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Bai, G.

Paper Title Page
MOPAS033 A Robust Orbit-Steering and Control Algorithm Using Quadrupole-scans as a Diagnostic 509
 
  • C. Wu, E. Abed, G. Bai, B. L. Beaudoin, S. Bernal, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, K. Tian, M. Walter
    UMD, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy.

Beam based alignment and control has been a critical issue for many accelerators. In this paper, we've developed a new approach that can correct the beam orbit using a systematic quad-scan method, where there is an insufficient number of beam position monitors. In this approach, we've proposed a calibrated response matrix. This matrix takes consideration of the different sensitivities of different quadrupoles in the lattice. With the calibrated response matrix, we can greatly enhance our ability to control the beam centroid motion and reduce the control effort.

 
TUZBAB03 The University of Maryland Electron Ring (UMER) Enters a New Regime of High-Tune-Shift Rings 820
 
  • R. A. Kishek, G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. Feldman, R. B. Fiorito, T. F. Godlove, I. Haber, T. Langford, P. G. O'Shea, C. Papadopoulos, B. Quinn, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, K. Tian, M. Walter, C. Wu
    UMD, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy and by the US Dept. of Defense Office of Naval Research.

Circular accelerators and storage rings have traditionally been designed with limited intensity in order to avoid resonances and instabilities. The possibility of operating a ring beyond the Laslett tune shift limit has been suggested but little tested, apart from a pioneering experiment by Maschke at the BNL AGS in the early 1980s. We have recently circulated the highest-space-charge beam in a ring to date in the University of Maryland Electron Ring (UMER), achieving a breakthrough both in the number of turns and in the amount of current propagated. At undepressed tunes of up to 7.6, the space charge in UMER is sufficient to depress the tune by nearly a factor of 2, resulting in tune shifts up to 3.6. This makes the UMER beam the most intense beam that has been propagated to date in a circular lattice. This is an exciting and promising result for future circular accelerators, and the UMER beam can now be used as a platform to study intense space charge dynamics in rings.

 
slides icon Slides  
TUPAS047 Multi-turn Operation of the University of Maryland Electron Ring (UMER) 1751
 
  • M. Walter, G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, T. F. Godlove, I. Haber, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, C. Wu
    UMD, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.

The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron beam current is adjustable from 0.7 mA, an emittance dominated beam, to 100 mA, a strongly space charge dominated beam. UMER is addressing issues in beam physics relevant to many applications that require intense beams of high quality such as advanced concept accelerators, free electron lasers, spallation neutron sources, and future heavy-ion drivers for inertial fusion. The primary focus of this presentation is experimental results and improvements in multi-turn operation of the electron ring. Transport of a low current beam over 100 turns (3600 full lattice periods) has been achieved. Results of high current, space charge dominated multi-turn transport will also be presented.

 
TUPAS048 Beam Extraction Concepts and Design for the University of Maryland Electron Ring (UMER) 1754
 
  • M. Walter, G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, T. F. Godlove, I. Haber, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, C. Wu
    UMD, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.

The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron storage ring has been closed and recent operations have been focused on achieving multi-turn transport. An entire suite of terminal diagnostics is available for time-resolved phase space measurements of the beam. These diagnostics have been mounted and tested at several points on the ring before it was closed. UMER utilizes a unique injection scheme which uses the fringe fields of an offset quadrupole to assist a pulsed dipole in bending the beam into the ring. Similar concepts, along with more traditional electrostatic methods, are being considered for beam extraction. This presentation will focus on the recent efforts to design and deploy these major subsystems required for beam extraction.

 
THPAS032 Modeling Skew Quadrupole Effects on the UMER Beam 3567
 
  • C. Papadopoulos, G. Bai, B. L. Beaudoin, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, M. Walter
    UMD, College Park, Maryland
 
  Funding: US Department of Energy

This is a numerical study of the effects of skew quadrupoles on the beam used in University of Maryland Electron Ring (UMER). As this beam is space-charge dominated, we expect new phenomena to be present compared to the emittance-dominated case. In our studies we find that skew quadrupoles can severely affect the halo of the beam and cause emittance growth, even in the first turn of the beam. For our simulations we used the WARP particle-in-cell code and we compared the results with the experimental study of skew quadrupole effects (to be reported separately).

 
THPAS033 Evolution of Laser Induced Perturbation and Experimental Observation of Space Charge Waves in the University of Maryland Electron Ring (UMER) 3570
 
  • J. C.T. Thangaraj, G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, K. Tian, M. Walter
    UMD, College Park, Maryland
 
  Funding: This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855

The University of Maryland Electron Ring (UMER) is a scaled model to investigate the transverse and longitudinal physics of space charge dominated beams. It uses a 10-keV electron beam along with other scaled beam parameters that model the larger machines but at a lower cost. Understanding collective behavior of intense, charged particle beams due to their space charge effects is crucial for advanced accelerator research and applications. This paper presents the experimental study of longitudinal dynamics of an initial density modulation on a spacecharge dominated beam. A novel experimental technique of producing a perturbation using a laser is discussed. Using a laser to produce a perturbation provides the ability to launch a pure density modulation and to have better control over the amount of perturbation introduced. Collective effects like space charge waves and its propagation over long distances in a quadrupole channel are studied. One dimensional cold fluid model is used for theoretical analysis and simulations are carried out in WARP-RZ.

 
THPAS034 Fast Imaging of Time-dependent Distributions of Intense Electron Beams 3573
 
  • K. Tian, G. Bai, B. L. Beaudoin, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, M. Walter, C. Wu
    UMD, College Park, Maryland
 
  Funding: Work supported by the U. S. Department of Energy, the Office of Naval Research and the Joint Technology Office

Longitudinal perturbations can be generated in the space-charge dominated regimes in which most beams of interest are born. To study the modification of transverse beam distributions by longitudinal beam dynamics, we have conducted experimental studies using low energy electron beams by taking time resolved images of a beam with longitudinal density perturbations. Two different diagnostics are used: optical transition radiation (OTR) produced from an intercepting silicon based aluminum screen and a fast (<5ns decay time) phosphor screen. It is found that the beam is significantly affected by the perturbation. However the OTR signal is very weak and requires over 45 minutes of frame integration. The fast phosphor screen has much better sensitivity (~1'000 times enhancement). In this paper, we also report on the time resolved measurement of a parabolic beam, showing interesting correlations between transverse and longitudinal distributions of the beam.