• S. Bernal, B.L. Beaudoin, M. Cornacchia, K. Fiuza, I. Haber, R.A. Kishek, T.W. Koeth, P.G. O'Shea, C. F. Papadopoulos, M. Reiser, D.F. Sutter, C. Wu
  UMD, College Park, Maryland

Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office

The University of Maryland Electron Ring (UMER) can operate over a broader range of beam intensities than other circular machines. Naturally, transverse and longitudinal space charge effects limit the ability to store beams. In UMER, the resonance properties of the machine in the two regimes of operation, emittance- and space charge-dominated transport, differ significantly. We report on studies of linear betatron resonances in UMER from 0.6 mA to 80 mA beam current, corresponding to theoretical space charge incoherent tune shifts well over the Lasslet limit. The observations are related to existing theories as well as to computer simulations. We also describe the instrumentation and techniques used for tune measurements.

• R.A. Kishek, B.L. Beaudoin, S. Bernal, M. Cornacchia, I. Haber, P.G. O'Shea, M. Reiser, D.F. Sutter, J.C.T. Thangaraj, C. Wu
  UMD, College Park, Maryland
• D. Stratakis
  BNL, Upton, Long Island, New York

Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office

Beam matching is critical for avoiding envelope mismatch oscillations that can lead to emittance growth and halo formation, especially if the beam has significant space charge. The University of Maryland Electron Ring (UMER) is a research storage ring that is designed for scaled studies that are applicable to many larger machines. Using 10 keV electron beams at relatively high current (0.6 – 100 mA), space charge forces are relatively strong. Matching of the UMER beam is rendered difficult by the space charge, the crowdedness of the lattice, and especially the unique injection scheme where an offset oversized quadrupole is shared between the ring and the injector. In this paper we discuss several schemes for optimizing the matching at injection, both analytical and beam-based, which we test using particle-in-cell simulations with the code, WARP. Comparison to UMER experimental data is provided where available.

• D.F. Sutter, B.L. Beaudoin, S. Bernal, M. Cornacchia, K. Fiuza, I. Haber, R.A. Kishek, P.G. O'Shea, M. Reiser, C. Wu
  UMD, College Park, Maryland

Funding: *This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office

The University of Maryland Electron Ring (UMER) is designed for operation over a broad range of beam intensities, including those normally achieved only in linacs. This is possible thanks to a combination of low-energy (10 keV) electrons and a high density of magnetic quadrupoles (72 over an 11.5 m circumference) that allow operation from 0.5 mA to 100 mA; that is, from the emittance dominated to the highly space charge dominated regimes. We present results of basic centroid-motion characterization, including measurements of closed-orbit distortion, momentum compaction factor, and natural chromaticity and dispersion. These are compared with results from computer simulations employing the code ELEGANT. We discuss the techniques and challenges behind the measurements with fast beam-position and wall-current monitors, and also the special role of the background ambient magnetic field for beam steering.