Free-electron masers based on two-dimensional distributed feedback

A.D.R. Phelps, I.V. Konoplev, A.W. Cross, Philip Macinnes, W. He, K. Ronald, C.G. Whyte, C.W. Robertson

Research output: Chapter in Book/Report/Conference proceedingChapter


The results of experimental studies of a coaxial free-electron masers (FEM) based on two-dimensional distributed feedback are presented. In the first set of experiments the FEM's interaction region was formed by a two-mirror cavity with 2D Bragg structures as input and output mirrors. In the second set of experiments a cavity with 2D and 1D mirrors was used. In both cases the input mirror provided two-dimensional (2D) distributed feedback and ensured mode selection over the wave azimuthal index, while the output mirror was used to close the feedback loop inside the two-mirror cavity. It was demonstrated that substituting the 2D output mirror with a 1D Bragg structure increased the output power while still maintaining spectral purity and spatial and temporal coherence. The FEM has been driven by an oversized high-current (1.5 kA) thin annular electron beam of 200 ns pulse duration. An maximum output power of ~60 MW corresponding to an efficiency of 10% was measured for an FEM based on 2D/1D cavity. The directional mode pattern of the microwave radiation from the output horn was also measured and compared with theoretical prediction. Analysing the spectrum of the RF signal the location of the operating frequency was found.
Original languageEnglish
Title of host publication IEEE International Vacuum Electronics Conference, 2007
Subtitle of host publicationIVEC '07
Place of PublicationPiscataway, New Jersey
Number of pages2
ISBN (Print)1-4244-0633-1
Publication statusPublished - May 2007

Publication series

NameInternational Vacuum Electronics Conference IVEC


  • Bragg gratings
  • electron beams
  • feedback
  • masers
  • mirrors
  • annular electron beam
  • coaxial free-electron masers
  • microwave radiation pattern
  • spatial coherence
  • spectral purity


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