On operation and control of CW magnetrons for superconducting accelerators

TL;DR

This paper reviews modeling and experimental techniques for controlling CW magnetrons, focusing on suppressing regenerative noise through forced RF oscillation to enable their use in superconducting accelerators.

Contribution

It introduces methods for controlling CW magnetrons with injected signals to reduce noise, facilitating their application in SRF accelerators.

Findings

PIC modeling of magnetron operation

Experimental validation of noise suppression techniques

Development of control strategies for stable magnetron operation

Abstract

CW magnetrons, developed for industrial RF heaters, were suggested to feed RF cavities of superconducting accelerators due to higher efficiency and lower cost of RF power than provide traditionally used klystrons, IOTs or solid-state amplifiers. RF amplifiers driven by a master oscillator serve as coherent RF sources. CW magnetrons are regenerative RF auto generators with a huge regenerative gain. This causes regenerative instability with a notable noise when a magnetron operates as an auto generator i.e., with the anode voltage above the threshold of self-excitation. Traditionally, an injection locking by a small signal is used for phase stabilization of magnetrons. In this case CW magnetrons with the injection-locked (coherent) oscillations generate a notable level of noise. This may preclude use of CW magnetrons in this mode in the Superconducting RF (SRF) accelerators. This paper reviews PIC modeling and previously obtained experimental results for the operation and control of CW magnetrons, which led to the development of techniques most suitable for various SRF accelerators using forced RF oscillation of magnetrons, when the magnetron is launched by an injected forcing signal, and regenerative noise is suppressed.