UMD, College Park, Maryland, USA
Characterization of the transverse phase space of electron beams with space charge is an important requirement for high brightness particle accelerators. We present a novel technique to measure the transverse rms emittance. The method uses the beam divergence, measured, e.g. with optical transition radiation interferometry*, and the beam radius, obtained by imaging the beam, to determine the cross correlation term and thus all the terms in the equation for the rms emittance. The experimental data is obtained with a lens-drift-screen setup similar to what is used in a quadrupole scan. However, the analysis of the scan data is unique. It involves taking the cross-correlation term as a control variable in a procedure which matches the beam envelop radius and its derivative calculated from the envelope equation, with the measured radius and divergences at the screen. A linear space charge model is used in the envelope equations, hence the errors in the measurement relate to the nonuniformity of the beam transverse distribution. The technique is tested using simulated data.
* R. B. Fiorito, et al., “Interference of diffraction and transition radiation and its application as a beam divergence diagnostic,” Phys. Rev. ST Accel. Beams, Vol. 9, pp. 052802, (2006).
FROAA1
UMD, College Park, Maryland, USA
Space charge, especially in the beam source and low energy regions, can substantially impact the dynamics of advanced accelerators at the intensity frontier. UMER uses scaled electron beams at nonrelativistic energies (10 keV) to inexpensively access the intense space charge dynamics directly relevant to low-energy hadron and ion beams, in both rings and linacs. In UMER, space charge tune depressions at injection are adjustable in the range of 0.14 - 0.8, enabling scaled examination of a wide range of phenomena. Longitudinal induction focusing is used to counteract the space charge force at the edges of a long rectangular bunch, confining it for 100s of turns. This paper reviews recent experimental, computational, and theoretical research on UMER. Specific topics include longitudinal induction bunch-end focusing; generation and propagation of longitudinal space charge waves, including large-amplitude solitons; bunch end interpenetration and observation of a resulting multi-stream instability; beam halo studies; beam current-dependence of classical ring parameters (natural chromaticity, lattice dispersion and momentum compaction); and diagnostic development.
UMD, College Park, Maryland, USA
Beam halos are a group of particles with low density that far away from the well-defined central beam core and have large transverse velocities. Beam losses from halos can require a larger aperture and impose restrictions on the beam current. Several theoretical techniques have been applied to analyze and understand halo formation, including particle-core model, free energy model as well as particle in cell (PIC) simulations. However, few experiments on beam halos have been carried out. Here, we describe an experimental study at the University of Maryland to understand and characterize space-charge induced halo formation. The experiments are conducted on the University of Maryland Electron Beam (UMER) and the results are compared with PIC simulations using WARP.