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| Abstracts
| Computational
Accelerator Physics |
| Yasuo
Fukui: A Muon Cooling Ring with Lithium
Lenses |
| For the final muon
cooling ring for a muon collider, a Higgs Factory,
we designed a muon cooling ring with Lithium lens
inserts. A normalized transverse equilibrium emittance
around 0.3 mm*rad was obtained in a tracking simulation
with hard edged magnet elements. The cooling capability
of the muon ring with realistic magnet elements
is also discussed. |
| Courtlandt
Bohn: Collective Modes and Colored Noise
as Beam-Halo Amplifiers |
| We demonstrate how
collective modes and colored noise conspire to produce
beam halo with much larger amplitude than could
be generated by either phenomenon separately. Collective
modes are inherent to nonequilibrium beams. Colored
noise arises from unavoidable machine transitions
and/or errors and influences the internal space-charge
force. Using lowest-order radial eigenmodes calculated
self-consistently for a direct-current, cylindrically
symmetric, warm-fluid Kapchinskij-Vladimirskij equilibrium,
we compare and contrast halo dynamics involving
collective modes against that involving a pure root-mean-square
mismatch. The difference is dramatic; collective
modes are centrally important to the dynamics of
halo formation in real beams. |
| Michael
Zeitlin: Complex Dynamics in Accelerator/Plasma
Physics: Localized States, Zoo of Patterns, Control,
Part I. Kinetic models: BBGKY, Vlasov-Maxwell/Poisson
and all that |
i) An
efficient approach is proposed for analysis of complex
dynamics inaccelerator/plasma physics models based
onthe full hierarchy of kinetic equations (BBGKY-like).Our
calculations are based on variational and multiresolution
approachesin the basis of polynomial algebrasof
various localized bases.We construct the representation
for hierarchy of distributionfunctions and dynamical
variables via the exact multiscale decompositionin
high-localizednonlinear eigenmodes. The corresponding
cut-off of infinite hierarchy,reductions to finite
dimensional subsets and accuracy of calculations
arebased on the new multiscale metric structure
of the whole Fock-like spaceof alldistribution functions.
We demonstrate the existence ofenergy confinement/fusion
in the small regions of the phase space.ii) A fast
and efficient numerical-analytical approachis proposed
for modeling the complex nonlinear collective behaviourin
the various forms of the generalized Vlasov-Maxwell/Poisson
systems (e.g., propagation of the intense charged
particle beams).We compare our approach with previous
ones, e.g.nonlinear delta F simulation and PIC modeling
and demonstrateits advantages. As the particular
limiting cases of our construction we have standard
KV/Klimontovich distributions.The solutions are
represented via the multiscale decomposition innonlinear
high-localized eigenmodes, whichcorresponds to the
full multiresolution expansion in all underlying
hiddenscales. In contrast with different approaches
wedo not use perturbation technique or linearization
procedures.Numerical modeling shows the creation
of different internalstructures from localized modes,
which are related tostable/unstable type of behaviour
and the correspondingpatterns (waveletons) formation.
Reduced algebraical structure provides the pure
algebraical control of stability/unstability scenario.Varioustypes
of of patterns (chaotic and localized) are controlled
i
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| Michael
Zeitlin: Complex Dynamics in Accelerator/Plasma
Physics: Localized States, Zoo of Patterns, Control,
Part II. RMS Envelope Dynamics, Beam-Beam Interaction
Models etc |
| i) We consider
a few reductions from nonlinear Vlasov-like equations
torms/rate equations (nonlinear models for dynamics
of high-brightnessbeams) for second moments related
quantities (with or withoutadditional equations
or/and constraints for energy and emittance). Our
analysis is based on variational--wavelet approach
torational (in dynamical variables) approximations
with possible related constraint equations. It allows
to control contributions to spectrum fromeach scale
ofunderlying multiscales and represent solutions
via multiscale nonlinear eigenmodes expansions.
Our approach provides the best convergenceproperties
of the corresponding exact representations and does
not useperturbations or/and linearization procedures.
