UMD, College Park, Maryland, USA
We report on experiments and simulations of beam lifetime at the University of Maryland Electron Ring (UMER) for an emittance as well as a strongly space-charge dominated beam. The beam transmission is studied by-the-turn for over 2,000 operating tunes; for this, the ring quadrupoles in the 11.52m-circumference ring are powered over a range of currents corresponding to bare tunes in the range 5.5 to 8.0 approximately. The main beam parameters of the electron beams at 10 keV are 0.6 and 6.0 mA, 0.4 and 1.3 μm initial normalized rms emittances, and 100 ns bunch duration. We note the presence of expected (and strong) integer resonances for both beam currents and the absence, for moderate envelope mismatch, of some half-integer resonances for the high current beam only. The observations are related to existing theory and to particle-tracking simulations with the matrix code Elegant. The simulations employ a simple incoherent space charge model for a continuous beam, as well as different lattice and magnet errors and orders of calculation.
UMD, College Park, Maryland, USA
The University of Maryland Electron Ring (UMER) normally injects a beam that is square in longitudinal profile (constant line density), filling one half the ring. When operating without longitudinal focusing, the beam head and tail erode at a constant plasma wave speed. Because the beam is very long (580 cm) compared to the beam pipe diameter (5 cm), the two eroding edges remain sharply defined until they meet. This paper describes how the plasma wave speed in the beam can be obtained experimentally by measuring only the initial pulse length, the time it takes for the eroding ends to meet and the kinetic energy. The plasma wave velocity can then be used to get an estimate of the average beam radius during the erosion time. Experimental results are compared to theoretical predictions and to measurements of the plasma wave velocity obtained from induced plasma density wave measurements.
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.
