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Polarized positron sources for the future linear colliders

Abstract : During the next few years experiments at the Large Hadron Collider (LHC) at CERN will continue to explore carefully fundamental high energy physics principles at a an energy domain which has never been reached before. Possible designs for the next-generation lepton Linear Collider (LC) based on e+–e- collisions have already been proposed to perform high precision studies complementary to the LHC. In this framework, there are two large projects: the International Linear Collider (ILC) exploring a centre-of-mass energy range of de s = 0.5 – 1 TeV and the Compact Linear Collider (CLIC) expected to operate at s = 0.5 – 3 TeV. The physics programme of the future LC will benefit strongly of colliding both polarised electron and positron beams. This thesis introduces the polarized positron source as one of the key element of the future LC. In this context, the different schemes of the polarized positron source are described highlighting the main issues in this technology. In particular, the main focus is on the Compton based positron source adopted by the CLIC as a preferred option for the future positron source upgrade. In this case, the circularly polarized high energy gamma rays resulting from Compton scattering are directed to a production target where an electromagnetic cascade gives rise to the production of positrons by e+–e- pair conversion. To increase the efficiency of the gamma ray production stage, a multiple collision point line integrated in energy recovery linac is proposed. The simulations of the positron production, capture and primary acceleration allow to estimate the positron production efficiency and provide a simple parametrization of the Compton based polarized positron source in the view of the future LC requirements. The storage ring based Compton source option, so-called Compton ring, is also described. The main constraint of this scheme is given by the beam dynamics resulting in the large energy spread and increased bunch length affecting the gamma ray production rate. An original theoretical contribution is shown to calculate the energy spread induced by Compton scattering. Moreover, an experiment to test the gamma ray production by Compton scattering using a state-of-art laser system developed at LAL has been conducted in the framework of the "MightyLaser" project at the ATF, KEK. The experimental layout as well as the main results obtained are discussed in details. The studies carried out in this thesis show that the polarized positron source based on Compton scattering is a promising candidate for the future LC polarized positron source. To attain the required performance, further developments and R&D in field of the high power laser systems, optical cavities and high current electron accelerators such as the energy recovery linacs should be pursued in the future.
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Submitted on : Friday, March 1, 2013 - 10:42:18 AM
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  • HAL Id : tel-00795937, version 1

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Iryna Chaikovska. Polarized positron sources for the future linear colliders. Other [cond-mat.other]. Université Paris Sud - Paris XI, 2012. English. ⟨NNT : 2012PA112358⟩. ⟨tel-00795937⟩

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