A high-power Ka-band Free-Electron Maser, defined by a 2D – 1D Bragg lasing cavity

TL;DR: In this paper, the lasing cavity is defined using periodic corrugations on the drift-tube walls, whose reflection bands determine the dominant resonance of the maser, leading to monochromatic output at power levels of several tens of megawatts and pulse durations of ∼150ns (determined primarily by the pulse duration of the driving power supply of ∼250ns).

Abstract: Summary form only given. One of the on-going research programs, at the University of Strathclyde, involves the development of high-power, pulsed, Free-Electron Masers (FEMs) with the lasing cavity defined using periodic corrugations on the drift-tube walls1–4. These corrugations form 1D and 2D Bragg resonators, whose reflection bands determine the dominant resonance of the maser5. Proper selection of the FEM undulator magnetic field strength, allows for efficient extraction of energy from a mildly relativistic (400 – 500 keV) electron beam at the resonant frequency of the lasing cavity, leading to monochromatic output at power levels of several tens of megawatts and pulse durations of ∼150ns (determined primarily by the pulse duration of the driving power supply of ∼250ns).

Full text

A HIGH-POWER Ka-BAND FREE-ELECTRON
MASER, DEFINED BY A 2D – 1D BRAGG LASING
CAVITY
Philip MacInnes, Ivan V. Konoplev, Adrian W. Cross,
Wenlong He, Helen Yin, Colin G. Whyte, Craig W. Robertson,
Kevin Ronald and Alan D. R. Phelps.
SUPA Department of Physics, University of Strathclyde,
Glasgow, Lanarkshire, Scotland
One of the on-going research programs, at the University of
Strathclyde, involves the development of high-power, pulsed,
Free-Electron Masers (FEMs) with the lasing cavity defined
using periodic corrugations on the drift-tube walls
1-4
. These
corrugations form 1D and 2D Bragg resonators, whose
reflection bands determine the dominant resonance of the
maser
5
. Proper selection of the FEM undulator magnetic field
strength, allows for efficient extraction of energy from a
mildly relativistic (400 – 500 keV) electron beam at the
resonant frequency of the lasing cavity, leading to
monochromatic output at power levels of several tens of
megawatts and pulse durations of ~150ns (determined
primarily by the pulse duration of the driving power supply of
~250ns).
This paper presents the results from the current iteration of the
FEM experiment, which utilizes a 2D Bragg input mirror,
coupled with a 1D Bragg output mirror
4
. Single frequency
operation is demonstrated, as is a degree of tunability, via
variation in the undulator magnetic field strength. The
experimental results are compared with numerical and
analytical studies.
1. A. W. Cross et al., ”Experimental and theoretical study of
2D Bragg structures for a coaxial free electron maser”,
Nuclear Instruments and Methods in Physics Research A,
2001, pp. 164 – 172.
2. A. W. Cross et al., ”Experimental studies of coaxial two-
dimensional Bragg structures for a high power free electron
maser”, Applied Physics Letters, 8(9), 2002, pp. 1517 – 1519.
3. I. V. Konoplev et al., “Experimental and theoretical studies
of a free electron maser based on two-dimensional distributed
feedback”, Physical Review E, 76, 2007, article: 056406.
4. I. V. Konoplev et al., “High current electron Beams for
high power free electron masers based on two-dimensional
periodic lattices”, IEEE Transactions on Plasma Science,
38(4), 2010, pp. 751 – 763.
5. N. S. Ginsburg et al., ”mode competition and control in
free electron lasers with one and two dimensional Bragg
resonators”, Nuclear Instruments and Methods in Physics
Research A, 375, 1996, pp. 202 – 206.