| Paper | Title | Page |
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| THPMS027 | Dielectric Wakefield Accelerator Experiments at the SABER Facility | 3058 |
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Funding: Work supported in part by Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92-ER40745, DE-FG03-92ER40693 and W-7405-ENG-48 Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC FFTB, are foreseen to be produced soon at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of >10 GV/m. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 μm and 200 μm ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in excess of 4 GV/m (2 GV/m accelerating field) in fused silica. With the construction and commissioning of the SABER facility at SLAC, new experiments are made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. The E169 collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures. |
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| THPMS029 | Beam Head Erosion in Self-ionized Plasma Wakefield Accelerators | 3064 |
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Funding: Work supported by Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345
In the recent plasma wakefield accelerator experiments at SLAC, the energy of the particles in the tail of the 42 GeV electron beam were doubled in less than one meter [1]. Simulations suggest that the acceleration length was limited by a new phenomenon – beam head erosion in self-ionized plasmas. In vacuum, a particle beam expands transversely in a distance given by beta*. In the blowout regime of a plasma wakefield [2], the majority of the beam is focused by the ion channel, while the beam head slowly spreads since it takes a finite time for the ion channel to form. It is observed that in self-ionized plasmas, the head spreading is exacerbated compared to that in pre-ionized plasmas, causing the ionization front to move backward (erode). A simple theoretical model is used to estimate the upper limit of the erosion rate for a bi-gaussian beam by assuming free expansion of the beam head before the ionization front. Comparison with simulations suggests that half this maximum value can serve as an estimate for the erosion rate. Critical parameters to the erosion rate are discussed.
[1] I. Blumenfeld et al., Nature 445, 741(2007)[2] J. B. Rosenzweig et al., Phys. Rev. A 44, R6189 (1991) |
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| THPMS040 | Correlation of Beam Parameters to Decelerating Gradient in the E-167 Plasma Wakefield Acceleration Experiment | 3091 |
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Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345 Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch length and beam waist location were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the decelerating gradient. Limits on the transformer ratio will also be discussed. The results are compared to simulation. |
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| THPMS047 | Emittance Growth from Multiple Coulomb Scattering in a Plasma Wakefield Accelerator | 3097 |
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Funding: This work was supported by the Department of Energy contracts DE- AC02-76SF00515 Emittance growth is an important issue for plasma wakefield accelerators (PWFAs). Multiple Coulomb scattering (MCS) is one factor that contributes to this growth. Here, the MCS emittance growth of an electron beam traveling through a PWFA in the blow out regime is calculated. The calculation uses well established formulas for angular scatter in a neutral vapor and then extends the range of Coulomb interaction to include the effects of traveling through an ion column. Emittance growth is negligible for low Z materials; however, becomes important for high Z materials. |
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| FRPMS067 | Energy Measurement in a Plasma Wakefield Accelerator | 4168 |
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Funding: DOE DE-AC02-76SF00515 (SLAC), DE-FG02-92-ER40745, DE-FG03-92ER40745, DE-FC02-01ER41179, DE-FG03-92ER40727, DE-FG02-03ER54721, DE-F52-03NA00065:A004, DE-AC-0376SF0098, NSF ECS-9632735, NSF-Phy-0321345 Particles are leaving the meter-long plasma wakefield accelerator with a large energy spread. To determine the spectrum of these particles, four diagnostics have been set up. These were used to determine energies of the particles that gain energy in the plasma, those that lose energy by driving the wake and the self-injected particles that are accelerated from rest. |
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| FRPMS070 | Emittance Measurement of Trapped Electrons from a Plasma Wakefield Accelerator | 4183 |
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Funding: This work was supported by the Department of Energy contracts DE- AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745. DE- FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345 Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC showed trapping of plasma electrons. These trapped electrons appeared on an energy spectrometer with smaller transverse size than the beam driving the wake. A connection is made between transverse size and emittance; due to the spectrometer?s resolution, this connection allows for placing an upper limit on the trapped electron emittance. The upper limit for the lowest normalized emittance measured in the experiment is 1 mm·mrad. |