Abstract
Coherent enhancement of the Smith-Purcell radiation produced from the interaction of a 1.8 MeV electron beam with a grating has been observed. The emitted radiation has been measured at angles in the 40± to 120± range, which correspond to wavelengths from 0.65 to 4 mm, approximately. The radiated power was 320 mW at 90±. Its angular distribution agrees well with the description of the process in terms of induced surface currents and has been used to infer the longitudinal profile of the electron bunch. It is concluded that the bunch has an approximately triangular profile, with 85% of the bunch particles contained within 14 ps. The possibilities of the technique as a bunch-shape diagnostic tool are also discussed.
Highlights
Noninvasive beam diagnostic techniques are likely to play an important role in the generation of highenergy electron accelerators, whether these are used for particle physics (“Linear Collider”) or as sources for x-ray free electron lasers (FELs)
We have considered a number of plausible time profiles ftand have evaluated the coherent integral in each case: Gaussian, triangular, exponential, parabolic, and cosinelike
We have measured the absolute power levels of coherent Smith-Purcell radiation produced by the interaction of a 1.8 MeV electron beam and a blazed grating with a period of 2.5 mm and blaze angle of 14±
Summary
Noninvasive beam diagnostic techniques are likely to play an important role in the generation of highenergy electron accelerators, whether these are used for particle physics (“Linear Collider”) or as sources for x-ray free electron lasers (FELs). One possible method of obtaining information about certain properties of the beam, such as longitudinal profile of the bunch, is by observing the radiation emitted through the interaction of the beam with a medium The oldest of these “optical” techniques is based on transition radiation (TR), produced by the passage of the bunch through a very thin foil. A very recent addition to the armory of noninvasive techniques is the measurement of bunch duration and shape by means of the detection of the electric field of the relativistic electron as it passes close to a crystal of ZnTe [8] Another process that is nonintercepting and causes minimal disruption to the electron beam is the so-called SmithPurcell radiation (SPR), which is the radiation produced by the interaction of the electron with a periodic structure, such as a metallic grating. We report on the results of recent experiments carried out at the ENEA facility at Frascati, Rome, and consider the potential of coherent SPR as a pulse-shape diagnostic tool for picosecond electron bunches
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