Phase Measurements of a 140-GHz Confocal Gyro-Amplifier
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Phase Measurements of a 140-GHz Confocal Gyro-Amplifier Guy Rosenzweig1,2 · Sudheer K. Jawla1 · Julian F. Picard1 Michael A. Shapiro1 · Richard J. Temkin1
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Received: 22 July 2020 / Accepted: 29 September 2020 / © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The phase stability of a 140-GHz, 1-kW pulsed gyro-amplifier system and the phase dependence on the cathode voltage were experimentally measured. To optimize the measurement precision, the amplifier was operated at 47 kV and 1 A, where the output power was ∼ 30 W. The phase was determined to be stable both pulseto-pulse and during each pulse, so far as the cathode voltage and electron beam current are constant. The phase variation with voltage was measured and found to be 130 ± 30◦ /kV, in excellent agreement with simulations. The electron gun used in this device is non-adiabatic, resulting in a steep slope of the beam pitch factor with respect to cathode voltage. This was discovered to be the dominant factor in the phase dependence on voltage. The use of an adiabatic electron gun is predicted to yield a significantly smaller phase sensitivity to voltage, and thus a more phase-stable performance. To our knowledge, these are the first phase measurements reported for a gyro-amplifier operating at a frequency above W-band. Keywords Gyro-amplifier · Gyrotron · Phase stability · Vacuum electronics · DNP-NMR
1 Introduction Phase stability of an amplifier is an important property for many applications. For example, one approach for improving dynamic nuclear polarization (DNP) efficiency of nuclear magnetic resonance (NMR) spectroscopy is the exchange of
Guy Rosenzweig
[email protected] 1
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2
Present address: MKS Instruments, Inc., Wilmington, MA 01887, USA
International Journal of Infrared and Millimeter Waves
continuous wave microwave irradiation for short, strong pulses as a means of increasing the bandwidth of a DNP experiment without increasing average power [1]. Gyro-amplifiers can produce the high power at high frequencies needed for pulsed DNP-NMR experiments [2, 3]. By sending a tailored train of short pulses into the gyro-amplifier, a high-power train can be generated for use in the spectrometer. Control over the phase of the microwaves could allow even broader bandwidths through manipulation of electron spins [4]. The input source is responsible for generating the pulses and controlling the phase, and it is important to verify that the relative phase between pulses is not altered during amplification. For this approach to be successful, the phase must be stable to within 10◦ . Other phase-sensitive applications include coherent radars, communication systems, accelerators, and linear colliders. The phase stability of gyro-amplifiers has been the subject of intensive theoretical and experimental research [5–15], but thus far it has only been measured up to W-band, for any amplifier. Existing techniques are challengi
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