Browsing by Author "Tian, Kai"
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Item STUDY OF LONGITUDINAL DYNAMICS IN SPACE-CHARGE DOMINATED BEAMS(2008-04-07) Tian, Kai; O'Shea, Patrick G; Kishek, Rami A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Modern accelerator applications, such as heavy ion fusion drivers, pulsed neutron sources, electron injectors for high-energy linear colliders, and X-ray Free Electron Lasers, demand beams with high intensity, low emittance and small energy spread. At low (non-relativistic) energies, the "electrostatic", collective interactions from space-charge forces existing in such intense beams play the dominant role; we characterize these beams as space-charge dominated beams. This dissertation presents numerous new findings on the longitudinal dynamics of a space-charge dominated beam, particularly on the propagation of density perturbations. In order to fully understand the complex physics of longitudinal space-charge waves, we combine the results of theory, computer simulation, and experiment. In the Long Solenoid Experimental system (LSE), with numerous diagnostic tools and techniques, we have, for the first time, experimentally measured the detailed energy profiles of longitudinal space-charge waves at different locations, both near the beam source and at the end of the transport system. Along with the current profiles, we have a complete set of experimental data for the propagation of space-charge waves. We compare these measured results to a 1-D theory and find better agreement for beams with perturbations in the linear regime, where the perturbation strength is less than 10%, than those with nonlinear perturbations. Using fast imaging techniques that we newly developed, we have, for the first time, obtained the progressive time-resolved images of longitudinal slices of a space-charge dominated beam. These images not only provide us time-resolved transverse density distribution of the beam, but also enable us to take time-resolved transverse phase space measurement using computerized tomography. By combining this information with the longitudinal energy measurement, we have, for the first time, experimentally constructed the full 6-D phase space. Part of the results from the 6-D phase space measurement has been used as initial conditions in computer simulations in order to explore the cause of discrepancies we have observed earlier between the experimental and theoretical models. After extensive simulation studies, we find that the beam loss inside the perturbation due to mismatch or misalignment is an important factor that needs to be included in the models for better reliability.Item STUDY OF SPACE-CHARGE WAVES IN A LONG SOLENOID CHANNEL(2005-04-27) Tian, Kai; O'Shea, Patrick G; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, studies of the dynamics of longitudinal space-charge waves in space-charge dominated beams propagating through a transport channel with a long solenoid are performed. First, some basic models of space-charge waves behaviors are reviewed. Second, WARP simulations on generating either pure fast waves or pure slow waves are presented. Then experimental studies on the energy modulations converted from density modulations are reported. By changing the working conditions of the electron gun, pure initial density modulations are generated. Energy perturbation waveforms are measured by a high resolution energy analyzer. Finally, the experimental results are compared with both the linear theory and the WARP simulation results. Good agreements are achieved for the relationship between the energy and current perturbation strengths. The notable exception is a large discrepancy between experiment and theory for the speed of sound at differing perturbation strengths, which remains to be investigated in future work.