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Pulse shape and spectrum of coherent diffraction-limited transition radiation from electron beams

Description: The electric field in the temporal and spectral domain of coherent diffraction-limited transition radiation is studied. An electron bunch, with arbitrary longitudinal momentum distribution, propagating at normal incidence to a sharp metal-vacuum boundary with finite transverse dimension is considered. A general expression for the spatiotemporal electric field of the transition radiation is derived, and closed-form solutions for several special cases are given. The influence of parameters such as radial boundary size, electron momentum distribution, and angle of observation on the waveform (e.g., radiation pulse length and amplitude) are discussed. For a Gaussian electron bunch, the coherent radiation waveform is shown to have a single-cycle profile. Application to a novel THz source based on a laser-driven accelerator is discussed.
Date: December 20, 2003
Creator: van Tilborg, J.; Schroeder, C.B.; Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Long wavelength end-effect undulator radiation (Transition Undulator Radiation)

Description: As first pointed out by K.-J. Kim, undulator radiation contains a broad-band component in the long wavelength region. This radiation is due to the change in longitudinal velocity of an electron upon entering and leaving an undulator. The radiation pattern is a hollow cone, peaked in the forward direction, with an opening angle of approximately 1/{gamma}, with a spectrum covering a wide range, including the infra-red and the visible. The radiation is radially polarized, analogous to transition radiation, and exhibits interference effects between the entrance and exit ends of the undulator, similar to the interference effects observed for transition radiation from a thin slab of material. A straightforward application of formulas from Jackson ({ital Classical Electrodynamics}) results in a closed form exact expression for the low frequency limit of this novel radiation effect, Transition Undulator Radiation or TUR. 3 refs., 3 figs.
Date: January 29, 1996
Creator: Kincaid, B.M.
Partner: UNT Libraries Government Documents Department

Final Report for DOE Grant No. DE-FG02-02ER83460

Description: The goals of the phase I program were to enhance the software package ''CyberRay'' as follows: (1) Incorporate a particle-in-cell space charge model; (2) Incorporate a model for transition radiation; (3) Develop versions for both Microsoft Windows and Macintosh OS X operating systems; and (4) Incorporate support for dual processors. The program was very successful. The space charge model, transition radiation model, and support for two operating systems were fully implemented resulting in a unique product useful to both the accelerator and laser communities. Support for dual processors was not implemented during the phase I program due to lack of time. In what follows the enhanced CyberRay package is described in detail.
Date: April 21, 2003
Creator: Gordon, Daniel & Hafizi, Bahman
Partner: UNT Libraries Government Documents Department

Observation of coherent transition radiation at the Accelerator Test Facility

Description: Transition radiation is emitted when a relativistic, charged particle passes between media with different dielectric constants. Most often the transition is between vacuum and a conductor. The transition radiation spectrum theoretically extends from DC to extremely short wavelengths determined by the particle energy. In practice, the long wavelengths are cut off in the millimeter or centimeter range by the shielding effect of the vacuum chamber containing the particles. This report briefly discusses this experiment and some observations.
Date: January 1, 1996
Creator: Blum, E.B.
Partner: UNT Libraries Government Documents Department

Diffraction effects in the coherent transition radiation bunch length diagnostics

Description: Diffraction effects in the Coherent Transition Radiation (CTR) bunch length diagnostics are considered for the A0 Photoinjector and the New Muon Laboratory (NML) injection module. The effects can cause a noticeable distortion of the measured CTR spectra depending on the experimental setup and the bunch parameters and resulting in errors of the bunch length measurements. Presented calculations show possible systematic errors in the bunch length in measurements based on the CTR spectra at A0 Photo injector and the NML injection module.
Date: August 1, 2007
Creator: Kazakevich, G.; Lebedev, V.; Nagaitsev, S. & /Fermilab
Partner: UNT Libraries Government Documents Department

Proof-Of-Principle Experiment for Laser-Driven Acceleration of Relativistic Electrons in a Semi-Infinite Vacuum

Description: We recently achieved the first experimental observation of laser-driven particle acceleration of relativistic electrons from a single Gaussian near-infrared laser beam in a semi-infinite vacuum. This article presents an in-depth account of key aspects of the experiment. An analysis of the transverse and longitudinal forces acting on the electron beam is included. A comparison of the observed data to the acceleration viewed as an inverse transition radiation process is presented. This is followed by a detailed description of the components of the experiment and a discussion of future measurements.
Date: March 1, 2006
Creator: Plettner, T.; Byer, R.L.; /Stanford U., Phys. Dept.; Colby, E.; Cowan, B.; Sears, C.M.S. et al.
Partner: UNT Libraries Government Documents Department


