Author: Joshi, C.
Paper Title Page
MOP016 Preliminary Simulations of Plasma Wakefield Accelerator Experiments at FACET 136
 
  • W. An, C. Joshi, W. Lu, W.B. Mori
    UCLA, Los Angeles, California, USA
  • M.J. Hogan
    SLAC, Menlo Park, California, USA
  • C. Huang
    LANL, Los Alamos, New Mexico, USA
 
  Funding: This work is supported by USDoE under DE-FC02-07ER41500, DE-FG02-92ER40727 and NSF under NSF PHY-0904039, PHY-0936266.
Recent experiments on former facility FFTB at SLAC has demonstrated that a single electron beam driven Plasma Wakefield Accelerator (PWFA) can be produced with an accelerating gradient of 52 GeV/m over a meter-long scale*. If another electron bunch is properly loaded into such a wakefield, it will obtain a high energy gain in a short distance as well as a small energy spread. Such PWFA experiment with two bunches will be performed in FACET, which is a new facility at SLAC**. Simulation results show that with possible beam parameters in FACET the first electron bunch (with less current than that in the FFTB experiment) can still produce a meter-long plasma column with a density of 5x1016 cm-3 via field ionization when we use a gas with a lower ionization energy. The second electron bunch can have a 10 GeV energy gain with a very narrow energy spread. If a pre-ionized plasma is used instead of the neutral gas, the energy gain of the second bunch can be enhanced to 30 GeV.
* I. Blumenfeld et al., Nature 445, 741 (2007).
** M. J.Hogan, et al.,NewJ. Phys.12, 055030(2010).
 
 
MOP088 A High Transformer Ratio Plasma Wakefield Accelerator Scheme for FACET 265
 
  • R.J. England, J.T. Frederico, M.J. Hogan
    SLAC, Menlo Park, California, USA
  • W. An, C. Joshi, W. Lu, W.B. Mori
    UCLA, Los Angeles, California, USA
  • P. Muggli
    USC, Los Angeles, California, USA
 
  Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515
The ideal drive beam current profile for the plasma wakefield accelerator (PWFA) has been predicted by 1D and 2D simulations to be characterized by a triangular ramp that rises linearly from head to tail, followed by a sharp drop. A technique for generating such bunches experimentally was recently demonstrated. We present here an adaptation of this scheme to generate ramped bunches using the 23 GeV electron beam produced in the first two-thirds of the SLAC linac, and discuss plans to implement this scheme for high transformer ratio demonstration experiments at the FACET plasma wakefield accelerator facility.
 
 
MOP101 Numerical Study of Self and Controlled Injection in 3-Dimensional Laser-Driven Wakefields 286
 
  • A.W. Davidson, R. Fenseca, C. Joshi, W. Lu, J.L. Martins, W.B. Mori, L.O. Silva
    UCLA, Los Angeles, California, USA
 
  Funding: DOE and NSF
In plasma based accelerators (LWFA and PWFA), the methods of injecting high quality electron bunches into the accelerating wakefield is of utmost importance for various applications. Understanding how injection occurs in both self and controlled scenarios is therefore important. To simplify this understanding, we start from single particle motion in an arbitrary traveling wave wakefields, an electromagnetic structure with a fixed phase velocity(e.g., wakefields driven by non-evolving drivers), and obtain the general conditions for trapping to occur. We then compare this condition with high fidelity 3D PIC simulations through advanced particle and field tracking diagnostics. Numerous numerical convergence tests were performed to ensure the correctness of the simulations. The agreement between theory and simulations helps to clarify the role played by driver evolution on injection, and a physical picture of injection first proposed in * is confirmed through simulations. Several ideas, including ionization assisted injection, for achieving high quality controlled injection were also explored and some simulation results relevant to current and future experiments will be presented.
*W. Lu et al., PRSTAB 10, 061301, 2007
 
 
MOP142 Development of Picosecond CO2 Laser Driver for an MeV Ion Source 355
 
  • S. Tochitsky, D.J. Haberberger, C. Joshi
    UCLA, Los Angeles, California, USA
 
  Funding: This work is supported by DOE grant DE-FG02-92ER40727.
Laser-Driven Ion Acceleration in thin foils has demonstrated high-charge, low-emittance MeV ion beams with a picosecond duration. Such high-brightness beams are very attractive for a compact ion source or an injector for RF accelerators. However in the case of foils scaling of the pulse repetition rate and improving shot-to-shot reproducibility is a serious challenge. CO2 laser-plasma interactions provide a possibility for using a debris free gas jet for target normal sheath acceleration of ions. Gas jets have the advantage of precise density control around the critical plasma density for 10 um pulses (1019 cm-3) and can be run at 1-10 Hz. The master oscillator–power amplifier CO2 laser system at the UCLA Neptune Laboratory is being upgraded to generate 1 J, 3 ps pulses at 1Hz. For this purpose, a new 8 atm CO2 module is used to amplify a 3 ps pulse to ~10 GW level. Final amplification is realized in a 1-m long TEA CO2 amplifier, for which the bandwidth necessary for 3 ps pulses is provided by the field broadening mechanism. Modeling of the pulse amplification shows that ~0.3 TW power is achievable that should be sufficient for producing 1-3 MeV H+ protons from the gas plasma.
 
