Abstract
High-resolution measurement of the longitudinal profile of a relativistic electron beam is of utmost importance for linac based free-electron lasers and other advanced accelerator facilities that employ ultrashort bunches. In this paper, we investigate a novel scheme to measure ultrashort bunches (subpicosecond) with exceptional temporal resolution (hundreds of attoseconds) and dynamic range. The scheme employs two orthogonally oriented deflecting sections. The first imparts a short-wavelength (fast temporal resolution) horizontal angular modulation on the beam, while the second imparts a long-wavelength (slow) angular kick in the vertical dimension. Both modulations are observable on a standard downstream screen in the form of a streaked sinusoidal beam structure. We demonstrate, using scaled variables in a quasi-1D approximation, an expression for the temporal resolution of the scheme and apply it to a proof-of-concept experiment at the UCLA Neptune high-brightness injector facility. The scheme is also investigated for application at the SLAC NLCTA facility, where we show that the subfemtosecond resolution is sufficient to resolve the temporal structure of the beam used in the echo-enabled free-electron laser. We employ beam simulations to verify the effect for typical Neptune and NLCTA parameter sets and demonstrate the feasibility of the concept.
Highlights
Generation free-electron lasers (FELs), such as the Linac Coherent Light Source (LCLS), and other advanced accelerator facilities require ultrashort pulses ($ few femtoseconds) with high peak currents (* 103 A) for successful operations
Reasonable longitudinal characterization of these short beams demands a resolution on the femtosecond scale or better, in order to study phenomena on the ultrashort length or ultrafast time scales such as the microbunching instability behind the observation of coherent optical transition radiation [2,3,4], the longitudinal beam properties of echo-enabled FELs [5], the properties of drivers for attosecond x-ray production [6], or beam studies in single-spike self-amplified spontaneous emission FEL processes [7]
To get a sense of the characteristics of the system for some general scaling, we model the arrangement as three simple components: (1) the laser modulator, (2) the rf deflector, and (3) the drift to the diagnostic screen
Summary
Generation free-electron lasers (FELs), such as the Linac Coherent Light Source (LCLS), and other advanced accelerator facilities require ultrashort pulses ($ few femtoseconds) with high peak currents (* 103 A) for successful operations. Present-day bunch length diagnostics include a wide range of schemes including electro-optical techniques [8], rf deflecting cavities [9], rf zero-crossing methods [10], and the deconvolution of the frequency spectrum of emitted radiation sources [11,12]. These methods are well tested and robust, with resolutions reported as low as
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