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| TPAE040 | Nonlinear Theory in the Blowout Regime for Both Particle Beam and Laser Drivers | |
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Funding: DOE and NSF. Recent progress in both PWFA and LWFA has confirmed the promising characteristics of the blowout regime. So it is worthwhile to understand the wake excitation process and other relevant issues (e.g. self trapping mechanism, laser self guiding, scaling laws) in this regime. Because the plasma electrons always cross each other in the blowout regime, it is not possible to use a fluid model. Instead, we use a particle picture. Based on the analysis of the innermost particle trajectory, we have developed a self-consistent theory for this regime. For particle beam drivers, we explained why linear theory can be a good approximation in the weakly nonlinear blowout regime and also obtained formulas to predict the wake amplitude. In the strongly nonlinear blowout regime (relativistic or ultra-relativistic), the theory can predict the wake structures and amplitudes in terms of the particle beam or laser pulse intensity. The theory also provides a basis for a beam loading theory in the blowout regime as well a basis for finding optimum driver profile. We will also give some results on the energy gain and total charge scalings based on this theory. |
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| TPAE046 | Modeling Self-Ionized Plasma Wakefield Acceleration for Afterburner Parameters Using QuickPIC | 2905 |
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Funding: DOE A plasma wakefield accelerator (PWFA) has been proposed as a way to double the energy of a future linear collider. This afterburner concept will require meter long uniform plasmas. For the parameters envisaged in possible afterburner stages, the self-fields of the particle beam are intense enough to tunnel ionize some neutral gases such as lithium. Tunnel ionization has been investigated as a way for the beam itself to create the plasma.* Furthermore, tunnel ionization in a neutral or partially pre-ionized gas may create new plasma electrons and alter the plasma wake.*,** Unfortunately, it is not possible to model a PWFA with afterburner parameters using the models described in Bruhwiler et al. and Deng et al. Here we describe the addition of a tunnel ionization package using the ADK model into QuickPIC, a highly efficient quasi-static particle in cell (PIC) code which can model a PWFA with afterburner parameters. There is excellent agreement between QuickPIC and OSIRIS(a full PIC code) for pre-ionized plasmas. Effects of self-ionization on hosing instability –one of the most critical issues to overcome to make an afterburner a reality – for a bunch propagating in a plasma hundreds of betatron oscillations long will be discussed. *D. L. Bruhwiler et al., Phys. Plasmas 10 (2003), p. 2022. **S. Deng et al., Phys. Rev. E, 68, 047401 (2003). |
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| TPAE025 | Field Ionization of Neutral Lithium Vapor using a 28.5 GeV Electron Beam | 1904 |
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| The E164/E164X plasma wakefield experiment studies beam-plasma interactions at the Stanford Linear Acceleration Center (SLAC). Due to SLAC recent ability to variably compress bunches longitudinally from 650 microns down to 20 microns, the incoming beam is sufficiently dense to field ionize the neutral Lithium vapor. The field ionization effects are characterized by the beam’s energy loss through the Lithium vapor column. Experimental results are presented. | ||
| TPAE041 | Modeling TeV Class Plasma Afterburners | 2666 |
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Funding: Work supported by DOE and NSF. Plasma wakefield acceleration can sustain acceleration gradients three orders of magnitude larger than conventional RF accelerator. In the recent E164X experiment, substantial energy gain of about 3Gev has been observed. Thus, a plasma afterburner, which has been proposed to double the incoming beam energy for a future linear collider, is now of great interest. In an afterburner, a particle beam drives a plasma wave and generates a strong wakefield which has a phase velocity equal to the velocity of the beam. This wakefield can then 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 both the drive and trailing beams in the plasma are critical to the afterburner concept. We investigate the nonlinear beam-plasma interaction in such scenario using the 3D computer modeling code QuickPIC. We will report the latest simulation results of both 50 GeV and 1 TeV plasma afterburner stages for electrons including the beam-loading of a trailing beam. Analytic analysis of hosing instability in this regime will be presented. |
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| TPAE042 | Beam Matching to a Plasma Wake Field Accelerator Using a Ramped Density Profile at the Plasma Boundary | 2702 |
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Funding: DOE Grant No. DE-FG03-92ER40727. An important aspect of plasma wake field accelerators (PWFA) is stable propagation of the drive beam. In the under dense regime, the drive beam creates an ion channel which acts on the beam as a strong thick focusing lens. The ion channel causes the beam to undergo multiple betatron oscillations along the length of the plasma. There are several advantages if the beam size can be matched to a constant radius. First, simulations have shown that instabilities such as hosing are reduced when the beam is matched. Second, synchrotron radiation losses are minimized when the beam is matched. Third, an initially matched beam will propagate with no significant change in beam size in spite of large energy loss or gain. Coupling to the plasma with a matched radius can be difficult in some cases. This paper shows how an appropriate density ramp at the plasma entrance can be useful for achieving a matched beam. Additionally, the density ramp is helpful in bringing a misaligned trailing beam onto the drive beam axis. A plasma source with boundary profiles useful for matching has been created for the PWFA experiments at SLAC. |
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| TPAE058 | Plasma Dark Current in Self-ionized Plasma Wake Field Accelerators (PWFA) | 3444 |
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| Particle trapping is investigated with experiment, theory and simulations for conditions relevant to beam driven Plasma Wake Field Accelerators. Such trapping produces plasma dark current when the wakefield aplitude is above a threshold values and may place a limit on the maximum acceleration gradient in a PWFA. Trapping and dark current are enhanced when in an ionizing plasma, that is self-ionized by the beam as well as in gradual density gradients. In the E164X conducted at the Stanford Linear Accelerator Center by a collaboration of USC, UCLA and SLAC, evidence of trapping has been observed. Here we present experimental results and a simplified analytical model of the particle trapping threshold which is compared to simulations done with an object oriented fully parallel 3-D PIC code OSIRIS. | ||
| RPAE019 | Positron Source from Betatron X-Rays Emitted in a Plasma Wiggler | 1625 |
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| In the E-167 plasma wakefield accelerator (PWFA) experiments in the Final Focus Test Beam (FFTB) at the Stanford Linear Accelerator Center (SLAC), an ultra-short, 28.5 GeV electron beam field ionizes a neutral column of Lithium vapor. In the underdense regime, all plasma electrons are expelled creating an ion column. The beam electrons undergo multiple betatron oscillations leading to a large flux of broadband synchrotron radiation. With a plasma density of 3x1017 cm-3, the effective focusing gradient is near 9 MT/m with critical photon energies exceeding 50 MeV for on-axis radiation. A positron source is the initial application being explored for these X-rays, as photo-production of positrons eliminates many of the thermal stress and shock wave issues associated with traditional Bremsstrahlung sources. Photo-production of positrons has been well-studied; however, the brightness of plasma X-ray sources provides certain advantages. In this paper, we present results of the simulated radiation spectra for the E-167 experiments, and compute the expected positron yield. |