UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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Item Study and Mitigation of Transverse Resonances with Space Charge Effects at the University of Maryland Electron Ring(2020) Dovlatyan, Levon; Antonsen, Thomas M; Beaudoin, Brian L; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research at the intensity frontier of particle physics has led to the consideration of accelerators that push the limits on achievable beam intensities. At high beam intensities Coulomb interactions between charged particles generate a space charge force that complicates beam dynamics. The space charge force can lead to a range of nonlinear, intensity- limiting phenomena that result in degraded beam quality and current loss. This is the central issue faced by the next generation of high-intensity particle accelerators. An improved understanding of the interaction of the space charge forces and transverse particle motion will help researchers better design around these limiting issues. Furthermore, any scheme able to mitigate the impacts of such destructive interactions for space charge dominated beams would help alleviate a significant limitation in reaching higher beam intensities. Experimental work addressing these issues is presented using the University of Maryland Electron Ring (UMER). This dissertation presents experimental studies of space charge dominated beams, and in particular the resonant interaction between the transverse motion of the beam and the periodic perturbations that occur due to the focusing elements in a circular ring. These interactions are characterized in terms of the tune shifts, Qx and Qy, that are the number of transverse oscillations (in and out of the plane of the ring) per trip around the ring. Resonances occur for both integer and half-integer values of tune shift. Particle tune measurement tools and resonance detection techniques are developed for use in the experiment. Results show no shift for either the integer (Qx = 7.0, Qy = 7.0) or half-integer (Qx = 6.5, Qy = 6.5) resonance bands as a function of space charge. Accepted theory predicts only a shift in the half-integer resonance case. A second experiment testing the potential mitigation of transverse resonances through nonlinear detuning of particle orbits from resonance driving terms is also presented. The study included the design, simulation, and experimental test of a quasi-integrable accelerator lattice based on a single nonlinear octupole channel insert. Experiments measured a nonlinear amplitude dependent tune shift within the beam on the order of ∆Qx ≈ 0.02 and ∆Qy ≈ 0.03. The limited tolerances on accelerator steering prevented measuring any larger tune shifts.Item EXPERIMENTAL STUDY OF BEAM HALO IN INTENSE CHARGED PARTICLE BEAMS(2014) Zhang, Hao; Kishek, Rami A; O'Shea, Patrick G; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Beam halo is a common phenomenon that occurs in most intense particle accelerators, and refers to collections of particles that stray far away from a well-defined central beam core. Often in high-intensity beams, the space charge force induces halo. Even for low intensity accelerators, the beam halo could occur in the injection section before the particles are accelerated to relativistic speed. The most severe effects from beam halo are emittance growth and beam loss. Emittance growth can cause the degradation of beam quality, and beam losses will impose restrictions on the beam current. Although one can use a larger aperture to compensate this, the overall cost will increase exponentially. In this dissertation, we address the halo phenomenon and formation mechanism in intense charged particle beams. Although most of the experiment and simulation study of halo is based on the University of Maryland Electron Ring, it is applicable to a wide range of accelerators in the same intensity regime. We first discuss a matching procedure and rotation correction for the beam envelope. The gradients of four quadruples in the injection are independently adjust to match or mismatch the beam. The gradients of two skew quadruples in the injection are independently adjusted to correct the beam rotation. We succeed in matching the UMER beams and find out that the envelope mismatch and beam skewness are the major sources for halo formation in UMER. Halo could be drive out even in very early stage such as in 2 or 3 mismatch oscillations with large mismatch or beam rotation. We simulate the halo formation in UMER lattice till about 10 mismatch oscillations with higher beam intensity in the frame of two envelope mismatch modes. In experiment, we generate envelope mismatch mode with different mismatch level (parameter) by adjusting the four quadrupoles in the injection. The agreement of the envelope between experiments and simulations is satisfactory for mismatch parameter in the range of 0.8-1.2. Emittance and beam width are obtained from tomography and adaptive optical masking and imaging method separately for comparisons with the simulation as well as the maximum emittance growth predicted by a free energy model and maximum particle radius predicted by a particle-core model. The experiments confirm the predictions from both the simulation and the theory with reasonable agreement. We also further investigate the adaptive masking method for halo imaging, and apply it for halo diagnostics at JLAB FEL facility, and for imaging of the injected beam at the SLAC SPEAR3 storage ring.