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Title: An Investigation into the Design of the Helical Undulator for the International Linear Collider Positron Source
Author: Scott, Duncan James
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2008
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Abstract:
Positrons are produced in the International Linear Collider via pair-production when multi-MeV photons are incident on a metallic conversion target. The multi-1IeV photons are generated by the main electron beam, at an energy of 150 GeV, which passes through a ',200 m long helical undulator magnet and generates synchrotron radiation. The circular polarisation of the helical undulator radiation can be used to create a polarised positron source. A derivation, from i\la-..;:well's equations, of the radiation characteristics of a helical undulator is presented. After a comprehensive paper study of possible undulator designs the two pre-eminent ones were fabricated and tested. A super-conducting bifilar wires undulator was chosen instead of a permanent magnet design. This was because of its superior performance in terms of, magnetic field strength and quality, operational flexibility, risk of radiation damage, ease in achieving the required vacuum and cost. For a beam aperture of ''5.85 mm and operational safety margin of ''80% the period and strength of the undulator are 11.5 nUll and 0.9 T, respectively. The magnetic field errors are shown to be acceptable for an unpolarised positron source. To meet the required vacuum level a series of photon collimators with a diameter of 4.4 mm are required. To mitigate impedance effects a smooth copper vessel with surface roughness'' 100 nm should be used. The impedance effects on the electron beam of the photon collimators and other tapered elements in the undulator line are also shown to be acceptable.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Liverpool, 2008 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.490620  DOI: Not available
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