Date of Completion

8-21-2017

Embargo Period

8-23-2017

Keywords

laser ablation, diamond radiator, linearly polarized photon beam, GlueX, coherent bremsstrahlung

Major Advisor

Richard Jones

Associate Advisor

Thomas Blum

Associate Advisor

Andrew Puckett

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The GlueX Experiment conducted in Newport News, VA requires a 9 GeV beam of linearly polarized photons to access the physics of gluonic excitations. Coherent bremsstrahlung (CB) was chosen as the radiation technique for its high intensity and degree of linear polarization. The CB radiator must be of sufficient crystal quality and have appropriate material properties for operating in a 12 GeV electron beam. Diamond, due to its high Debye temperature, was chosen as the CB radiator. Due to multiple scattering of the electron through the crystal, the central region of the radiator is constrained to a thickness of 20 µm. The overall crystal quality must be high in order to reduce the photon beam emittance for proper collimation of unpolarized photons. To meet this specification, the diamond must not have a whole-crystal rocking curve greater than the electron beam emittance, on the order of 20 µrad. This work describes the development of a novel laser ablation technique for differentially thinning single-crystal CVD diamond plate to meet the strict GlueX requirements. Transmission mode x-ray rocking curve measurements are presented which are used to characterize the diamond radiator lattice structure (mosaic spread) before and after laser ablation. Finally, an analysis of the ρ vector meson decay channel γp → π +π −p is discussed and used to extract the product of the beam asymmetry and polarization of the photon beam as well as spin density matrix elements (SDMEs) in the helicity reference frame. The observables measured from this analysis are strongly correlated to the performance of the diamond radiator used to produce the linearly polarized photon beam.

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