Generation of short pulse THz radiation from accelerator based light sources
<p>High power and short pulse THz radiation has become increasingly important in the investigation of dynamics of organic and chemical molecules. Such radiation can be effectively generated with accelerator-based light sources. This thesis reports a series of studies on the generation of short...
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2016
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| Summary: | <p>High power and short pulse THz radiation has become increasingly important in the investigation of dynamics of organic and chemical molecules. Such radiation can be effectively generated with accelerator-based light sources. This thesis reports a series of studies on the generation of short pulse THz radiation from storage rings and from compact accelerators that can be based in University sized laboratories. The first part of this thesis reviews THz radiation, synchrotron radiation and free electron laser (FEL). The second part presents the studies of short pulse THz radiation generated from the Diamond storage ring in a new operating mode known as ultra-low alpha mode to extend spectrum of coherent radiation to higher THz frequency. The numerical simulations of a single bunch dynamics show qualitative agreements with the measurements taken at the Diamond storage ring. The third part is dedicated to the design of a compact RF linac-based THz radiation source for producing short pulse THz self-amplified spontaneous emission (SASE) FEL with an undulator and THz coherent synchrotron radiation (CSR) with a bending magnet. Start-to-end simulations of SASE FEL and CSR were performed to analyse the beam dynamics and the generation of THz radiation. The SASE FEL reaches saturation within the undulator length of 5 m, whereas the CSR spectrum covers frequency below 16 THz. In the fourth part, we investigated a THz/IR radiation source driven by a Laser Plasma Wakefield Accelerator (LPWA). Extensive 2D particle-in-cell (PIC) simulations were done to generate an ultra-short electron bunch from self-injection in a nonlinear bubble regime. The 60-MeV electron bunch was obtained with 6% energy spread and 18 mrad beam divergence. The self-injected electron beam was used to drive the SASE FEL using a normal undulator and a transverse gradient undulator (TGU) to exploit the electron bunch with large energy spread. The results show that the energy spread of 6% is too large even for the TGU. Although the energy spread is reduced to 1%, the FEL saturation cannot be reached because the bunch length of the LPWA driven beam is shorter than the FEL cooperation length. The last part of this thesis discusses the Accelerator Science Laboratory (ASL) project at the University of Oxford. The designs of THz radiation sources driven by the RF linac and the LPWA previously presented were considered as potential options for the ASL. The radiation shielding for the ASL was investigated with Monte Carlo simulations to design a proper beam dump and shielding covering the beam dump.</p> |
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