R.A. Stuart, C.C. Wright, A.I. Al-Shamma'a, J. Lucas
The University of Liverpool, Dept. of Elec. Eng. and Electronics, Brownlow Hill, Liverpool L69 3GJ, U.K.
A waveguide Free Electron Maser (FEM) operating in the X-band frequency range has been constructed. During examination of the effect of seeding on the radiation growth of this device, it has been observed that the frequency of a resonant mode varies slightly with acceleration voltage. It is proposed that this effect is due to a change in the refractive index of the cavity due to the voltage dependent variation in the phase of the radiation caused by the interaction with the electron beam. A comparison is made between the observed variation of frequency with voltage and calculations made using the small signal approximation.
