Abstract
Transverse beam profile diagnostics in linear electron accelerators is usually based on direct imaging of a beam spot via visible transition radiation. In this case the fundamental resolution limit is determined by radiation diffraction in the optical system. A method to measure beam sizes beyond the diffraction limit is to perform imaging dominated by a single-particle function (SPF), i.e. when the recorded image is dominated not by the transverse beam profile but by the image function of a point source (single electron). Knowledge of the SPF for an experimental setup allows one to extract the transverse beam size from an SPF dominated image. This paper presents an approach that allows one to calculate two-dimensional SPF dominated beam images, taking into account the target inclination angle and the depth-of-field effect. In conclusion, a simple fit function for beam size determination in the case under consideration is proposed and its applicability is tested under various conditions.
Highlights
INTRODUCTIONFor example the linear collider projects ILC or CLIC, linear accelerator (linac) based free electron lasers (FELs), and electron beam driven plasma accelerators, require electron beam sizes in the order of 10 μm down to submicrometers
Generation electron accelerators, for example the linear collider projects ILC or CLIC, linear accelerator based free electron lasers (FELs), and electron beam driven plasma accelerators, require electron beam sizes in the order of 10 μm down to submicrometers
Using existing OTR single-particle function (SPF) models which are based on axial symmetry in the observation geometry the banana-shaped beam images could not be explained, and instead numerical simulations were carried out based on commercial ray tracing software [22]
Summary
For example the linear collider projects ILC or CLIC, linear accelerator (linac) based free electron lasers (FELs), and electron beam driven plasma accelerators, require electron beam sizes in the order of 10 μm down to submicrometers. Transverse beam profile diagnostics based on transition radiation is a standard technique at electron linacs This radiation is emitted when a beam of charged particles crosses the boundary between two media with different optical properties. Imaging with coherent and incoherent transition radiation at flat and rough target surfaces was discussed by Stupakov [16] Following these references the SPF has a double-lobe structure which is defined by the radiation wavelength λ, the acceptance angle or numerical aperture of the optical system θm, and the alignment accuracy. Using existing OTR SPF models which are based on axial symmetry in the observation geometry the banana-shaped beam images could not be explained, and instead numerical simulations were carried out based on commercial ray tracing software [22]. A new fit function for SPF dominated beam imaging is proposed which allows a direct and fast beam size determination, paving the way for application of the method in online emittance diagnostics with submicron electron beams
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