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Fiorito, R. B.

Paper Title Page
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.

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WEZC01 Phase Space Tomography of Beams with Extreme Space Charge 2025
  • D. Stratakis, S. Bernal, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, J. C.T. Thangaraj, K. Tian, M. Walter
    UMD, College Park, Maryland
  Funding: This work is funded by US Dept. of Energy grant numbers DE-FG02-94ER40855 and DE-FG02-92ER54178, and the office of Naval Research grant N00014-02-1-0914.

A common challenge for accelerator systems is to maintain beam quality and brightness over the usually long distance from the source to the target. In order to do so, knowledge of the beam distribution in both configuration and velocity space along the beam line is needed. However, measurement of the velocity distribution can be difficult, especially for beams with strong space charge. Here we present a simple and portable tomographic method to map the beam phase space, which can be used in the majority of accelerators. The tomographic reconstruction process has first been compared with results from simulations using the particle-in-cell code WARP. Results show excellent agreement even for beams with extreme space charge and exotic distributions. Our diagnostic has also been successfully demonstrated experimentally on the University of Maryland Electron Ring, a compact ring designed to study the transverse dynamics of beams in both emittance and space charge dominated regimes. Special emphasis is given to intense beams where our phase space tomography diagnostic is used to shed light on the consequences of the space charge forces on the transport of these beams.

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THOAC04 RMS Emittance Measurements Using Optical Transition Radiation Interferometry at the Jefferson Lab FEL 2645
  • M. A. Holloway, R. B. Fiorito, P. G. O'Shea, A. G. Shkvarunets
    UMD, College Park, Maryland
  • S. V. Benson, W. Brock, J. L. Coleman, D. Douglas, R. Evans, P. Evtushenko, K. Jordan, D. W. Sexton
    Jefferson Lab, Newport News, Virginia
  Funding: Office of Naval Research Joint Technology Office

Optical Transition Radiation Interferometry (OTRI) has proven to be effective tool for measuring rms beam divergence. We present rms emittance measurement results of the 115 MeV energy recovery linac at the Thomas Jefferson National Laboratories Free electron Laser using OTRI. OTRI data from both near field beam images and far field angular distribution images give evidence of two spatial and angular distributions within the beam. Using the unique features of OTRI we segregate the two distributions of the beam and estimate separate rms emittance values for each component.

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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.

FRPMS033 OTR Measurements of the 10 keV Electron Beam at the University of Maryland Electron Ring (UMER) 4006
  • R. B. Fiorito, B. L. Beaudoin, S. J. Casey, D. W. Feldman, P. G. O'Shea, B. Quinn, A. G. Shkvarunets
    UMD, College Park, Maryland
  Funding: Research supported by Office of Naval Research, Joint Technology Office, and the Department of Energy

We present strong evidence of the observation of optical transition radiation (OTR) from aluminized silicon targets intercepting the UMER 10 keV, 100 ns pulsed electron beam, using fast (300ps and 1ns rise time) photomultiplier tubes. An intensified gated (3ns-1ms) CCD camera is used to image the beam using OTR and to study its time evolution throughout the beam pulse. A comparison of wave forms and time resolved OTR images is presented along with time integrated images obtained with phosphor screens for different initial conditions, i.e. beam currents and gun bias voltages.

correspondance email: rfiorito@umd.edu

FRPMS034 Optical Diffraction-Dielectric Foil Radiation Interferometry Diagnostic for Low Energy Electron Beams 4012
  • A. G. Shkvarunets, R. B. Fiorito, P. G. O'Shea
    UMD, College Park, Maryland
  • M. E. Conde, W. Gai, J. G. Power
    ANL, Argonne, Illinois
  Funding: ONR and the DOD/Joint Technology Office

We have developed a new optical diffraction radiation (ODR) - dielectric foil radiation interferometer to measure the divergence of the low energy (8 - 14 MeV) ANL - Advanced Wakefield Accelerator electron beam. The interferometer employs an electro-formed micromesh first foil, which overcomes the inherent scattering limitation in the solid first foil of a conventional OTR interferometer, and an optically transparent second foil. The interference of forward directed ODR from the mesh and optical radiation from the dielectric foil is observed in transmission. This geometry allows a small gap between the foils (1 - 2 mm), which is required to observe fringes from two foils at low beam energies. Our measurements indicate that a single Gaussian distribution is sufficient to fit the data.

correspondance email: shkvar@umd.edu