Measurement of subpicosecond bunch lengths using coherent Smith-Purcell radiation

Coherent Smith-Purcell (SP) radiation originating from three different gratings has been measured at End Station A, SLAC, and has been used to reconstruct the time profile of the electron bunches. The beam energy during these experiments was 28.5 GeV ( ffi 55 773) and the number of electrons in the bunch was 0:9-1:4 Â 10 10 . The spectral distribution of the radiated energy was measured by means of an array of 11 pyroelectric detectors. Typical values of the FWHM of the bunch length are about 2.5 ps, but sharper peaks with FWHM less than 2.0 ps have also been observed. The longitudinal profile also varies with accelerator conditions and can best be approximated by a superposition of 3-4 Gaussian curves. Some typical profiles are presented, together with a discussion of the limitations and strengths of coherent SP radiation as a diagnostic tool. It is concluded that SP radiation offers excellent prospects in this respect, not only in the picosecond range, but potentially in the femtosecond range as well.

Section: A General Commentsmentioning

confidence: 99%

First measurements of the longitudinal bunch profile of a 28.5 GeV beam using coherent Smith-Purcell radiation

Blackmore

Doucas

Perry

et al. 2009

“…These properties, together with the fact that the emission of SP radiation causes minimal disruption to the beam, make SP particularly promising as a diagnostic tool for the determination of the longitudinal (time) profile of charged particle bunches. SP radiation has already been used to determine the longitudinal profile of 14 ps long bunches at low energies [2,3] and at 15 MeV [4]. 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.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal electron bunch profile diagnostics at 45 MeV using coherent Smith-Purcell radiation

Doucas

Blackmore

Ottewell

et al. 2006

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.

“…Thus SPR can be used as a nondestructive bunch-length diagnostic tool by determining the angle of cutoff in coherent radiation [4,5]. Subpicosecond bunch-length measurements were obtained by measuring the angular SPR pattern from 15 MeV bunches [6]. Other diagnostics may include a position sensor for ultrarelativistic beams [7] and an electron bunch shape measurement [8].…”

Section: Introductionmentioning

confidence: 99%

Power measurement of frequency-locked Smith-Purcell radiation

Kesar

Marsh

Temkin

2006

Frequency-locked Smith-Purcell radiation (FL-SPR), generated by a train of electron bunches traveling above a grating, is characterized by a broad range of frequencies which are locked to the train frequency in a discrete comb and are spatially dispersed in space. We report absolute-scale power measurement of FL-SPR in the millimeter wave range. A 50 ns long train of 170 m electron bunches was produced by a 15 MeV, 17 GHz accelerator with 80 mA of average current. The grating had 20 periods spaced by 2.54 mm. The experimental results were compared, on an absolute scale, with the electric-field integral equation model which takes into consideration the finite length of the grating. Very good agreement was obtained. The present results should be useful in planning SPR applications such as diagnostics of electron bunch length on the femtosecond scale and coherent THz radiation sources.