Boller, K.-J.
(Klaus Boller)

MOPOS39 The Effect of Liner Induced Phase Fluctuations on the Gain of a Cerenkov FEL
Isabel de la Fuente, Klaus Boller, Peter van der Slot (UTWENTE, Enschede)

It is well known that wiggler errors can degrade the gain of a FEL. A similar process takes places in a Cerenkov FEL where the phase velocity of the amplified EM wave is determined by parameters of the dielectric liner. Thus deviations in the inner radius (Rd) of the liner will result in fluctuations of the phase velocity of the EM wave. E.g., for a quartz liner (εr=4.4) with Rd = 1.5 mm and outer radius of 4 mm, the derivative of the longitudinal wavenumber with respect to Rd is about 105 m-2 for a frequency of 50 GHz. Thus fluctuations in the Rd induce phase fluctuations that may degrade the gain of a Cerenkov FEL. In contrast to the undulator FEL, where the relative phase fluctuations are a result from deviations in the electron trajectories, the phase fluctuations are a result of pertubations in the radiation field for a Cerenkov FEL. As an example of the influence of pertubations in the inner radius of the liner on the gain we will present results of an analysis for a 100 kV Cerenkov FEL operating at a frequency of 50 GHz.

THPOS33 A mm-Wave, Table Top Cerenkov Free-Electron Laser
Isabel de la Fuente, Klaus Boller, Peter van der Slot (UTWENTE, Enschede)

We have designed and constructed a compact (0.5 x 1.5 m), 100 kV Cerenkov FEL operating at a frequency of 50 GHz. The electron beam is produced by a gridded thermionic electron gun with a beam current of 800 mA. Simulations shows that 800 mA is sufficient to produce an output power of ~ 1 kW peak at 50 GHz using a total cavity reflectivity of about 10 to 20 %. The average power approaches 1 kW when the electron pulse length is extended to CW. A depressed collector will be used to increase the overall efficiency of this device. Special attention has been given to the outcoupler that has to combine multiple functions. First it has to separate the radiation field from the electron beam. Second it has to be transparent for the electron beam and acts as a partial reflector for radiation. Finally it has to convert the generated TM01 mode in the interaction region into the fundamental TE01 mode of the standard rectangular output port. We will present the overall design and experimental set-up, first experimental results and discuss possible applications for this table-top Cerenkov FEL.