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Bernal, S.

Paper Title Page
MPPE067 Refined Calculation of Beam Dynamics During UMER Injection 3733
 
  • G. Bai, S. Bernal, T.F. Godlove, I. Haber, R.A. Kishek, P.G. O'Shea, B. Quinn, J.C. Tobin Thangaraj, M. Walter
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by U.S. Dept. of Energy under grants DE-FG02-94ER40855 and DE-FG02-92ER54178.

The University of Maryland Electron Ring (UMER) is built as a low-cost testbed for intense beam physics for benefit of larger ion accelerators. The beam intensity is designed to be variable, spanning the entire range from low current operation to highly space-charge-dominated transport. The ring has recently been closed and multi-turn commissioning has begun. Although we have conducted many experiments at high space charge during UMER construction, lower-current beams have become quite useful in this commissioning stage for assisting us with beam steering, measurement of phase advance, etc. One of the biggest challenges of multi-turn operation of UMER is correctly operating the Y-shaped injection section, hence called the Y-section, which is specially designed for UMER multi-turn operation. It is a challenge because the system requires several quadrupoles and dipoles in a very stringent space, resulting in mechanical, electrical, and beam control complexities. This paper presents a simulation study of the beam centroid motion in the injection region.

 
TPAT004 Strongly Asymmetric Beams at the University of Maryland Electron Ring (UMER) 892
 
  • S. Bernal, R.A. Kishek, P.G. O'Shea, B. Quinn, M. Walter
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by U.S. Dept. of Energy under grants DE-FG02-94ER40855 and DE-FG02-92ER54178.

The standard operation of the University of Maryland electron ring employs symmetric strong focusing with magnetic quadrupoles, i.e., a FODO scheme whereby the zero-current betatron phase advances per period in the two transverse planes are equal or nearly so. Asymmetric focusing, on the other hand, employs quadrupoles with different strengths in a FODO cell. Typically, a small focusing asymmetry is implemented in most accelerators to set the operating point (horizontal and vertical zero-current tunes) in order to avoid resonances and/or compensate for edge focusing of bend magnets. Extreme asymmetry, however, is rarely, if at all, used. We review the motivation and theory of beam transport with general focusing asymmetry. We also present results of preliminary experiments and simulations with highly asymmetric focusing of a space-charge dominated electron beam in UMER.

 
TPAT066 Significance of Space Charge and the Earth Magnetic Field on the Dispersive Characteristics of a Low Energy Electron Beam 3691
 
  • R.A. Kishek, G. Bai, S. Bernal, T.F. Godlove, I. Haber, P.G. O'Shea, B. Quinn, C. Tobin, M. Walter
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by U.S. Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.

The combination of energy spread and space charge provides a rich domain for interesting beam dynamics that are currently not well understood. The University of Maryland Electron Ring (UMER) [1] is a small scaled ring designed to probe the little-known regions of higher beam intensities using low-energy electrons. As such, design, commissioning and operation of UMER present many challenges, some quite novel. For example the UMER beam energy of 10 keV makes the beam very sensitive to the Earth magnetic field, which we can fortunately use to assist in bending the beam. This paper presents a systematic simulation study of the interaction of space charge and energy spread, with and without the earth magnetic field.

*"Commissioning of the University of Maryland Electron Ring (UMER)," S. Bernal, et al., this conference.

 
TPPE046 Computer Simulation of the UMER Gridded Gun 2908
 
  • I. Haber, S. Bernal, R.A. Kishek, P.G. O'Shea, Y. Zou
    IREAP, College Park, Maryland
  • A. Friedman, D.P. Grote
    LLNL, Livermore, California
  • M. Reiser
    University Maryland, College Park, Maryland
  • J.-L. Vay
    LBNL, Berkeley, California
 
  Funding: This work is supported by the U.S. DOE under contract Nos. DE-FG02-02ER54672 and DE-FG02-94ER40855 at the UMD, and DE-AC03-76SF00098 at LBNL and W-7405-ENG-48 at LLNL.

