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Presentation Instructions
AAC'04 Agenda
AAC'04 Poster
Organizing Committee
Workshop Working Groups


















Diagnostics, Control and Synchronization
Feng Zhou: Transverse phase-space measurements at a magnetic bunch compressor at the BNL-ATF
  Significantly created Coherent Synchrotron Radiation (CSR) in a magnetic bunch compressor may distort both the longitudinal and transverse phase spaces. A tomography technique [V. Yakimenko, et al., PRST-AB, No. 12, 2003) is employed at BNL-ATF to measure the real transverse phase spaces at a bunch compressor. Complete measurements at different beam conditions are proposed. Preliminary data is presented.
Robert England: UCLA Neptune Ramped Electron Bunch Experiment
  A ramped electron bunch (i.e. one having a current density which rises linearly from the head to the tail and then drops sharply to zero) has been predicted to be an ideal drive beam for the plasma wake field accelerator due to the large transformer ratio it is capable of generating. A scheme was recently proposed for the creation of a relativistic electron bunch that approximates a ramped current profile [England, et al., AIP Conf. Proc. 647, p.884 (2002)], using a dogleg or dispersionless translating section as a bunch compressor. An experiment is underway at the Neptune laboratory using this scheme to create such a beam. The diagnostic being developed for measuring the temporal profile of the beam is an X-Band transverse deflecting mode cavity.
Dennis Palmer: The ORION Photoinjetcor
  The ORION Photoinjector will replace the themonic DC gun presently used as the electron source at the Next Linear Collider Test Accelerator (NLCTA). The ORION Photoinjector is comprised of following subsystems: RF Gun, Emittance Compensation Magnet, UV Drive Laser, High Power RF Waveguide, and Diagnostics Subsystems. The initial use of the ORION Photoinjector is to support the approved experiment, E-163, a demonstration experiment of laser acceleration at 800 nm with 5 pC of bunch charge. In addition, the ORION Photoinjector must support the NLCTA X-Band structure development program, which requires 1 nC of charge.The RF gun is an S-Band (2856 GHz) 1.6 cell standing wave structure with a removable cathode plate. A single solenoid magnet is used for emittance compensation. A commercial solid state diode pumped Tsunami-Spitfire-HPR, oscillator-amplifier subsystem, is used to generate 2.3 mJ of IR energy at a reparation rate of 1 KHz. The photocathode is illuminated with 266 nm UV laser is generated for an x3 harmonic triple plate. These laser components were procured for the Spectra Physics laser company. The high power waveguide subsystem is a totally ultra high vacuum (UHV), centered around a -3dB coupler. This coupler is used to protect the 5045 klystron from reflected RF energy from the standing wave 1.6 cell RF gun and is also used as a diagnostics port for in situ low power RF gun tuning. The diagnostics subsystem is centered between the emittance compensation magnet and two 0.9 m X-Band (11.424 GHz) acceleration section. Beam energy, emittance, spot size and charge are measured at a pulse to pulse 10Hz repetition rate. UHV isolation and beam steering is also accounted for in this area.In this paper we will report on the status and experimental results of each subsystem. For more information of the ORION Center and Facilities please refer tohttp://www-project.slac.stanford.edu/orion
Gil Travish: A PMQ-based, Ultra-short Focal Length, Final Focus System for Next Generation Beam-Radiation and Beam-Plasma Experiments
  Next-generation advanced-accelerators such as the PWFA, and beam-radiation interactions such as inverse-Compton scattering, depend on increased beam-density to achieve superior results. The photoinjector has enabled the production of high-brightness beams that are desirable for experiments with critical dependencies on bunch length and emittance. Along with the production of shorter and lower-emittance beams, comes the need to produce shorter focal-lengths (beta-functions). An approach to creating strong focusing-channels using high field, small-bore permanent-magnet quadrupoles (PMQs) has been followed by the authors. A focusing system using three PMQs, each composed of 16 Nd-Fe-B sectors in a Halbach geometry has been installed in the PLEIADES inverse-Compton experiment. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis. This presentation covers the details of the focusing system, experimental experience, and implications for future experiments with an emphasis on advanced accelerators.
Stanislav Zhilkov: Sequence of THz pulses as a tool for plasma diagnostics
  Characterization of small non-stationary plasma formations by electromagnetic waves has both hardware and software challenges. Particularly, when the homogeneous density with 1mm-scale domains are on the order of 1mm, the time variation in the medium properties becomes significant. To penetrate through plasma formations and have necessary space resolution, the probing field frequency must be in the THz range. And to follow the plasma evolution, the field characteristics should be modulated in comparable time scales. A compact SP-FEL THz CW source has been developed at Dartmouth [1]. This source can be modified to provide high-rate amplitude modulation, as recently proposed [2], to achieve the necessary probe field characteristics. Experimentally, the diffracted field from the plasma formation is measured. The plasma characteristics can then be inferred through an inverse diffraction analysis based on a method of integral equations [3]. The efficacy of this approach for studying fast time variation of millimeter features in plasmas will be discussed. References1. J.E. Walsh, J.H. Brownell, J.C. Swartz, J. Urata, and M.F. Kimmitt, Nucl. Instrum. & Meth. A 429, 457 (1999).2. Zhilkov S, US Pat. Appl. No. 60/429,203 filed 11/26/2002; Zhilkov S and Friedman G, Abstract 270 in ICOPS-04 (Baltimore MD, June 2004), published by IEEE, 2004.3. Aleksandrova A, Khizhnyak N. Boundary-value problems of magnetic hydrodynamics, published by Test-Radio, Kharkov, Ukraine, 1993, 230 pages (in Russian); Nerukh A, Scherbatko I, Marciniak M. Electromagnetics of Modulated Medium with Applications to Photonics; published by Nation. Institute of Telecommunications, Warsaw, Poland, 2001; Zhilkov S, Nerukh A, Sakhnenko N, Aleksandrova A. Abstract 439 in ICOPS-04 (Baltimore MD, June 2004), published by IEEE, 2004.
Jin-Soo Kim: Design of standing-wave mutli-cavity beam-monitor for simultaneous beam position and emittance measurements
  Beam position and emittance are critical parameters for accelerator applications including colliders and radiation generation, as in free-electron lasers. A high precision emittance measurement requires precise beam position at the measurement location. At present there is no existing technique, commercial or otherwise, for non-destructive pulse-to-pulse simultaneous beam position and emittance measurement.FAR-TECH, Inc. is currently developing a high precision cavity-based beam monitor for simultaneous beam position and emittance measurements pulse-to-pulse, without beam interception and without moving parts. The design and anlysis of a multi-cavity standing wave structure, in which the quadrupole and the dipole standing wave modes resonate at harmonics of the beam operating frequency, for a pulse-to-pulse emittance measurement system will be presented. Specifically, we will present the initial design and anlysis of an optimized 9-cavity standing wave beam monitor for the Next Linear Collider(NLC). The quadrupole field of the monitor operates at the pi-mode resonating at 11.424GHz, the 16th harmonic of the NLC bunch frequency, and the 3pi/4 dipole mode at 8.568GHz, the 12th harmonic.

