|
|
| Abstracts
| Invited
Plenary Talk |
| Pietro
Musumeci: Very High Energy Gain in the Neptune
IFEL experiment |
We report on the
observation of energy gain in excess of 20 MeV at
the Inverse Free Electron Laser Accelerator experiment
at the Neptune Laboratory at UCLA. A 14.5 MeV electron
beam is injected in a 50 cm long undulator strongly
tapered in period and field amplitude. The IFEL
driver is a CO2 10.6 micron laser with power larger
than 300 GW. The Rayleigh range of the laser, ~1.8
cm, is much shorter than the undulator length so
that the interaction is diffraction dominated. A
few per cent of the injected particles are trapped
in a stable accelerating bucket. Electrons with
energies up to 35 MeV are measured in a magnetic
spectrometer. Experimental results on the dependence
of the acceleration on injection energy, laser focus
position, and laser power are discussed. Three-dimensional
simulations, in good agreement with the measured
electron energy spectrum, indicate that most of
the acceleration occurs in the first 25-30 cm of
the undulator, corresponding to an energy gradient
larger 70 MeV/m. The measured energy spectrum also
indicates that higher harmonic IFEL interaction
is taking place in the second section of the undulator.
|
| Gerald
Dugan: Advanced
Accelerator System Requirements Overview |
| This paper
will review the requirements on advanced accelerator
systems as applied to next-generation linear colliders.
The design issues and requirements for TeV-scale
linear colliders will be discussed, and the challenges
involved in developing affordable extensions to
higher energies, utilizing advanced accelerator
concepts, will be presented. |
| Rami
Kishek: Modeling of Halos and Intense Beams
* |
| How
intense a charged particle beam can we transport?
The answer depends on our ability to limit deterioration
of beam quality from halo formation and other mechanisms
of emittance growth. Beam halos in particular introduce
other undesirable side effects such as activation
of the accelerator structures and increasing background
in detectors. So how do halos originate and under
what circumstances? A review of halo studies in
intense beams is presented with working examples
from simulation studies modeling the University
of Maryland Electron Ring (UMER).
* This work is funded by US Dept. of Energy grant
numbers DE-FG02-94ER40855 and DE-FG02-92ER54178.
|
| John
Lewellen: High-Brightness
Injector Modeling |
| There are many aspects
to the successful conception, design, fabrication
and operation of high-brightness electron beam sources.
Accurate and efficient modeling of the injector
are critical to all phases of the process, from
evaluating initial ideas to successful diagnosis
of problems during routine operation. The basic
modeling tasks will vary from design to design,
according to the basic nature of the injector (dc,
rf, hybrid, etc.), the type of cathode used (thermionic,
photo, field emission, etc.) and "macro"
factors such as average beam current and duty factor,
as well as the usual list of desired beam properties.
The injector designer must be at least aware of,
if not proficient at addressing, the multitude of
issues which arise from these considerations; and,
as high-brightness injectors continue to move out
of the laboratory and into the user facility or
instrument, the number of such issues will continue
to expand.
This talk will begin with a general discussion
of injector modeling philosophy, and a review
of some of the "standard" codes used
for rf-based designs. Next, some of the issues
related to transitioning a high-brightness injector
from laboratory instrument to subcomponent status
will be considered within the context of performance
modeling. The talk concludes with a discussion
of potential future paths, emphasizing multiphysics
modeling and more-integrated design.
