Abstract
We report the use of coherent Smith-Purcell radiation to measure the bunch length of femtosecond-scale, 15 MeV electron bunches produced by a 17 GHz rf accelerator. The Smith-Purcell radiation was produced by passing a train of electron bunches above a metal grating. The radiation was verified as Smith-Purcell radiation by measuring the resonance condition, dependence on beam current, and dependence on beam height above the grating. Measurements of the intensity of the radiation vs emission angle were analyzed to obtain the bunch length. The accelerator was operated in two different modes, producing bunches that were determined to have bunch lengths of 600 and $1000\ifmmode\pm\else\textpm\fi{}200\text{ }\text{ }\mathrm{fs}$. These nondestructive bunch length measurements were found to agree well with an independent, but destructive, measurement using a microwave deflecting cavity.
Highlights
The measurement and diagnosis of ultrashort, i.e., subpicosecond, electron bunches is important for linear colliders, free electron lasers (FELs) and plasma accelerators
The electron beam is produced by a linac, built by Haimson Research Corporation (HRC), which consists of a 515 kVelectron gun, a chopper-prebuncher and three lens injector and a quasiconstant gradient accelerating structure consisting of 94 cavities that operate in the 2=3 mode [22]
The linac is powered by the HRC relativistic klystron [23,24] which was typically operated at 15 MW of rf power at 17.140 GHz in 100 ns pulses
Summary
The measurement and diagnosis of ultrashort, i.e., subpicosecond, electron bunches is important for linear colliders, free electron lasers (FELs) and plasma accelerators. Various different techniques have demonstrated the measurement of subpicosecond bunch lengths including streak cameras [1], rf deflecting structures [2,3], electro-optic techniques [4], coherent synchrotron radiation [5,6], and coherent diffraction radiation [7,8]. One of the most promising bunch length measurement techniques, which has minimal effect on the beam, is. SPR, which occurs when a charged particle passes over a periodic structure, was first observed in 1953 [11]. SPR has several advantages over other coherent radiation generation techniques such as synchrotron, transition and diffraction radiation
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