Acknowledgement: S. Barry, R. Jones, A. Weidemann.

*Work supported by SBIR grant # DE-FG02-03ER83658

Khalid Chouffani: Determination of Electron Beam Parameters by Means of Laser-Compton Scattering
  Laser-Compton scattering (LCS) is not only viewed as a bright, tunable and quasi-monochromatic X-ray source [1] but also as a non-intercepting electron beam monitor [2]. LCS X-rays peak energy and FWHM depend strongly on the characteristics of the electron beam, such as electron beam energy, angular and energy spread, and angle with respect to detection direction. LCS experiments were carried out at the Idaho Accelerator Center (ICA) using a 20-22 MeV, 5 ns long electron beam. The electron beam was brought to an approximate head-on collision with a high power Nd:YAG laser. We observed clear, intense and narrow LCS X-ray spectral peaks resulting from the interaction of the electron beam with the 532 nm Nd:YAG laser second harmonic. The laser pulse energy and pulse length at 532 was 0.25 J and 7 ns respectively. The LCS x-ray energy lines and widths were measured as a function of the electron beam energy and energy-spread respectively. The results recorded showed good agreement with the predicted values. LCS measurements, which include angular distribution measurements, show that LCS can provide information on the electron beam pulse length, direction, energy, angular and energy spread.

[1] F. Carroll in: Proceedings of the workshop on Medical and Biological Imaging with Novel X-ray beams, Idaho Accelerator Center, Pocatello, ID, USA, 7-8 August 2003.[2] W. P. Leemans et al., Phys. Rev. Lett. 77 (1996) 4182.