|
| Simon
Hooker: Review of laser guiding experiments |
| A common
requirement for all laser-driven plasma accelerators
is the propagation of one or more intense beams
of radiation through a plasma. The distance over
which the driving laser maintains an intensity close
to the focal intensity is a significant factor determining
the acceleration that is achieved. In the absence
of any method to guide the laser radiation, the
laser-plasma interaction length is limited by diffraction
to the order of the Rayleigh range, which for the
laser parameters of interest is typically only a
few millimetres. In this talk we describe and explain
the operation of waveguides able to channel laser
pulses with intensities greater than 10^16 W/cm^2
over lengths significantly longer than the Rayleigh
range. These include: grazing-incidence guiding,
relativistic channelling, and several types of plasma
waveguide. For each technique the recent experimental
work will be reviewed and their prospects for application
to laser-driven accelerators assessed. |
| Igor
Pogorelsky: Gas lasers for strong field
applications |
| We review a diverse
field of the gas laser technology. Gas lasers cover
a spectral range from UV to Far-IR and are capable
to produce diffraction limited beams of the kilowatt
and even megawatt average power and wall plug efficiency
up to 70%. Atomic, molecular and excimer lasers
employ a variety of pumping schemes including electric
discharge, electron beams, optical and chemical
pumping. Among these lasers, we identify available
options and possible candidates for producing relativistically
strong (a>1) pico- and femtosecond pulses. We
review several ongoing projects in this field. Special
attention is given to picosecond CO2 lasers that
proved to be a valuable tool for strong-field physics
applications. Several advanced accelerator schemes
benefit from a long wavelength (lambda=10 um) of
the CO2 lasers. This facilitates structure-based
accelerators, production of micro-bunches and their
re-phasing to the laser field. The last feature
is important for demonstrating monoenergetic and
multi-staged electron acceleration. Ponderomotive
energy of the electron in the laser field is proportional
to the lambda squared that can be utilized in the
plasma based schemes, ion acceleration, Thomson
scattering, and other processes. Finally, we will
analyze possibilities for generating CO2 laser pulses
of the petawatt peak power and a-few-cycles duration. |
| Marc
Ross: Diagnostics for High Energy Accelerators |
| High energy accelerators
face two frontiers, both related to the need to
increase luminosity in order to have a constant
event rate. First is the requirement for extreme
precision, beyond that which would have been labelled
ridiculous a generation ago. Second is the requirement
to operate with very high power beams. Typical values
for these parameters at the proposed linear collider
are 1 micron beam size and 10 MW beam power. A beam
profile monitor with 1% resolution must therefore
be able to distinguish a 1.01 um beam from a 1.00
micron beam, a difference of only a few atomic diameters.
These Diagnostics are used to ensure operation at
the highest possible collider luminosity. This is
done with a combination of clever ideas, brute force
conservative engineering and insightful operational
considerations. In addition to the above, the wealth
of information from the monitors must be redirected
back to the beam as directly as possible using automatic
feedback schemes. Instrumentation and feedback projects
are ideal for small groups with students because
of their intrinsic small size and fascinating basic
physics and hardware. Both the ATF at BNL and the
ATF at KEK have been key in the development of new
instrumentation. |
| Mitsuru
Uesaka: Femtosecond
Beam Sources and Applications |
| Short particle beam
science has been promoted by electron linac and
radiation chemistry up to picoseconds. Recently,
table-top TW laser enables several kinds of short
particle beams and pump-and-probe analyses. 4th
generation SR sources aim to generation and application
of about 100 fs X-ray. Thus, femtosecond beam science
has become one of the important field in advanced
accelerator concepts. By using electron linac with
photoinjector, about 200 fs single bunch and 3 fs
multibunchs are available. Tens femtoseconds monoenergetic
electron bunch is expected by laser plasma cathode.
Concerning the electron bunch diagnosis, we have
seen remarkable progress in streak camera, coherent
radiation spectroscopy, fluctuation method and E/O
crystal method. Picosecond time-resolved pump-and-probe
analysis by synchronizing electron linac and laser
is now possible, but the timing jitter and drift
due to several fluctuations in electronic devices
and environment are still in picoseconds. On the
other hand, the synchronization between laser and
secondary beam is done passively by an optical beam-splitter
in the system based on one TW laser. Therefore,
the timing jitter and drift do not intrinsically
exist there. The author believes that the femtosecond
time-resolved pump-and-probe analysis must be initiated
by the laser plasma beam sources. As to the applications,
picosecond time-resolved system by electron photoinjector/linac
and femtosecond laser are operating in more than
5 facilities for radiation chemistry in the world.
Ti:Sapphire-laser-based repetitive pump-and-probe
analysis started by time-resolved X-ray diffraction
to visualize the atomic motion. Nd:Glass-laser-based
single-shot analysis was performed to visualize
the laser ablation via the single-shot ion imaging.
The author expects that protein dynamics and ultrafast
nuclear physics would be the next interesting targets.
Monograph titled gFemtosecond Beam Scienceh
is published by Imperial College Press in 2004. |
| Santiago
Bernal: The University of Maryland Electron
Ring: a model recirculator for intense-beam physics
research |
| The University of
Maryland Electron Ring (UMER), designed for transport
studies of space-charge dominated beams in a strong
focusing lattice, is nearing completion. Low energy,
high intensity electron beams provide an excellent
model system for experimental studies with relevance
to all areas that require high quality, intense
charged-particle beams. In addition, UMER constitutes
an important tool for benchmarking of computer codes.