Reduced algebraicalstructure provides the pure algebraical
control of stability/unstabilityscenario and appearance
of different type of behaviour (chaotic vs.localized
patterns) in space of parameters.ii)We consider
modeling for strong-strong beam-beam interactions
beyondthe standard perturbative methods.In our approach,
based on projection methods and efficient functionalspace
decomposition in localized bases with control of
convergence for anonlinear and/or singular integral
operators (Hilbert transform) based models, the
full possible spectrum, partly discovered before(discrete
coherent and possible incoherent oscillations),appears
as the result ofthe exact multiresolution/multiscale
fast convergent decomposition in the bases of high-localized
exact nonlinear modes.The constructed solutions
representthe full multiscale spectrum with contributions
from all internal hiddenmodesfrom the slow to fast
oscillating eigenmodes.The underlyingmethods provide
some sort of the algebraical control of the spectrum
andthe type of dynamical behaviour. |
| Bradley
Shadwick: Thermal Effects in Intense
Laser-Plasma Interactions |
| Intense laser-plasma
interaction experiments access a unique physical
regime wherein the plasma electrons experience highly
relativistic motion while the temperature (or more
correctly, momentum spread) is quite small and the
plasma is effectively collisionless. To study this
regime, we have recently developed a "warm"
fluid model where the width of the distribution
function is treated asymptotically. Unlike the collisional
case, in this regime the plasma is not in local
thermodynamic equilibrium and the pressure tensor
can be strongly anisotropic. Using this model, we
examine various experimentally relevantconfigurations,
comparing the results of our new model with results
of the traditional cold fluid approximation. A case
of particular interest which we study in detail
is that of a short-pulse pulse propagating in a
laser wakefield accelerator, where the initial plasma
temperature is on the order of 20eV. Within the
quasi-static approximation, the warm-fluid equations
for the momentum spread can be solved analytically.
We find there is no significant heating of the plasma
and that the anisotropy of both the pressure tensor
and the distribution function is large. We compare
these analytical results to numerical results fromboth
warm and cold fluid models. |
| Xiangyun
Chang: Compensation for bunch emittance
in a magnetization and space-charge dominated beam |
In order to obtain
sufficient cooling rates for the Relativistic Heavy
Ion Collider (RHIC) electron cooling, a bunched
beam with high bunch charge, high repetition frequency
and high energy is required and it is necessary
to use a “magnetized” beam, i.e., an
electron beam with non-negligible angular momentum.
Applying a longitudinal solenoid field on the cathode
can generate such a beam, which rotates around its
longitudinal axis in a field-free region. This paper
suggests how a magnetized beam can be accelerated
and transported from a RF photocathode electron
gun to the cooling section without significantly
increasing its emittance. The evolution of longitudinal
slices of the beam under a combination of space
charge, magnetization and energy spread is investigated,
using paraxial envelope equations and numerical
simulations. We find that we must modify the traditional
method of compensating for emittance as used for
normal non-magnetized beam with space charge to
account for magnetization. The results of computer
simulations of successful compensation are presented.Alternately,
we show an electron bunch density distribution for
which all slices propagate uniformly and which does
not require emittance compensation
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| Xiangyun
Chang: Design considerations for low field
short photo-injected RF electron gun with high charge
electron bunch followed by linac |
| The RF field and
space charge effect in a low field RF gun is given.
The cell lengths are modified to have maximum accelerating
efficiency. The modification introduces an extra
RF field slice emittance. The phase space evolution
of the following emittance compensation system is
presented taking into account the chromatic effect.
The emittance compensation mechanics for RF field
and chromatic effect induced emittance is similar
to that of compensating the space charge induced
emittance. But the requirements are different to
have best compensation for them. The beam waist
is far in front of linac entrance to have best compensation
for the RF field and chromatic effect induced emittance.
For low field RF gun with high charge electron bunch
this compensation is more important. |
| Dimitre
Dimitrov: The IONPACK library of Ionization
Algorithms for PIC Codes |
| Impact
and tunneling ionization physics play key roles
in both beam-drivenand laser-driven plasma accelerator
concepts [1,2,3]. The portable Clibrary IONPACK
is being developed to encapsulate ionization algorithms,for
use by particle-in-cell (PIC) codes written in Fortran
or C/C++.For example, IONPACK is being used with
the parallel VORPAL [4] code.We will discuss the
ionization algorithms and their implementation,
aswell as how IONPACK is linked with VORPAL. We
will review previousvalidation of the algorithms
via code benchmarking and comparisonwith experiment,
and we will present recent VORPAL simulations ofrelevance
to plasma-based particle accelerators.
[1] D.L. Bruhwiler et al., Phys. Rev. ST-AB 4,
101302 (2001).[2] D.L. Bruhwiler et al., Phys.
Plasmas 10 (2003), p. 2022.[3] D.L. Bruhwiler
et al., PAC Proc. (2003), p. 734.[4] C. Nieter
and J.R. Cary, J. Comp. Phys. 196 (2004), p. 448.