J. Douglas Gilpatrick: Wide Dynamic Range Beam Diagnostics Measurements for Ion Accelerators
  As light- and heavy-ion accelerator technology progresses, there will be a further demand for charged particle beam instrumentation to measure beam parameters over a very wide dynamic range. There are several different ways to express a beam diagnostic instrument’s ability to measure the beam’s characteristics over a wide dynamic range. For example, presently beam profiles are measured over current ranges of 1 to 100 mA (in the case of the Low Energy Demonstration Accelerator) or 1 to 20 mA in the case of the Los Alamos Neutron Science Center facility. The beam current dynamic range requirements are based on the facilities users’ needs and the facilities ability to tune the associated accelerators and beamlines. However, as peak beam currents requirements rise, the beam’s halo may be lost to beam line components during tuning and operation facility conditions resulting in unwanted beam pipe radioactivation. To minimize these lost beam debilitating effects, future beam profile measurements will need to measure further out in the beam distributions, i.e., driving the needs for beam profile measurement to be measured over greater dynamic ranges. Finally, future ion accelerator facilities will require measuring all beam diagnostics parameters over a large variety of charge-to-mass ratios and experimenter delivered beam current requirements. These new additional requirements will drive beam profiles to be acquired over at least a 1000:1 peak current ratio. This presentation will discuss the present typical dynamic ranges for such common beam measurements, such as beam position and profiles and provide examples of future wide dynamic range beam measurements.
Steve Korbly: A Smith-Purcell Radiation Bunch Length Diagnostic
  A Smith-Purcell radiation diagnostic to measure the micro bunch length of a 20MeV, 17 GHz electron bunch train is being tested at MIT. The bunch length can be determined by measuring the frequency and angular distribution of the emitted radiation. The beam is produced by a 17 GHz, 50 MeV/m traveling wave accelerator built by Haimson Research Corporation (HRC). The high operating frequency of this accelerator allows for the production of ultra-short electron bunches of about 180 femtoseconds. We will present an update on the progress of the experiment and initial results.
Pierre MICHEL: Thomson scattering from laser wakefield accelerators
  The production of ultrashort (fs) X-ray pulses from Thomson scattering of high power laser pulses off relativistic electrons bunches produced by plasma-based accelerators is discussed. The electron bunches are produced with either a self-modulated laser wakefield accelerator (SM-LWFA) or through a standard laser wakefield accelerator (LWFA) with optical injection. For a SM-LWFA, the electron bunch has a high charge with a broad energy distribution, resulting in X-ray pulses with high flux and a broadband spectrum. For a LWFA with optical injection, the electron bunch can be ultrashort (fs) with a narrow energy distribution, resulting in an ultrashort X-ray pulse with a nearly monochromatic spectrum. Nonlinear Thomson scattering (high laser intensity) will be considered, as well as the effects of the laser pulse profile. Thomson scattering may provide a useful diagnostic for determining the electron bunch properties via the scattering X-ray spectrum.This work is supported by DoE, DE-AC03-76SF0098.
Tomas Plettner: Diagnostics and controls in the LEAP experiment
  The objective of the LEAP experiment is to observe laser driven particle acceleration in vacuum from a single interaction between a relativistic electron beam and a linearly polarized ultra short near-infrared laser. The challenges in this experiment include the manipulation, detection and characterization of individual electron bunches, diagnostics for spatial overlap between the laser and the electron beam at the accelerator cell location and the development of an automated data acquisition and instrument control software. Still, by far the most difficult challenge has proven to be a high resolution absolute timing diagnostic between the laser and the electron beam.

  In previous years we have implemented a streak camera based timing diagnostic that observed the laser radiation from the accelerator cell co propagated with the Cherenkov radiation produced by the electron beam downstream in a Cherenkov cell immediately of the accelerator cell. Problems with the low photon yield of the Cherenkov cell, the dispersion of the Streak camera optics and the electronics limited us to a resolution of several tens of psec.

  Implementation of a better streak camera model as well as improvements in the Cherenkov cell will greatly improve our timing resolution. Furthermore, we are placing an IFEL immediately upstream of the accelerator cell, which will allows us to detect the absolute timing between the laser and the electron beam to within a psec.

  We expect that the improvements in the laser timing monitors combined with the completely redesigned accelerator cell will greatly enhance our probability of succeeding with our goal of observing laser driven particle acceleration.