When completed, the UMER lattice will consist of
36 alternating-focusing (FODO) periods over an 11.5-m
circumference. Current studies in UMER over about
2/3 of the ring include beam-envelope matching,
halo formation, unsymmetrical focusing, and longitudinal
dynamics (beam bunch erosion and wave propagation.)
Near future, multi-turn operation of the ring will
allow us to address important additional issues
such as resonance-traversal, energy spread and others.
The main diagnostics are phosphor screens and capacitive
beam position monitors placed at the center of each
20-degree bending section. In addition, pepper-pot
and slit-wire emittance meters are in operation.
The range of beam currents used correspond to space
charge tune depressions from 0.2 to 0.8, which is
unprecedented for a circular machine. |
| Yoneyoshi
Kitagawa: Review of Advanced Accelerator
Concepts R & D in Japan |
| Since Tajima and
Dawson have proposed the concept of the laser accelerator
in1979, Japan has been devoting much efforts to
not only realizing the advanced laser accelerator,
but also making the current accelerators compact
in scale. As for the electron acceleration, the
Kitagawa group, Osaka University, has achieved the
capillary-guided acceleration of electrons to 100
MeV via the laser wake field. The 1 cm long glass
capillary confined a plasma of 6x10^16 cm^-3 over
1 cm. They apply their PW laser to the particle
acceleration. The Uesaka group, University of Tokyo,
once generated hot electrons via the wave-breaking
field in the prepulse at the gas jet edge. They
call it the plasma cathode. Hence the main pulse
wakefield accelerated them to 40 MeV. The Koyama
group, National Institute of Advanced Industrial
Science and Technology, observed non-Maxwellian
electron peaks at 7 MeV via the Raman scattering.
For the ion acceleration, The Daido group, Japan
Atomic Energy Research Institute APR, studied the
proton acceleration in the underdense plasma. The
Ogata group, Hiroshima University and the Nemoto
group, Central Research Institute of Electric Power
Industry, worked with the neutral beam and ion generation
via thin films. The Ogata group is trying the photonic
crystal acceleration, too. The Nishida and Yugami
group, Utsunomiya University, found the 200 GHz
radiation under a magnetized plasma. As for the
advanced rf accelerator, the Urakawa group, KEK,
developed the new photo-rf electron gun: 20 bunch
in 10 ps pulse 5 pimm mrad at 12.5 Hz. The Japan
Synchrotron Radiation Research Institute SPring-8
and the Himeji Institute of Technology groups are
also active in the photo rf cathodes. As well, we
look around the Asian community activities. Korea,
Taiwan, China, India and Israel have been greatly
grown in recent years to reach the world-class cutting
edge in this field. |
| Warren
Mori: Advances in simulation capability:
A path towards full-scale modeling of 10 GeV–100
GeV plasma-based accelerator stages |
| Modeling plasma-based
accelerators is a great challenge. These challenges
arise because of the need to accurately describe
three processes: the evolution of a laser or particle
beam through long regions of plasma, the generation
of the plasma wakefields that are generated, the
acceleration and beam loading of an intense trailing
bunch of particles. While fluid codes can model
important pieces of the problem, to include all
of the above processes will require particle-based
methods. Using fully explicit particle-in-cell methods,
requires ~5000 (particle beam driver) to ~100,000
(laser driver) CPU hours on today’s fastest
computers to model each GeV gain in energy. Clearly,
it would be impractical to use this method to model
10 – 100 GeV stages. In this talk I will describe
recent advances in modeling plasma-based accelerators
using particle-in-cell (PIC) methods. I will emphasize
the recent development of a fully three-dimensional,
fully parallelized, quasi-static PIC code called
QuickPIC that can model both laser driven and plasma
driven schemes including beam loading. I will show
that when all of the quasi-static equations are
included this method can reproduce the full PIC
results and provide a factor of 100-500 in computational
savings. I will show preliminary results from QuickPIC
on the propagation of the 50 GeV SLC beam through
meters of plasma. I will also briefly discuss how
the plasma based methods are impacting conventional
accelerator issues and I will describe recent advances
in full PIC modeling, emphasizing the science results.through
meters of plasma. I will also describe recent advances
in full PIC modeling, emphasizing the science results. |
|
|