The electron source in the University of Maryland Electron Ring (UMER) injector employs a grid 0.15 mm from the cathode to control the current waveform. Under nominal operating conditions, the grid voltage during the current pulse is sufficiently positive relative to the cathode potential to form a virtual cathode downstream of the grid. Three-dimensional computer simulations have been performed that use the mesh refinement capability of the WARP particle-in-cell code to examine a small region near the beam center in order to illustrate some of the complexity that can result from such a gridded structure. These simulations have been found to reproduce the hollowed velocity space that is observed experimentally. The simulations also predict a complicated time-dependent response to the waveform applied to the grid during the current turn-on. This complex temporal behavior appears to result directly from the dynamics of the virtual cathode formation and may therefore be representative of the expected behavior in other sources, such as some photoinjectors, that are characterized by a rapid turn-on of the beam current.

 
RPPE076 Overview of Electrical Systems for the University of Maryland Electron Ring (UMER) 3988
 
  • B. Quinn, G. Bai, S. Bernal, T.F. Godlove, I. Haber, J.R. Harris, M. Holloway, H. Li, J.G. Neumann, P.G. O'Shea, K. Tian, M. Walter
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by the United States Department of Energy under grants DE-FG02-94ER40855 and DE-FG02-92ER54178.

Commissioning of the University of Maryland Electron Ring (UMER) is underway (see general abstract on UMER). We discuss the various electrical systems of UMER. The power system includes 114 supplies for 70 air-core magnetic quadrupoles, 36 bending dipoles and 30+ steering dipoles as well as earth's field compensating coils. Systems for data collection comprise multiplexers and fast digitizers for diagnostics including 15 fast beam position monitors (BPMs)and video capture from fluorescent screen monitors. Several pulsers have been built in-house for injection and extraction magnets. The stringent timing schemes are also presented.

 
FPAE021 Alignment and Steering for Injection and Multi-Turn Operation of the University of Maryland Electron Ring (UMER) 1709
 
  • M. Walter, G. Bai, S. Bernal, I. Haber, M. Holloway, R.A. Kishek, P.G. O'Shea, B. Quinn
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.

The injection line and main lattice for the University of Maryland Electron Ring (UMER) has been completed. The electron beam has been guided around the full 360 degrees of the ring. Beam steering and matching in the injection line is achieved with six quadrupole magnets and several small steering dipole magnets. The dipole component of an offset quadrupole and a pulsed dipole are used to achieve the 10 degree bend required from the injection line into the ring. The pulsed dipole is designed to operate with a short pulse (2 kV, -30 A, 100 ns flat top duration) for injection superimposed on a long pulse (300 V, 15 A, 20·10-6 s duration) for multiple beam passes. The beam is controlled in the recirculating ring with a regular lattice of 36 dipole and 72 quadrupole magnets. Initial experimental results of the beam transport and control will be presented.

 
FOAD005 Commissioning of the University of Maryland Electron Ring (UMER) 469
 
  • S. Bernal, G. Bai, D.W. Feldman, R. Feldman, T.F. Godlove, I. Haber, J.R. Harris, M. Holloway, R.A. Kishek, J.G. Neumann, P.G. O'Shea, C. Papadopoulos, B. Quinn, D. Stratakis, K. Tian, J.C. Tobin Thangaraj, M. Walter, M. Wilson
    IREAP, College Park, Maryland
  • M. Reiser
    University Maryland, College Park, Maryland
 
  Funding: This work is funded by the U.S. Department of Energy under grants DE-FG02-94ER40855 and DE-FG02-92ER54178, and the office of Naval Research under grant N00014-02-1-0914.

The University of Maryland electron ring (UMER) is a low-energy, high current recirculator for beam physics research. The ring is completed for multi-turn operation of beams over a broad range of intensities and initial conditions. UMER is addressing issues in beam physics with relevance to many applications that rely on intense beams of high quality. Examples are advanced accelerators, FEL’s, spallation neutron sources and future heavy-ion drivers for inertial fusion. We review the motivation, ring layout and operating conditions of UMER. Further, we present a summary of beam physics areas that UMER is currently investigating and others that are part of the commissioning plan: from transverse beam dynamics (matching, halo formation, strongly asymmetric beams, space-charge waves, etc), longitudinal dynamics (bunch capture/shaping, evolution of energy spread, longitudinal space-charge waves, etc.) to future upgrades and planned research (acceleration and resonance traversal, modeling of galactic dynamics, etc.) We also emphasize the computer simulation work that is an integral part of the UMER project.