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AAC'04 Agenda
AAC'04 Poster
Organizing Committee
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e-Beam Driven Accelerators
David Bruhwiler: Simulation of Ionization Effects for High-Density Positron Drivers in future Plasma Wakefield Experiments
  The PWFA concept has been proposed [1] as a potential energy doubler for present or future electron-positron colliders. Recent particle-in-cell simulations have shown [2] that the self-fields 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 particle-in-cell simulations, using the OOPIC [4,5] code, showing the effects of tunneling ionization on the plasma wake generated by high-density 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 E-164 and E-164x 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. ST-AB 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 low-charge low-energy 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 E-164X
  In the plasma wakefield accelerator, a short relativistic-electron bunch drives a large amplitude plasma wave or wake. In experiment E-164X, we use the 28.5 GeV, ultra-short (?80 femtosecond), high peak-current (?30 kiloamperes) bunch now available at the Stanford Linear Accelerator Center Final Focus Test Beam facility. The head of this bunch field-ionizes 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 magnetic-spectrometer. 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 three-kilometer long Stanford linear accelerator that produces the incoming beam. These results are obtained in a new regime for beam-driven 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 beam-plasma interaction in such scenario using 3D computer modeling code QuickPIC. Simulation results for electron acceleration, beam-loading 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 linear-like scaling in the non-relativistic blowout regime and the saturation behavior in the ultra-relativistic blowout regime can be understood by this model. we will present these results in this talk.
  The energy loss and gain of a beam in the nonlinear, “blowout” regime of the plasma wakefield accelerator (PWFA), which features ultra-high 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 skin-depth exceeds that of plasma electrons within the same volume. This paper is intended to explore the deviations from linear energy loss using 2D particle-in-cell simulations that arise in the case of experimentally relevant finite length beams. The peak accelerating field in the plasma wave excited behind the finite-length 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 beam-plasma 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 30-40cm Lithium vapor column. The preliminary results from the field ionization analysis will be presented.