Abstract
We have used coherent Smith-Purcell radiation in order to investigate the longitudinal (temporal) profile of the electron bunch at the FELIX facility. Detection of the far-infrared radiation was achieved by a simple and compact experimental arrangement, consisting of an array of 11 room-temperature pyroelectric detectors. Accurate determination of the background radiation, use of high quality optical filters, and an efficient light collection system are essential for this type of experiment. The radiated power is in good agreement with the predictions of the surface current description of this process. It is concluded that 90% of the bunch particles are contained within 5.5 ps, with a temporal profile that could be approximately triangular in shape.
Highlights
The term Smith-Purcell (SP) radiation is used to describe the radiation produced through the interaction of a beam of charged particles with a periodic metallic structure, e.g., a grating [1]
The wavelength region of the emitted radiation depends on the chosen periodicity of the grating and can, be selected
The motivation behind the present work is threefold: (a) to extend the previous work to beams of higher energy and shorter bunch length; this is an essential step before progressing to GeV beams, (b) to verify the suitability of room-temperature detectors for the measurement of SP radiation and the consequent simplification of the experimental setup, (c) to explore the validity of the ‘‘surface current‘‘ treatment of the radiative process in the 45–50 MeV regime
Summary
The term Smith-Purcell (SP) radiation is used to describe the radiation produced through the interaction of a (usually relativistic) beam of charged particles with a periodic metallic structure, e.g., a grating [1]. We concentrate on the one that describes the emission in terms of currents induced on the grating surface by an electron bunch passing close to the surface and perpendicular to the grooves [10 –12] This is a treatment that has provided good agreement between theory and measured radiated power, with the exception of one experiment at about 850 MeV [13] where special circumstances could have affected the results. On the other hand, choosing a period much longer than the bunch length will result in full coherence of the emitted radiation and consequent loss of the information on the wavelength (angular) distribution of the radiated power.
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