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Optical Transition Radiation. Beam profile measurements with. Klara Insulander Bj örk, Chalmers University of Technology, Gothenburg, Sweden. Outline. Beam diagnostics? Physical principle Mathematical description Beam profile measurement The BIBLE Summary. Beam diagnostics?.
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Optical Transition Radiation Beam profile measurements with Klara Insulander Björk, Chalmers University of Technology, Gothenburg, Sweden
Outline • Beam diagnostics? • Physical principle • Mathematical description • Beam profile measurement • The BIBLE • Summary
Beam diagnostics? • You need to know stuff about your beam: - If it is there at all - Where it is - What size and shape it has - How it evolves in time - Its energy, etcetera… • Measurements using Optical Transition Radiation (OTR) involve letting the beam pass through a foil ► It is mostly used for profile measurements
Physical principle • A charged particle moves through vacuum with its accompanying Coulomb field • It hits a foil of a medium having a different dielectric constant • The Coulomb field adapts to the new medium • The difference in fields is emitted as transition radiation
The actual angular intensity distribution becomes: Mathematical description The angular intensity distribution is given by:
OTR is fast – resolution better than picosecond • Use a streak camera to get the longitudinal beam profile (bunch length and spacing) • Converts time variation into space variation Beam profile measurement • Put the camera in the image plane of the optical system to get a geometrical image of the beam • Information on transverse beam profile (beam size and shape)
The BIBLE • The acronym (of course) stands for Beam Instrumentation BookLEt, a pocket sized document for beam instrumentation users • My work – the chapter on OTR • The same information is also available as a webpage • Calculation of important parameters can be done with a Matlab program
Summary • You need to know stuff about your beam • Let it pass through a foil and you get OTR • Look at the angular distribution to get info on energy and divergence • Look directly at the image of the beam to get information on beam size, shape and position • Use a streak camera to get information on bunch length and spacing • Read the BIBLE in case you forget what I just told you Questions?