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Siemann, R.

Paper Title Page
WEXKI02 Demonstration of Optical Microbunching and Net Acceleration at 0.8 microns 1894
 
  • C. M.S. Sears, E. R. Colby, R. Ischebeck, C. Mcguinness, R. Siemann, J. E. Spencer, D. R. Walz
    SLAC, Menlo Park, California
  • R. L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
 
  Formation, diagnosis, and acceleration of electron microbunches from an rf linac generated beam is presented. A PM-EM hybrid IFEL/chicane buncher was designed and commissioned to produce optical bunch trains suitable for injection into solid-state laser accelerators. Microbunching is independently diagnosed via coherent optical tranisition radiation (COTR). Net acceleration is obtained by splitting the laser power between the IFEL and an inverse transition radiation (ITR) accelerator.  
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THPMS015 Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures 3026
 
  • M. C. Thompson, M. C. Thompson
    LLNL, Livermore, California
  • H. Badakov, J. B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • M. J. Hogan, R. Ischebeck, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • P. Muggli
    USC, Los Angeles, California
  • A. Scott
    UCSB, Santa Barbara, California
  • R. B. Yoder
    Manhattan College, Riverdale, New York
 
  Funding: This work was performed under the auspices of the US Department of Energy under Contracts No. DE-FG03-92ER40693, DE-AC02-76SF00515, W-7405-ENG-48, and DE-FG02-92-ER40745.

The breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been measured. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 microns. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compression of the electron bunch. The onset of breakdown, as indicated by a bright discharge, was found to correlate to a surface field of about 4 GV/m. An analysis of the damage sustained to the beam-exposed fibers, and its correlation to field amplitude, is also reported.

 
THPMS047 Emittance Growth from Multiple Coulomb Scattering in a Plasma Wakefield Accelerator 3097
 
  • N. A. Kirby, M. K. Berry, I. Blumenfeld, M. J. Hogan, R. Ischebeck, R. Siemann
    SLAC, Menlo Park, California
 
  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.

 
THPMS050 Designing Photonic Bandgap Fibers for Particle Acceleration 3103
 
  • R. J. Noble, E. R. Colby, B. M. Cowan, C. M.S. Sears, R. Siemann, J. E. Spencer
    SLAC, Menlo Park, California
 
  Funding: Supported by U. S. Dept. of Energy contract DE-AC02-76SF00515

Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a periodic PBG fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the central defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity near the speed of light (SOL). We explore the design of the defect geometry to support well-confined accelerating modes in such PBG fibers. The details of the surface boundary separating the defect from the surrounding matrix are found to be the critical ingredients for optimizing the accelerating mode properties. We give examples of improved accelerating modes in fiber geometries with modified defect surfaces.

 
THPMS052 Optical Wakefield from a Photonic Bandgap Fiber Accelerator 3106
 
  • C. M.S. Sears, E. R. Colby, B. M. Cowan, R. Ischebeck, C. Mcguinness, R. J. Noble, R. Siemann, J. E. Spencer, D. R. Walz
    SLAC, Menlo Park, California
  • R. L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
 
  Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for there high coupling impedance and high damage threshold (>2 GV/m). As a first step in preparing a PBG accelerator, we propose to first observe the optical wakefield induced incoherently by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are coupled into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light phase velocities. By observing the wakefield using a spectrometer, the accelerating mode frequencies are determined.  
WEYKI01 Results of the Energy Doubler Experiment at SLAC 1910
 
  • M. J. Hogan, I. Blumenfeld, F.-J. Decker, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  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.

The costs and the time scales of colliders intended to reach the energy frontier are such that it is important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators a drive beam, either laser or particle, produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultra-high accelerating fields over a substantial length to achieve a significant energy gain. More than 42 GeV energy gain was achieved in an 85 cm long plasma wakefield accelerator driven by a 42 GeV electron drive beam at the Stanford Linear Accelerator Center (SLAC). Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of ~52 GV/m. This effectively doubles their energy, producing the energy gain of the 3 km long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch.

 
slides icon Slides  
THPMS027 Dielectric Wakefield Accelerator Experiments at the SABER Facility 3058
 
  • G. Travish, H. Badakov, A. M. Cook, J. B. Rosenzweig, R. Tikhoplav
    UCLA, Los Angeles, California
  • M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • P. Muggli
    USC, Los Angeles, California
  • M. C. Thompson
    LLNL, Livermore, California
 
  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.

