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

Funding: * This work is funded by 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 containment of beams in the longitudinal direction is fundamental to the operation of accelerators that circulate high intensity beams for long distances such as the University of Maryland Electron Ring (UMER); a scaled accelerator using low-energy electrons to model space-charge dynamics. The longitudinal space-charge forces in the beam, responsible for the expansion of the beam ends, cause a change in energy at the beam head/tail with respect to the main injected energy or flat-top part of the beam. This paper presents the first experimental results on using an induction cell to longitudinally focus the circulating beam within the UMER lattice for multiple turns.

Keywords: electron ring, focusing, induction cell.

• 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.

• K. Fiuza, B.L. Beaudoin, S. Bernal, I. Haber, R.A. Kishek, P.G. O'Shea, M. Reiser, D.F. Sutter
  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.

Understanding the dynamics of the acceleration of high-intensity space-charge-dominated electron and ion beam is very important. Accelerating by steps a space-charge-dominated beam can be fundamentally different from beams at lower intensities, because at sufficiently high beam intensities the beam response to acceleration can drive to some unknown instabilities leading to a significant beam losses. This work analyses the acceleration of the University of Maryland Electron Ring (UMER) beam, i.e., high current, low-energy and space-charge-dominated electron beam which is applicable, on a scale basis, to a large class of other beam systems. We use the WARP particle-in-cell code to perform simulations that are compared with theoretical predictions and preliminary experimental results.

• 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.

• C. Wu, E.H. Abed, B.L. Beaudoin, S. Bernal, K. Fiuza, I. Haber, R.A. Kishek, P.G. O'Shea, M. Reiser, D.F. Sutter
  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.

Beam centroid control is an important method for optimizing the performance for accelerators, including the University of Maryland Electron Ring (UMER), which is a scaled low-energy (10KeV) storage ring. The conventional response matrix and singular value decomposition approach do not work well on the UMER because of the unique ring structure. One of the purposes of this work is to verify that the beam centroid could be controlled in the presence of very strong space charge. In this paper, we present a novel algorithm which is based on the singular value decomposition, but uses a different response matrix, which is computed from the closed equilibrium orbit and beam positions up to the first four turns in the multi-turn beam circulation. Other issues like strong coupling between the horizontal steering dipoles and vertical steering dipoles in the beam injection section will be addressed. Implementation of this algorithm leads to significant improvement on the beam positions and multi-turn operation.