Description: Traditionally, thin metal foils are employed for optical transition radiation (OTR) beam diagnostics but the possibility of shorting accelerator insulating surfaces and modifying accelerating fields are concerns. The successful utilization of dielectric foils in place of metal ones could alleviate these issues but necessitates more understanding of the OTR data for inferring desired beam parameters because of the dielectric's finite permittivity. Additionally, the temperature dependence of the relevant foil parameters due to beam heating should be accounted for. Here, we present and discuss sample synthetic diagnostic results of Kapton OTR spot-size measurements from the Flash X-Ray (FXR) accelerator which studies these and sightline effects. These simulations show that in some cases, the observed spot-sizes and radii are noticeably larger than the beam radii.
Date: June 13, 2007
Creator: Tang, V; Brown, C & Houck, T
Partner: UNT Libraries Government Documents Department

Progress on the Flash X-Ray Optical Transition Radiation Diagnostic

Description: This document summarizes the Flash X-Ray accelerator (FXR) optical transition radiation (OTR) spot-size diagnostics efforts in FY07. During this year, new analysis, simulation, and experimental approaches were utilized to interpret OTR spot data from both dielectric foils such as Kapton (VN type) and metal coated foils. Significant new findings of the intricacies involved in the diagnostic and of FXR operational issues were achieved. Geometry and temperature based effects were found to affect the beam image profiles from the OTR foils. These effects must be taken into account in order to deduce accurately the beam current density profile.
Date: March 30, 2008
Creator: Tang, V; Houck, T & Brown, C
Partner: UNT Libraries Government Documents Department

Longitudinal electron bunch diagnostics using coherent transition radiation

Description: The longitudinal charge distribution of electron bunches in the Fermilab/Nicadd A0 photoinjector was determined using the coherent transition radiation produced by electrons passing through a thin metallic foil. The autocorrelation of the transition radiation signal was measured with a Michelson-type interferometer. The response function of the interferometer was determined from measured and simulated power spectra for low electron bunch charge and maximum longitudinal compression. A Kramers-Kronig technique was used to determine longitudinal charge distribution. Measurements were performed for electron bunch lengths in the range from 0.3 to 2 ps (rms).
Date: May 1, 2005
Creator: Mihalcea, D.; Bohn, C.L.; U., /Northern Illinois; Happek, U.; U., /Georgia; Piot, P. et al.
Partner: UNT Libraries Government Documents Department

Coherent Transition Radiation to Measure the SLAC Electron Bunch Length

Description: Coherent transition radiation is used to measure the length of the ultra-short electron bunches available at the Stanford Linear Accelerator Center. The results and the limitations of the method are described.
Date: May 13, 2005
Creator: Muggli, P.; U., /Southern California; Hogan, M.J.; Barnes, C.D.; Walz, D.; Krejcik, P. et al.
Partner: UNT Libraries Government Documents Department

Analysis of Laser Acceleration in a Semi-infinite Space as Inverse Transition Radiation

Description: This article calculates the energy gain of a single relativistic electron interacting with a single gaussian beam that is terminated by a metallic reflector at normal incidence by two different methods: the electric field integral along the path of the electron, and the overlap integral of the transition radiation pattern from the conductive foil with the laser beam. It is shown that for this instance the two calculation methods yield the same expression for the expected energy change of the electron.
Date: October 26, 2005
Creator: Plettner, T.
Partner: UNT Libraries Government Documents Department

High power beam profile monitor with optical transition radiation

Description: A simple monitor has been built to measure the profile of the high power beam (800 kW) delivered by the CEBAF accelerator at Jefferson Lab. The monitor uses the optical part of the forward transition radiation emitted from a thin carbon foil. The small beam size to be measured, about 100 {mu}m, is challenging not only for the power density involved but also for the resolution the instrument must achieve. An important part of the beam instrumentation community believes the radiation being emitted into a cone of characteristic angle 1/{gamma} is originated from a region of transverse dimension roughly {lambda}{gamma}; thus the apparent size of the source of transition radiation would become very large for highly relativistic particles. This monitor measures 100 {mu}m beam sizes that are much smaller than the 3.2 mm {lambda}{gamma} limit; it confirms the statement of Rule and Fiorito that optical transition radiation can be used to image small beams at high energy. The present paper describes the instrument and its performance. The authors tested the foil in, up to 180 {mu}A of CW beam without causing noticeable beam loss, even at 800 MeV, the lowest CEBAF energy.
Date: June 1, 1997
Creator: Denard, J.C.; Piot, P.; Capek, K. & Feldl, E.
Partner: UNT Libraries Government Documents Department