 
THPMS029 Beam Head Erosion in Self-ionized Plasma Wakefield Accelerators 3064
 
  • M. Zhou, C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori
    UCLA, Los Angeles, California
  • M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  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)

 
THPMS033 Scaling of Energy Gain with Plasma Parameters in a Plasma Wakefield Accelerator 3076
 
  • P. Muggli, T. C. Katsouleas, E. Oz
    USC, Los Angeles, California
  • I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
 
  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.

Systematic measurements of energy gain as a function of plasma parameters in the SLAC electron beam-driven plasma wakefield acceleration (PWFA) experiments lead to very important understanding of the beam-plasma interaction. In particular, measurements as a function of the plasma length Lp show that the energy gain increases linearly with Lp in the 10 to 30 cm range. Based on this scaling, the plasma was subsequently lengthened to Lp=90cm, resulting in the first demonstration of the doubling of the energy of a fraction of the incoming 42GeV electrons*. The peak accelerating gradient is larger than 40GV/m and is sustained over meter-scale plasma lengths. These measurements also reveal that the optimum plasma density for acceleration is about 2.7·1017/cc, larger than the value predicted by the linear theory for the approximately 20 microns bunch length, confirming that the experiment is conducted in the non-linear regime of the PWFA. Detailed experimental results will be presented.

* "Energy doubling of 42 GeV electrons in a meter scale plasma wakefield accelerator", I. Blumenfeld et. al., Nature, 2006, accepted

 
THPMS040 Correlation of Beam Parameters to Decelerating Gradient in the E-167 Plasma Wakefield Acceleration Experiment 3091
 
  • I. Blumenfeld, M. K. Berry, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  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.

 
THPMS055 Beam Dynamics Measurements for the SLAC Laser Acceleration Experiment 3115
 
  • J. E. Spencer, E. R. Colby, R. Ischebeck, D. J. McCormick, C. Mcguinness, J. Nelson, R. J. Noble, C. M.S. Sears, R. Siemann
    SLAC, Menlo Park, California
  • T. Plettner
    Stanford University, Stanford, Califormia
 
  Funding: Work supported by U. S. Dept. of Energy contract DE-AC02-76SF00515.

The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun has been installed with diagnostics and a low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV. This is followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range (2\%), high resolving power (104) spectrometer (HES) for electron bunch analysis. Emittance compensating solenoids and the LES are used to tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5° extraction line provide 1:1 phase space transfer without use of sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes of a few microns at the IP (or HES object) allow tests of microscale structures as well as high resolving power at the image of the HES. Tolerances, tuning sensitivities and diagnostics are discussed together with the latest commissioning results and their comparison to design expectations.

 
THPMS080 Inverse-Transition Radiation Laser Acceleration Experiments at SLAC 3172
 
  • T. Plettner, R. L. Byer
    Stanford University, Stanford, Califormia
  • E. R. Colby, R. Ischebeck, C. Mcguinness, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
    SLAC, Menlo Park, California
 
  We present a series of laser-driven particle acceleration experiments that are aimed at studying laser-particle acceleration as an inverse-radiation process. To this end we employ a semi-open vacuum setup with a thin planar boundary that interacts with the laser and the electromagnetic field of the electron beam. Particle acceleration from different types of boundaries will be studied and compared to the theoretical expectations from the Inverse-radiation picture and the field path integral method. We plan to measure the particle acceleration effect from transparent, reflective, black, and rough surface boundaries. While the agreement between the two acceleration pictures is straightforward to prove analytically for the transparent and reflective boundaries the equivalence is not clear-cut for the absorbing and rough-surface boundaries. Therefore, experimental observation may be the most reliable method for establishing the appropriate model for the interaction of the laser field with the particle beam in the presence of a loaded vacuum structure.  
FRPMS072 Timing Stability and Control at the E163 Laser Acceleration Experiment 4195
 
  • C. Mcguinness, E. R. Colby, R. Ischebeck, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
    SLAC, Menlo Park, California
  • R. L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
 
  Funding: DOE: DE-AC02-76SF00515 and DE-FG06-97ER41276

The laser acceleration experiments conducted for the E163 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot-by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.

 
FRPMS067 Energy Measurement in a Plasma Wakefield Accelerator 4168
 
  • R. Ischebeck, M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  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.

 
FRPMS070 Emittance Measurement of Trapped Electrons from a Plasma Wakefield Accelerator 4183
 
  • N. A. Kirby, M. K. Berry, I. Blumenfeld, F.-J. Decker, M. J. Hogan, R. Ischebeck, R. H. Iverson, R. Siemann, D. R. Walz
    SLAC, Menlo Park, California
  • C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • T. C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
 
  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.