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| Abstracts
|
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.
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