Ph.D. Dissertation Defense: Hao Zhang
Wednesday, December 11, 2013
1:00 p.m. Room 1207, Energy Research Facility
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ANNOUNCEMENT: Ph.D. Dissertation Defense
Name: Hao Zhang
Professor Rami Kishek, Chair / Advisor
Professor Patrick O'Shea, Co-Chair / Advisor
Professor Thomas Antonsen
Professor Victor Grananstein
Professor Adil Hassam, Dean's representative
Date/Time: Wednesday, December 11th, 2013 at 1:00 pm.
Location: Room 1207, Energy Research Facility (Large Conference Room in IREAP)
Title: Experimental study of beam halo in intense charged particle beams.
Beam halo is a group of particles with low density that are far away from the well-defined central beam core or that have large transverse velocities. It is a common phenomenon which occurs in most intense particle accelerators because of the self space charge forces. Even for low intensity particle beam, 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 require a larger aperture and impose restrictions on the beam current. In this dissertation, I address the halo phenomenon in intense charged particle beams. Although most of the study is based on the University of Maryland Electron Ring, it is applicable to a wide range of accelerators in the same intensity regime.
I first discuss a match procedure and rotation correction for envelope match. The gradients of four quadruples in the injection are independently adjusted to match or mismatch the beam. The gradients of two skew quadruples in the injection are independently adjusted to correct the beam rotation. I succeed in matching the UMER beam with 6mA, 21mA and 80 mA beam current 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.
Following the previous work, I simulate the halo formation in UMER lattice till RC12 (about 10 mismatch oscillations) with higher beam intensity in the frame of two envelope mismatch modes. In experiment, I succeed in generate pure mode envelope mismatch with a wide range of the mismatch 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 halo particle radius predicted by a particle-core model. The experiments support both the simulation and the theory with reasonable satisfactory.
I also further investigate the adaptive masking method for halo imaging, and applied it for halo diagnostic at JLAB FEL facility and for injected beam imaging at SLAC SPEAR3.