth is 30 ns. The electron beam is focused using a Pierce geometry and then imparted with transverse momentum using a bifilar helical wiggler magnet. Experimental operation involving both a second-harmonic interaction with the TE₂₁ mode and a third-harmonic interaction with the TE₃₁ mode, both at 17 GHz, has been characterized. The third-harmonic interaction resulted in 4-MW output power and 50-dB single-pass gain, with an efficiency of up to ∼8%. The best measured phase stability of the TE₃₁ amplified pulse was ±10 degree over a 9-ns period. The phase stability was limited because the maximum RF power was attained when operating far from wiggler resonance. The second harmonic, TE₂₁ had a peak amplified power of 2 MW corresponding to 40-dB single-pass gain and 4% efficiency. The second-harmonic interaction showed stronger superradiant emission than the third-harmonic interaction. Characterizations of the second- and third-harmonic gyro-twt experiments presented here include measurement of far-field radiation patterns, gain and phase versus interaction length, phase stability, and output power versus input power

[en] Cyclotron resonance maser amplifiers are possible sources for applications such as electron cyclotron resonance heating of fusion plasmas and driving high-gradient rf linear accelerators. For accelerator drivers, amplifiers or phase locked-oscillators are required. A 17 GHz cyclotron autoresonance maser (CARM) amplifier experiment and a 17 GHz third harmonic gyro-amplifier experiment are presently underway at the MIT Plasma Fusion Center. Using the SRL/MIT SNOMAD II induction accelerator to provide a 380 kV, 180 A, 30 ns flattop electron beam, the gyro-amplifier experiment has produced 5 MW of rf power with over 50 dB of gain at 17 GHz. The gyro-amplifier operates in the TE₃₁ mode using a third harmonic interaction. Because of its high power output, the gyro-amplifier will be used as the rf source for a photocathode rf electron gun experiment also taking place at MIT. Preliminary gyro-amplifier results are presented, including measurement of rf power, gain versus interaction length, and the far-field pattern. A CARM experiment designed to operate in the TE₁₁ mode is also discussed

[en] CARMs are attractive sources for applications such as electron cyclotron resonance heating of fusion plasmas and driving high-gradient RF linear accelerators. For applications such as accelerator drivers, amplifiers or locked-oscillators are required. A 17 GHz cyclotron autoresonance maser (CARM) amplifier experiment is presently underway at the MIT Plasma Fusion Center. This experiment uses an electron beam generated by the 500 kV injector on the SRL/MIT SNO-MAD II induction accelerator. The present gun geometry produces a beam at 400 kV in a 50 ns pulse. The amplifier is designed to operate in the TE₁₁ mode. To date, only second and third harmonic relativistic gyro-TWT modes have been seen. The power levels of these modes are ∼ 1 MW. The authors characterize these modes and discuss steps which they are taking in order to operate in the TE₁₁ CARM mode. A high power, 17 GHz CARM amplifier has numerous applications. An RF injection electron gun is currently being designed at MIT that has RF input requirements quite comparable to the CARM amplifier's predicted rf output. A potential high degree of phase stability may allow the CARM amplifier to serve as a driver for future high gradient linear e⁺e^- colliders

[en] Experimental results on a long pulse, high frequency, cyclotron autoresonance maser oscillator (CARM) are reported. An electron gun produces a 1 μs, 450 kV, 80 A electron beam with good beam quality. A bifilar magnetic wiggler operated near the guide field resonance followed by an adiabatic compression of the guide field is used to impart transverse velocity (β perpendicular) to the beam. A capacitive probe, located after the adiabatic compression, is used to measure the mean parallel velocity of the beam, and using energy conservation the beam pitch (α = β perpendicular/β parallel) is derived. The measured α values are significantly higher than the theoretical values. The interaction region is defined by a Bragg resonator designed to oscillate in the TE₁₁ mode at 27.8 GHz (diffractive quality factor Q_D = 300). A cold test measurement of the resonant frequency of the Bragg resonator is consistent with the designed frequency. A rf power level of 1.9 MW (5.2% efficiency) has been measured in the TE₁₁ mode at the designed frequency; however, significant mode competition is observed between TE₁₁ mode and TM₀₁ mode. Identification of these CARM modes is made by comparison of measured frequencies with cold test frequencies, uncoupled dispersion theory and measurement of the far field radiation pattern. Operation in the TE₁₁ CARM mode occurred at a Doppler upshifted frequency of 2.9 times the relativistic cyclotron frequency

[en] In this paper high-power CARM and FEL research on a long-pulse (1 μs) high-voltage (700 kV) modulator at the MIT Plasma Fusion Center is described. The experimental results on a Ka-band, long-pulse CARM oscillator experiment are presented. In this experiment, a SLAC 5045 klystron gun produced an electron beam at 250-320 kV and 10-20 A; a beam α ≡ p perpendicular/p parallel, variable from 0 to 1, was produced on this electron beam with a wiggler magnetic field near guide field resonance. CARM operation was observed for many parameter settings, and for frequencies ranging from 29 to 32 GHz. Output powers as high as 110 kW were achieved with an efficiency of up to 1.8%. Higher frequency radiation at 74.5 GHz was also obtained and is attributed to second harmonic CARM operation. Recent operation of an FEL experiment using a 580 kV, 0.27 μP electron gun, built by Thomson Tubes Electroniques, and a permanent magnet helical wiggler with λ_w ± 3 cm and B_w = 500 G is described. Results include measurement of small signal gain, gain-bandwidth, and oscillation at 30 GHz, with power levels of approximately 1 MW

[en] Cyclotron autoresonance maser (CARM) amplifiers are under investigation as a possible source of high-power (> 100 MW), high-frequency (> 10 GHz) microwaves for powering the next generation of linear colliders. A design for a high-power, short pulse, 17.136 GHz CARM amplifier, utilizing a 500 kV linear induction accelerator, is presented

[en] Cyclotron resonance maser amplifiers are possible sources for applications such as electron cyclotron resonance heating of fusion plasmas and driving high-gradient rf linear accelerators. For accelerator drivers, amplifiers or phase locked-oscillators are required. A 17 GHz cyclotron autoresonance maser (CARM) amplifier experiment and a 17 GHz third harmonic gyro-amplifier experiment are presently underway at the MIT Plasma Fusion Center. Using the SRL/MIT SNOMAD II introduction accelerator to provide a 380 kV, 180 A, 30 ns flat top electron beam, the gyro-amplifier experiment has produced 5 MW of rf power with over 50 dB of gain at 17 GHz. The gyro-amplifier operates in the TE₃₁ mode using a third harmonic interaction. Because of its high power output, the gyro-amplifier will be used as the rf source for a photocathode rf electron gun experiment also taking place at MIT. Preliminary gyro-amplifier results are presented, including measurement of rf power, gain versus interaction length, and the far-field pattern. A CARM experiment designed to operate in the TE₁₁ mode is also discussed