Measuring and Controlling Energy Spread in CEBAF

Description: As compared to the electron storage rings, one advantage of recirculating linacs is that the beam properties at a target are no longer dominated by the equilibrium between quantum radiative diffusion and radiation damping because new beam is continually injected into the accelerator. This allows the energy spread from a CEBAF-type machine to be relatively small; the measured energy spread from CEBAF at 4 GeV is less than 100 parts per million accumulated over times of order several days. In this paper, the various subsystems contributing to the energy spread of a CEBAF-type accelerators are reviewed, as well as the machine diagnostics and controls that are used in CEBAF to ensure that a small energy spread is provided during routine running. Examples of relevant developments are (1) stable short bunches emerging from the injector, (2) precision timing and phasing of the linacs with respect to the centroid of the beam bunches on all passes, (3) implementing 2 kHz sampling rate feedback systems for final energy stabilization, and (4) continuous beam energy spread monitoring with optical transition radiation devices. We present measurement results showing that small energy spreads are achieved over extended periods.
Date: August 1, 2000
Creator: Krafft, G.; Denard, J.-C.; Dickson, R.; Kazimi, R.; Lebedev, V. & M.Tiefenback
Partner: UNT Libraries Government Documents Department

Transition undulator radiation as bright infrared sources

Description: Undulator radiation contains, in addition to the usual component with narrow spectral features, a broad-band component in the low frequency region emitted in the near forward direction, peaked at an angle 1/{gamma}, where {gamma} is the relativistic factor. This component is referred to as the transition undulator radiation, as it is caused by the sudden change in the electron`s longitudinal velocity as it enters and leaves the undulator. The characteristics of the transition undulator radiation are analyzed and compared with the infrared radiation from the usual undulator harmonics and from bending magnets.
Date: December 1, 1994
Creator: Kim, Kwang-Je
Partner: UNT Libraries Government Documents Department

Beam Profile Measurement at 30 GeV Using Optical Transition Radiation

Description: We present results of measurements of spot size and angular divergence of a 30 GeV electron beam through use of optical transition radiation (OTR). The OTR near field pattern and far field distribution are measured as a function of beam spot size and divergence at wavelengths of 441, 532, and 800 nm, for both the single and double foil configurations. Electron beam spot sizes of 50 {micro}m rms have been resolved, demonstrating the utility of OTR for measurement of small beam spot sizes of high energy (30 GeV) electron beams. Two-foil interference was clearly observed and utilized electron beam angular divergences of {approximately} 100 {micro}rad.
Date: July 10, 1999
Creator: Whittum, David H
Partner: UNT Libraries Government Documents Department

Implementation of improved interactive image analysis at the Advanced Photon Source (APC) linac.

Description: An image-analysis system, based on commercially available data visualization software (IDL [1]), allows convenient interaction with image data while still providing calculated beam parameters at a rate of up to 2 Hz. Image data are transferred from the IOC to the workstation via EPICS [2] channel access. A custom EPICS record was created in order to overcome the channel access limit of 16k bytes per array. The user can conveniently calibrate optical transition radiation (OTR) and fluorescent screens, capture background images, acquire and average a series of images, and specify several other filtering and viewing options. The images can be saved in either IDL format or APS-standard format (SDDS [3]), allowing for rapid postprocessing of image data by numerous other software tools.
Date: September 11, 1998
Creator: Arnold, N.
Partner: UNT Libraries Government Documents Department

Observations of z-dependent microbunching harmonic intensities using COTR in a SASE FEL.