 
MOP143 Enhanced Laser-Driven Ion Acceleration via Forward Raman Scattering in a Ramped Gas Target 358
 
  • S. Tochitsky, D.J. Haberberger, C. Joshi, W.B. Mori, F.S. Tsung
    UCLA, Los Angeles, California, USA
 
  Funding: This work is supported by DOE grant DE-FG02-92ER40727.
CO2 laser-plasma interactions provide a unique parameter space for using a gas jet for Target Normal Sheath Acceleration (TNSA) of ions instead of a thin foil target. The generation of 1-5 MeV protons from the interaction of a 3 ps TW CO2 laser pulse with a gas target with a peak density around the critical plasma density (1019 cm-3) has been studied by 2D particle-in-cell simulations. The proton acceleration in the preformed plasma, having similar to the gas jet symmetric, linearly ramped density distribution, occurs via formation of a sheath of hot electrons on the back surface of the target. The maximum energy of the hot electrons and, hence net acceleration of protons is mainly defined by Forward Raman scattering instability in the underdense part of the plasma. This mechanism of an additional heating of electrons is strongly affected by nonlinear laser-plasma interactions and results in the proton energy enhancement by more than an order of magnitude in comparison with the regular ponderomotive force scaling of TNSA. Forward directed ion beams from a gaseous target can find an application as a high-brightness ion source-injector.
 
 
TUOBN1 Laser Wakefield Acceleration Beyond 1 GeV using Ionization Induced Injection 707
 
  • K.A. Marsh, C.E. Clayton, C. Joshi, N. Lemos, W. Lu, W.B. Mori, A.E. Pak
    UCLA, Los Angeles, California, USA
  • F. Albert, T. Doeppner, C. Filip, D.H. Froula, S.H. Glenzer, B.B. Pollock, D. Price, J.E. Ralph
    LLNL, Livermore, California, USA
  • R.A. Fonseca, S.F. Martins
    Instituto Superior Tecnico, Lisbon, Portugal
  • L.O. Silva
    IPFN, Lisbon, Portugal
 
  Funding: Supported by DOE Grants No. DE-AC52-07NA27344, DE-FG03-92ER40727, DE-FG02-92ER40727, DE-FC02-07ER41500, DE-FG52-09NA29552, NSF Grants No. PHY-0936266, PHY-0904039 and FCT, Por., No. SFRH/BD/35749/2007
A series of laser wakefield accelerator experiments leading to electron energy exceeding 1 GeV are described. Theoretical concepts and experimental methods developed while conducting experiments using the 10 TW Ti:Sapphire laser at UCLA were implemented and transferred successfully to the 100 TW Calisto Laser System at the Jupiter Laser Facility at LLNL. To reach electron energies greater than 1 GeV with current laser systems, it is necessary to inject and trap electrons into the wake and to guide the laser for more than 1 cm of plasma. Using the 10 TW laser, the physics of self-guiding and the limitations in regards to pump depletion over cm-scale plasmas were demonstrated. Furthermore, a novel injection mechanism was explored which allows injection by ionization at conditions necessary for generating electron energies greater than a GeV. The 10 TW results were followed by self-guiding at the 100 TW scale over cm plasma lengths. The energy of the self-injected electrons, at 3x1018 cm-3 plasma density, was limited by dephasing to 720 MeV. Implementation of ionization injection allowed extending the acceleration well beyond a centimeter and 1.4 GeV electrons were measured.
 
slides icon Slides TUOBN1 [2.488 MB]  
 
TUOBN4 Plasma Wakefield Experiments at FACET 715
 
  • M.J. Hogan, R.J. England, J.T. Frederico, C. Hast, S.Z. Li, M.D. Litos, D.R. Walz
    SLAC, Menlo Park, California, USA
  • W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, S. Tochitsky
    UCLA, Los Angeles, California, USA
  • P. Muggli, S.F. Pinkerton, Y. Shi
    USC, Los Angeles, California, USA
 
  Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
FACET, the Facility for Advanced Accelerator and Experimental Tests, is a new facility being constructed in sector 20 of the SLAC linac primarily to study beam driven plasma wakefield acceleration beginning in summer 2011. The nominal FACET parameters are 23GeV, 3nC electron bunches compressed to ~20μm long and focused to ~10μm wide. The intense fields of the FACET bunches will be used to field ionize neutral lithium or cesium vapor produced in a heat pipe oven. Previous experiments at SLAC demonstrated 50GeV/m gradients in an 85cm field ionized lithium plasma where the interaction distance was limited by head erosion. Simulations indicate the lower ionization potential of cesium will decrease the rate of head erosion and increase single stage performance. The initial experimental program will compare the performance of lithium and cesium plasma sources with single and double bunches. Later experiments will investigate improved performance with a pre-ionized cesium plasma. The status of the experiments and expected performance are reviewed.
 
slides icon Slides TUOBN4 [13.080 MB]  
 
TUOBN5 A Proposed Experimental Test of Proton-Driven Plasma Wakefield Acceleration Based on CERN SPS 718
 
  • G.X. Xia, A. Caldwell
    MPI-P, München, Germany
  • W. An, C. Joshi, W. Lu, W.B. Mori
    UCLA, Los Angeles, California, USA
  • R.W. Assmann, F. Zimmermann
    CERN, Geneva, Switzerland
  • R.A. Fonseca, N.C. Lopes, J. Vieira
    Instituto Superior Tecnico, Lisbon, Portugal
  • C. Huang
    LANL, Los Alamos, New Mexico, USA
  • K.V. Lotov
    BINP SB RAS, Novosibirsk, Russia
  • P. Muggli
    USC, Los Angeles, California, USA
  • A.M. Pukhov
    HHUD, Dusseldorf, Germany
  • L.O. Silva
    IPFN, Lisbon, Portugal
 
  Proton-driven plasma wakefield acceleration (PDPWA) has been proposed as an approach to accelerate electron beam to TeV energy regime in a single passage of plasma channel. An experimental test is recently proposed to demonstrate the capability of PDPWA by using proton beams from the CERN SPS. The preparation of experiment is introduced. The particle-in-cell simulation results based on realistic beam parameters are presented.  
slides icon Slides TUOBN5 [2.208 MB]  
 
TUOBN6 Production of 25 MeV Protons in CO2 Laser-Plasma Interactions in a Gas Jet 721
 
  • D.J. Haberberger, C. Gong, C. Joshi, S. Tochitsky
    UCLA, Los Angeles, California, USA
 
  Funding: This work is supported by DOE grant DE-FG02-92ER40727 and NSF grant PHY-0936266
At the Neptune Laboratory at UCLA, we have developed a high-power CO2 MOPA laser system which produces world record multi-terawatt 10um pulses. The CO2 laser pulses consist of a train of 3ps pulses separated by 18ps, each with a peak power of up to 4TW and a total pulse train energy of ~100J. These relativistic laser pulses are applied for Laser Driven Ion Acceleration in an H2 gas jet operated around the critical density of 1019 cm-3 for 10um light using the Target Normal Sheath Acceleration mechanism. The laser is focused into the gas jet reaching a normalized field strength of a0~2 in vacuum. For these conditions, protons with a maximum energy of 25MeV and a narrow energy spread of ΔE/E < 1% are recorded. Initial analysis of these experimental results shows a stronger scaling of the proton energy than that predicted from the ponderomotive force, and highlights the importance of an accumulated effect of multiple CO2 laser pulses lasting over 100ps. The temporal dynamics of the overdense plasma slab are probed with a picosecond 532nm pulse and the results will be discussed.
 
 
WEOBS3 The Effects of a Density Mismatch in a Two-State LWFA 1421
 
  • B.B. Pollock, F. Albert, C. Filip, D.H. Froula, S.H. Glenzer, J.E. Ralph
    LLNL, Livermore, California, USA
  • C.E. Clayton, C. Joshi, K.A. Marsh, J. Meinecke, A.E. Pak, J.L. Shaw
    UCLA, Los Angeles, California, USA
  • K.L. Herpoldt
    Oxford University, Physics Department, Oxford, Oxon, United Kingdom
  • G.R. Tynan
    UCSD, La Jolla, California, USA
 
  Funding: Work performed under U.S. DOE Contract DE-AC52-07NA27344 and was partially funded by the Laboratory Directed Research and Development Program under project tracking code 06-ERD-056.
A two-stage Laser Wakefield Accelerator (LWFA) has been developed, which utilizes the ionization induced injection mechanism to produce high energy, narrow energy spread electron beams when the electron density is equal in both stages. However, when the densities are not equal these high quality beams are not observed. As the electron density varies across the interface between the adjacent stages the size of the ion cavity is expected to change; this results in either a reduction of the peak electron energy (for a density decrease), or in the exclusion of previously trapped charge from the first wake period (for a density increase). The latter case can be overcome if the interaction length before the density interface exceeds a threshold determined by the densities in each stage, and may provide a mechanism for enhanced energy gain.