Sergey Shchelkunov: A New Nondestructive Method for Measuring the RMS Length of Charge Bunches Using Their Wake Field Radiation Spectrum
  We report progress in the development of a nondestructive technique to measure bunch rms-length in the psec range and below, and eventually in the fsec range, by measuring the high- frequency spectrum of wake field radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. We demonstrate both experimentally and numerically that the generated spectrum is determined by the bunch rms-length, while the choice of the axial and longitudinal charge distribution is not important. Measurement of the millimeter-wave spectrum will determine the bunch rms-length in the psec range. This has been done using a series of calibrated mesh filters and the charge bunches produced by the 50MeV rf linac system at ATF, Brookhaven. We have developed the analysis of the factors crucial for achieving good accuracy in this measurement, and find the experimental data are fully understood by the theory. We also discuss the application of this technique for measuring fsec bunch lengths, using a prepared microstructure.
Jeroen van Tilborg: Coherent Transition Radiation From a Laser Wakefield Accelerator as an Electron Bunch Diagnostic
  We report on the observation and modeling of coherent transition radiation from femtosecond laser-accelerated electron bunches. The radiation, scaling quadratically with bunch charge, is generated as the electrons pass the plasma/vacuum boundary (transition radiation). Due to the limited transverse radius of the plasma boundary, diffraction effects will cause the angular distribution to open up and the total energy radiated is reduced with respect to an infinite boundary.The multi nanoCoulomb electron bunches, concentrated in a length of a few plasma periods (several tens of microns), experience partial charge neutralization while propagating inside the plasma towards the boundary. This reduces the space-charge blowout of the beam, allowing for coherent radiation at relatively high frequencies (several THz).The charge distribution of the electron bunch at the plasma/vacuum boundary can be derived from Fourier analysis of the coherent part of the transition radiation. An overview of several measurement techniques, designed for temporal and spectral characterization in the THz domain, will be given. Experimental results on transition radiation, such as energy, divergence, spectrum and polarization will be shown and correlated to electron beam properties.This work is performed under DOE-contract DE-AC-03-76SF0098.
Zikri Yusof: Schottky-Enabled Photoemission in a RF Accelerator Photoinjector - Possible Generation of Ultra-Low Transverse Thermal Emittance Electron Beam
  We present experimental evidence showing the clearest signature of the Schottky effect in a RF photoinjector using photons with energy lower than the Mg cathode work function. This signature is manifested by the shift in the RF phase angle for the onset of the detection of photoelectrons via single-photon absorption and presents a novel technique for a reasonable estimate of the field enhancement factor. By tuning the RF phase in the photoinjector to be close to the photoemission threshold condition, this becomes a viable method to generate an electron beam with very low thermal emittance and thus, a high brightness beam.
Yun Zou: Observation of Energy Equipartitioning in Low Energy Intense Electron Beam
  Characterization and possibly manipulation of the beam energy spread in space-charge dominated beam is an important aspect in the advanced accelerator concept. Many applications with intense charged particle beams, such as the ion drivers for Heavy Ion Fusion (HIF), require a small beam energy spread. It is believed that coupling between transverse and longitudinal direction due to intra beam scattering, instabilities and other mechanisms will cause an increase of the beam longitudinal energy spread. In order to understand the mechanism of the beam energy spread growth and therefore to control it, it is important to first be able to measure the beam energy spread with high precision. So far, little experiments have been done to investigate this problem in a systematic way. Low-energy, intense electron beams provide an economic way to study this problem in a small-scaled experimental setup. The results obtained with low-energy electron beams can be applied to high-energy, high-power beams with appropriate scaling. At the University of Maryland, experiments with space-charge dominated electron beams are being carried out to study the energy evolution in such beams. In order to measure the energy spread, a high-resolution retarding field energy analyzer has been developed and tested. A two-meter long linear system with solenoid focusing is being set up and commissioned. In this paper, we report some preliminary observations of the beam energy spread growth due to the equipartitioning process between the longitudinal and transverse direction. The initial experimental results are in remarkable good agreement with the lower limit of the beam energy spread set by the intra beam scattering theory. Under some other controlled conditions, energy spread larger than the predictions of the intra beam scattering theory are also observed.

* This work is sponsored by US Dept. of Energy.

