
Abstracts
eBeam
Driven Accelerators 
David
Bruhwiler: Simulation of Ionization Effects
for HighDensity Positron Drivers in future Plasma
Wakefield Experiments 
The PWFA concept
has been proposed [1] as a potential energy doubler
for present or future electronpositron colliders.
Recent particleincell simulations have shown [2]
that the selffields of the required electron beam
driver can tunnel ionize neutral Li, leading to
plasma wake dynamics differing significantly from
that of a preionized plasma. It has also been shown,
for the case of a preionized plasma, that the plasma
wake of a positron driver differs strongly [3] from
that of an electron driver. We will present particleincell
simulations, using the OOPIC [4,5] code, showing
the effects of tunneling ionization on the plasma
wake generated by highdensity electron and positron
drivers. The results will be compared to previous
work on electron drivers with tunneling ionization
and positron drivers without ionization.Parameters
relevant to the E164 and E164x experiments at
SLAC will be considered.
[1] S. Lee et al., Phys. Rev. S.T. A&B 5,
011001 (2002).[2] D.L. Bruhwiler et al., Phys.
Plasmas 10 (2003), p. 2022.[3] S. Lee et al.,
Phys. Rev. E 64, 045501(R) (2001).[4] D.L. Bruhwiler
et al., Phys. Rev. STAB 4, 101302 (2001).[5]
D.L. Bruhwiler et al., PAC Proc. (2003), p. 734.

Eric
Colby: Potential Beams at ORION 
The discussion will
focus on possible operating modes (one bunch, two
bunch, short train, optically bunched train, etc.)
and beam properties at the ORION facility. Detailed
simulations of lowcharge lowenergy spread operation,
and preliminary simulations of high charge operation
will be briefly outlined, followed by an open discussion
of what future experiments will need, and what might
be possible to achieve. 
Mark
Hogan: Energy Gain in E164X 
In the plasma wakefield
accelerator, a short relativisticelectron bunch
drives a large amplitude plasma wave or wake. In
experiment E164X, we use the 28.5 GeV, ultrashort
(?80 femtosecond), high peakcurrent (?30 kiloamperes)
bunch now available at the Stanford Linear Accelerator
Center Final Focus Test Beam facility. The head
of this bunch fieldionizes a lithium vapor and
excites the wake, and the tail samples the accelerating
field. The latter is accomplished by setting the
plasma density to match the plasma wavelength to
the bunch length. After the plasma, the bunch is
dispersed in energy by an imaging magneticspectrometer.
Preliminary analysis shows that gradients in excess
of 15 GeV/m are excited over a plasma length of
approximately 10 cm, leading to energy gain on the
order of of 1.5 GeV, or about an order of magnitude
larger than energy gains reported to date. This
gradient is also three orders of magnitude larger
than that in the threekilometer long Stanford linear
accelerator that produces the incoming beam. These
results are obtained in a new regime for beamdriven
plasma accelerators in which the electron bunch
creates its own plasma. The current status of the
experiment as well as future plans will be discussed. 
Chengkun
Huang: Modeling Plasma Afterburner 
Plasma afterburner
has been proposed as one of the advanced acceleration
schemes for the future linear collider. In this
design, a high energy electron(or positron) drive
beam from the SLAC linac will propagate in a plasma
section of density about one order of magnitude
lower than the peak beam density. The particle beam
drives a plasma wave and generates a strong wakefield
which has a phase velocity equal to the velocity
of the beam and can be used to accelerate part of
the drive beam or a trailing beam. Several issues
such as the efficient transfer of energy and the
stable propagation of the particle beam in the plasma
are critical to the afterburner experiment. We investigated
the nonlinear beamplasma interaction in such scenario
using 3D computer modeling code QuickPIC. Simulation
results for electron acceleration, beamloading
and hosing instability will be presented. 
Wei
Lu: Linear and nonlinear plasma wakes driven
by electron beam 
A theoretic model
for the electron blowout regime has beem constructed
to understand the plasma wakes driven by electron
beams. Both the linearlike scaling in the nonrelativistic
blowout regime and the saturation behavior in the
ultrarelativistic blowout regime can be understood
by this model. we will present these results in
this talk. 
James
Rosenzweig: ENERGY LOSS OF A HIGH CHARGE
BUNCHED ELECTRON BEAM IN PLASMA: SIMULATIONS, SCALING,
AND ACCELERATING WAKEFIELDS 
The energy loss and
gain of a beam in the nonlinear, “blowout”
regime of the plasma wakefield accelerator (PWFA),
which features ultrahigh accelerating fields, linear
transverse focusing forces, and nonlinear plasma
motion, has been asserted, through previous observations
in simulations, to scale linearly with beam charge.
Additionally, from a recent analysis by Barov, et
al., it has been concluded that for an infinitesimally
short beam, the energy loss is indeed predicted
to scale linearly with beam charge for arbitrarily
large beam charge. This scaling is predicted to
hold despite the onset of a relativistic, nonlinear
response by the plasma, when the number of beam
particles occupying a cubic plasma skindepth exceeds
that of plasma electrons within the same volume.
This paper is intended to explore the deviations
from linear energy loss using 2D particleincell
simulations that arise in the case of experimentally
relevant finite length beams. The peak accelerating
field in the plasma wave excited behind the finitelength
beam is also examined, with the artifact of wave
spiking adding to the apparent persistence of linear
scaling of the peak field amplitude into the nonlinear
regime. At large enough normalized charge, the linear
scaling of both decelerating and accelerating fields
collapses, with serious consequences for plasma
wave excitation efficiency. Using the results of
parametic PIC studies, the implications of these
results for observing severe deviations from linear
scaling in present/planned experiments are discussed. 
Caolionn
OConnell: Field Ionization of a Neutral
Lithium Vapor using a 28.5 GeV Electron Beam 
The E164 and E164X plasma
wakefield experiments study beamplasma interactions
at the Stanford Linear Acceleration Center (SLAC).
A new regime of physics is being explored due to
SLAC’s recent ability (Summer 2002) to compress
the incoming electron bunch length to 100 microns
and smaller. In particular, the higher beam density
allows the electric field of an incoming beam to
ionize a neutral vapor. The field ionization effects
are characterized by the beam’s energy loss
through a 3040cm Lithium vapor column. The preliminary
results from the field ionization analysis will
be presented. 