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| Gwenael
Fubiani: Studies of space charge effects
in ultrashort electron bunches |
| Laser
driven accelerators are capable of producing multi
nC, multi MeV electron beams with transverse and
longitudinal sizes on the order of microns. We present
theoretical studies of the transport of such electron
bunches in vacuum. The effects of space charge forces
and energy spread on longitudinal and transverse
bunch properties are evaluated for various bunch
lengths, energies and amount of charge. We provide
a comprehensive summary and limitations of analytical
methods available for the simulation of the wide
variety of beam distributions generated by plasma-based
accelerators: (i) high charges (~1 nC), large energy
spreads (100 %) compact electron bunches produced
by the self-modulated laser-wakefield-accelerator,
e.g., where the laser pulse size is many times the
plasma wavelength. (ii) lower charges (~ 10 pC),
small energy spreads (~ 2-5 %) compact electron
bunches produced by the colliding pulse laser-wakefield-accelerator
regime where two counterpropagationg laser pulses
(the drive pulse is resonnant) are used to inject
electrons into the wakefield. The various methods
discussed are respectively: envelope equations,
semi-analytical approach using ellipsoidal shells,
poisson solver and a 3-D point-to-point interaction
code. |
| Min
Hur: Averaged-PIC simulation of laser-plasma
interaction: pulse amplification by Raman backscattering
and wake field generation by two counterpropagating
lasers. |
| An average
particle-in-cell code (aPIC), based on an eikonal
formalism hasbeen developed [1] to simulate laser-plasma
interactions.The dominant laser modes are described
by their wave envelopes, avoidingthe need to resolve
the laser frequency.Appropriately time-averaged
equations describe the particle motion. Thecode
is fully kinetic, and thus includes critical physics
such as particletrapping and Landau damping.The
code has been initially employed to study Raman
backscatteramplification [2,3] of ultra-intense
pulses, where the dominant forces onthe particles
are the ponderomotive force of the beat-wave and
theself-consistent plasma electric field. The code
agrees well, in theappropriate regimes, with the
results from three-wave equations andparticle-in-cell
(PIC) simulations (XOOPIC).The effects of plasma
temperature on RBS amplification are studied. Ramanbackscatter
amplification is proposed as a successor technology
to chirpedpulse amplification. If realized, it should
have important applications inhigh-energy density
science. The low-noise implementation of a movingwindow
with an incoming radiation pulse and finite plasma
temperaturerequires some numerical subtleties which
will be discussed.1. M.S. Hur, et al, submitted
for publication2. V.M. Malkin, G. Shvets, and N.J.
Fisch, Phys. Plasmas 7, 2232 (2000).3. G. Shvets,
N.J. Fisch, A. Pukhov, and J. Meyer-ter-Vehn, Phys.
Rev. E60, 2218 (1999). |
| Amit
Kesar: Time and frequency domain models
for Smith-Purcell Radiation from a two dimensional
charge moving above a short grating |
| The
Smith-Purcell radiation (SPR) formed by an electron
bunch traveling above a grating is important for
determining bunch characteristics as well as a coherent
source in the THz regime. The SPR from a two dimensional
bunch moving above a finite length grating is studied
theoretically by two independent models: a finite-difference
time-domain (FDTD) simulation and an electric-field
integral equation (EFIE) method. A total-field/scattered-field
approach was used in the FDTD model to simulate
the bunch free-space fields incident on the grating.
A numerical example is presented by an ~18 MeV,
50 pC/mm, 200 micron bunch traveling 0.6 mm above
a 2.1 mm period echelle grating. Good agreement
is obtained between the two models. It is shown
that the EFIE method provides the same results as
the van den Berg model for an infinitely long, periodic
grating. Applications and limitations of these models
are discussed. |
| Chiping
Chen: Center-of-Mass Dynamics and Space-Charge
Limit of a Finite-Size Bunched Beam |
| We derive
the space-charge limit for a train of periodic finite-size
charged bunches which are slightly displaced from
the axis of a circular, perfectly conducting pipe.
The general calculation assumes that the bunches,
while periodic, may have arbitrary radial and longitudinal
density distributions with respect to the beam axis.
We present results for a few specific distributions,
as well as the limits of unbunched and single bunch
beams. Finally, we show how the bunched beam space-charge
limit along with the radial rms envelope equation
for a bunched beam is applied to predict operational
limits of periodic permanent magnet (PPM) focusing
klystrons that are being developed for the Next
Linear Collider. |
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