Timur Shaftan: Characterization of bunch longitudinal properties with zero-phasing method
  We discuss the zero-phasing method as a powerful tool for studies of the electron bunch longitudinal phase space. General limitations of the resolution, including some of the modifications for the accuracy improvement, will be reviewed. As an illustration we present our recent experiments on characterization of the space-charge-induced modulation at DUV FEL.
Takahiro Watanabe: Angle and Length Measurements of Microbunches
  A simple beam angle measurement is being tested. The scheme, which is supposed to be employed as a monitor for pick-up of a single microbunch, is based on an observation of far-field Cherenkov radiation. Characteristics of the scheme, such as an angular resolution, have been investigated by numerical analysis and proof-of-principle experiments have been performed.Bunch length measurements of microbunches via coherent transition/diffraction radiation techniques are also planned. The availabilities and expected performances of a spectrometer and an interferometer for femosecond microbunches excited by IFEL have been estimated by numerical analysis.
Mitsuru Uesaka: Performance of synchronization and emittance of the Mg cathode photoinjector
  Mg cathode photoinjector of Spring8-U.Tokyo has been stably operating for three years mainly for radiation chemistry analysis. Generally a combination of the photocathode RF injector as a source of pump-beam and the femtosecond laser as one of probe-laser realizes this technique. Especially, the chemical reactions of hot, room temperature and critical water in a time-range of picosecond and sub-picosecond are very interesting phenomena. The important factor for such as the fast radiation chemistry is not only the pulse length of beam and laser but also the synchronization between the pump-beam and probe-laser.For the experiments of radiation chemistry, the photoinjector, in which the driven laser synchronized with the probe-laser illuminates the photo-cathode, is normally utilized with a accelerating structure and a magnetic bunch compressor such as chicane-type magnets. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picosecond, the instability of synchronization reduced the total time-resolution. The main source was not the synchronization of the driven- and probe-laser but that of laser and radio frequency. The stability of laser depends on environmental factors: The fluctuation of room temperature causes the instability. Now we have recognized that 0.5 degree (peak-to-peak) fluctuation of the laser-room temperature had approximately corresponded to the instability of 10 ps, since the crystal of Ti:Sapphire is very sensitive for the temperature. This timing-drift is a period of 1 hour roughly. Therefore, in order to reduce the temperature effect, we are constructing a new cooling system for the crystal. Continuous observation and analysis of the performance of the synchronization and emittance are reported. In addition, the YAG laser pumping the crystal in the regenerative amplifier will be replaced to the semiconductor laser.
Alex Lumpkin: Applications with Intense OTR Images: Microbunched Electron Beams*
  Coherent optical transition radiation (COTR) imaging techniques used for measuring the microbunching induced in the self-amplified spontaneous emission (SASE) free-electron laser (FEL) process have been very successful in the VUV-visible regime. Besides the fundamental link to the SASE mechanism, one of the significant advantages is the enhancement of the COTR strength by several orders of magnitude compared to the incoherent OTR process. This means that the standard imaging camera techniques can be employed as long as there are enough neutral density filters in place to keep the cameras out of saturation. This is not the modus operandi for OTR experiments with sub-nC-charge beams generally, but it can be for microbunched beams with bunching fractions of a few percent. In the case of the Advanced Photon Source (APS) SASE FEL, we have operated at wavelengths from 540 to 130 nm and observed the COTR z-dependent evolution easily. In addition, we have clearly demonstrated that COTR interferograms contain fundamental information about effective e-beam size and the critical e-beam/photon beam overlap that can be used on line to optimize gain.

* Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Alex Lumpkin: Applications with Intense OTR Images: 120-GeV Protons
  Although the optical transition radiation (OTR) mechanism has been used in many electron-beam imaging applications, proton-beam applications have been somewhat limited. One needs both a high charge intensity and a high-gamma beam so the OTR radiation cone can be collected with reasonable efficiency. In the case of the accelerator complex at Fermi National Accelerator Laboratory (FNAL), the Main Injector generates a 120-GeV proton beam with an intensity of 5 1012 for bombardment of the antiproton production target. This option satisfies both criteria, and the OTR is so bright that attenuation by 1000 with neutral density filters was needed to avoid saturating the CID camera when a 20-µm-thin Al foil was used as the converter screen. Based on this success, OTR stations are being planned for the antiproton transport line to the Tevatron to assist in evaluating the beam match and emittance. The ultimate goal is to improve the collider luminosity in Run II by optimizing the antiproton beam optics. Foil damage and radiation damage issues in this environment will also be briefly addressed.

* Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.