Precision vector control of a superconducting RF cavity driven by an injection locked magnetron

Abstract

-The insulating vacuum system of the SNS cryomodules P Ladd, X Geng, M C Hammons et al. -Upgrade of the cryogenic infrastructure of SM18, CERN main test facility for superconducting magnets and RF cavities A Perin, F Dhalla, P Gayet et al. E-mail: chase@fnal.govABSTRACT: The technique presented in this paper enables the regulation of both radio frequency amplitude and phase in narrow band devices such as a Superconducting RF (SRF) cavity driven by constant power output devices i.e. magnetrons [1]. The ability to use low cost high efficiency magnetrons for accelerator RF power systems, with tight vector regulation, presents a substantial cost savings in both construction and operating costs -compared to current RF power system technology. An operating CW system at 2.45 GHz has been experimentally developed. Vector control of an injection locked magnetron has been extensively tested and characterized with a SRF cavity as the load. Amplitude dynamic range of 30 dB, amplitude stability of 0.3% r.m.s, and phase stability of 0.26 degrees r.m.s. has been demonstrated.

Resonant interaction of the electron beam with a synchronous wave in controlled magnetrons for high-current superconducting accelerators

“…Capabilities of the injection-locked magnetrons for the listed methods of phase and power control have been verified in experiments with 2.45 GHz, CW, 1 kW magnetrons; see Refs. [13][14][15]. The behavior of magnetrons in the experiments was in accordance with the developed analytic model characterizing the phase grouping and the resonant interaction of the electrons with the synchronous wave in magnetrons.…”

“…The vector method of managing the depth of the phase modulation to control the magnetron power was tested by a single-cell 2.45 GHz SRF cavity with a loaded Q-factor Q L ≈ 2 × 10 7 , powered by the single CW magnetron type 2M137-IL. The measured rms phase and amplitude deviations of the accelerating field in the cavity at 4K did not exceed 0.26°and 0.3%, respectively, at a closed feedback-loop bandwidth of ∼100 kHz [14]. For 650 MHz SRF cavities with R=Q ¼ 610 Ohms the loaded Q-factor, Q L ≈ 2 × 10 7 corresponds to an accelerated current of ∼0.5 mA.…”

“…If the frequency of the depth modulation is much larger than the accelerating field bandwidth, the power concentrated in the sidebands is reflected from the cavity towards a dummy load. Thus, changes of the modulation depth result in a power change at the fundamental frequency [14]. The rf sources intended for powering SRF cavities for both vector methods operate at nominal power and a part of the power is continuously redistributed into a dummy load for absorption.…”

An efficient magnetron transmitter for superconducting accelerators

“…The second method requires only a single-channel magnetron transmitter, [5]. The phase-modulated injectionlocking signal provided a fast phase control.…”

“…Traces C and D are average efficiency of the 1.2 kW magnetron, at the extended current control,[6]. Trace E is the average efficiency of 1 kW magnetrons at power combining,[4], or at management of the depth of phase modulation,[5].…”