• C. F. Papadopoulos, R.B. Fiorito, R.A. Kishek, P.G. O'Shea, A.G. Shkvarunets
  UMD, College Park, Maryland
• M.E. Conde, W. Gai, J.G. Power
  ANL, Argonne

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.

Single foil OTR and two foil OTR interferometry have been successfully used to measure the size and divergence of electron beams with a wide range of energies. To measure rms emittance, two cameras are employed: one focused on the foil to obtain the spatial distribution of the beam, the other focused to infinity to obtain the angular distribution. The beam is first magnetically focused to a minimum size in directions which are orthogonal to the propagation axis, using a pair of quadrupoles. Then simultaneous measurements of the rms size (x,y) and divergence (x’,y’) of the beam are made. However, in the process of a quadrupole scan, the beam can go through a spot size minimum, a divergence minimum and a waist, i.e. the position where the cross-correlation term is zero. In general, the beam size, divergence and focusing strength for each of these conditions are different. We present new algorithms that relate the beam and magnetic parameters to the rms emittance for each of these three cases. We also compare the emittances, obtained using our algorithms and measurements made at the ANL AWA facility, with those produced by computer simulation.

• 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.

• C. F. Papadopoulos, S. Bernal, I. Haber, R.A. Kishek, P.G. O'Shea, M. Reiser
  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.

Halo is one important limiting factor for the continuous and reliable operation of intense electron or ion beam facilities, such as FELs and spallation neutron sources. A halo population outside the core of the beam can lead to uncontrolled beam loss, electron cloud effects and activation of the beam pipe, as well as beam quality degradation. In this study, we focus on the issue of halo removal, by means of beam collimation, and subsequent halo regeneration. We compare the particle-core model of halo creation to accurate, self consistent particle-in-cell (PIC) simulations. We show that under certain conditions the halo is regenerated even after collimation. This can only be understood within the context of collective effects, particularly in the case of intense beams.