Description: The nonlinear generation of harmonics in a self-amplified spontaneous emission (SASE) free-electron laser (FEL) continues to be of interest. Complementary to such studies is the search for information on the electron beam microbunching harmonic components, which are revealed by coherent optical transition radiation (COTR) experiments. An initial z-dependent set of data has been obtained with the fundamental at 530 nm and the second harmonic at 265 nm. The latter data were collected after every other undulator in a nine-undulator string. These results are compared to estimates based on GINGER and an analytical model for nonlinear harmonic generation.
Date: September 24, 2002
Creator: Lumpkin, A. H.; Biedron, S. G.; Dejus, R. J.; Berg, W. J.; Borland, M.; Chae, Y. C. et al.
Partner: UNT Libraries Government Documents Department

Evidence for transverse dependencies in COTR and microbunching in a SASE FEL.

Description: Using coherent optical transition radiation (COTR) techniques, we have observed transverse dependencies, which in some aspects relate to the electron beam microbunching in a visible wavelength (540 nm) self-amplified spontaneous emission (SASE) free-electron laser (FEL). The experimental COTR observations include the z-dependent e-beam sizes, the z-dependent angular distributions, and the z-dependent spectra (which show an x-dependence). A 30-40% narrowing of the observed beam size using COTR is explainable by the mechanism's dependence on the square of the number of microbunched particles. However, additional effects are needed to explain beam size reductions by factors of 2-3 at different z locations. Localized e-beam structure in the gun or induced in the bunch compression process may result in microbunching transverse dependence, and hence the observed COTR effects.
Date: September 24, 2002
Creator: Lumpkin, A. H.; Chae, Y. C.; Lewellen, J. W.; Berg, W. J.; Borland, M.; Biedron, S. G. et al.
Partner: UNT Libraries Government Documents Department

Feasibility of OTR imaging of non-relativistic ions at GSI

Description: The feasibility of using the optical transition radiation (OTR) generated as a 11.4- to 300-MeV/u ion beam passes through a single metal conducting plane for a minimally intercepting beam profile monitor for GSI/Darmstadt has been evaluated for the first time. Although these are non-relativistic beams, their beta and gamma values are similar to the 80-keV electron-beam imaging studies previously done on the CTF3 injector. With anticipated beam intensities of 10{sup 9} to 10{sup 11} particles per pulse and the predicted charge-squared dependence of OTR, the ion charge state becomes a critical factor for photon production. The OTR signal from the ion charge integrated over the video field time should be comparable to or larger than the CTF3 electron case. These signal strengths will allow a series of experiments to be done that should further elucidate the working regime of this technique.
Date: March 1, 2011
Creator: Lumpkin, A.H.
Partner: UNT Libraries Government Documents Department

Single-shot electro-optic sampling of coherent transition radiation at the A0 Photoinjector

Description: Future collider applications and present high-gradient laser plasma wakefield accelerators operating with picosecond bunch durations place a higher demand on the time resolution of bunch distribution diagnostics. This demand has led to significant advancements in the field of electro-optic sampling over the past ten years. These methods allow the probing of diagnostic light such as coherent transition radiation or the bunch wakefields with sub-picosecond time resolution. Potential applications in shot-to-shot, non-interceptive diagnostics continue to be pursued for live beam monitoring of collider and pump-probe experiments. Related to our developing work with electro-optic imaging, we present results on single-shot electro-optic sampling of the coherent transition radiation from bunches generated at the A0 photoinjector.
Date: August 1, 2011
Creator: Maxwell, T. J.; Ruan, J.; Piot, P. & Thurman-Keup, R.
Partner: UNT Libraries Government Documents Department

Multi Optical Transition Radiation System for ATF2

Description: In this paper we describe the design, installation and first calibration tests of a Multi Optical Transition Radiation System in the beam diagnostic section of the Extraction (EXT) line of ATF2, close to the multi wire scanner system. This system will be a valuable tool for measuring beam sizes and emittances coming from the ATF Damping Ring. With an optical resolution of about 2 {micro}m an original OTR design (OTR1X) located after the septum at the entrance of the EXT line demonstrated the ability to measure a 5.5 {micro}m beam size in one beam pulse and to take many fast measurements. This gives the OTR the ability to measure the beam emittance with high statistics, giving a low error and a good understanding of emittance jitter. Furthermore the nearby wire scanners will be a definitive test of the OTR as a beam emittance diagnostic device. The multi-OTR system design proposed here is based on the existing OTR1X.
Date: July 13, 2012
Creator: Alabau-Gonzalvo, Javier; /Valencia U., IFIC; Blanch Gutierrez, Cesar; /Valencia U., IFIC; Civera, Jose Vicente; /Valencia U., IFIC et al.
Partner: UNT Libraries Government Documents Department