Author: Joshi, C.
Paper Title Page
Highly Spin-Polarized Multi-GeV Sub-Femtosecond Electron Beams Generated From Single-Species Plasma Photocathodes  
  • Z. Nie, C. Joshi, F. Li, K.A. Marsh, D. Matteo, W.B. Mori, N. Nambu, F.S. Tsung, Y.P. Wu, C. Zhang
    UCLA, Los Angeles, California, USA
  • W. An
    BNU, Haidian District Beijing, People’s Republic of China
  • F. Morales, S. Patchkovskii, O. Smirnova
    MBI, Berlin, Germany
  Funding: DOE Grant No. DE-SC0010064; DOE through a SciDAC FNAL Subcontract No. 644405; NSF Grants No. 1734315, No. 1806046 and No. 2108970; ONR MURI (4-442521-JC-22891); and NSFC Grant No. 12075030
High-gradient and high-efficiency acceleration in plasma-based accelerators has been demonstrated, showing its potential as the building block for a future collider operating at the energy frontier of particle physics. However, generating and accelerating the required spin-polarized beams in such a collider using plasma-based accelerators has been a long-standing challenge. Here we show that the passage of a highly relativistic, high-current electron beam through a single-species (ytterbium) vapor excites a nonlinear plasma wake by primarily ionizing the two outer 6s electrons. Further photoionization of the resultant Yb2+ ions by a circularly polarized laser injects the 4f14 electrons into this wake generating a highly spin-polarized beam. Combining time-dependent Schrodinger equation simulations with particle-in-cell simulations, we show that a sub-femtosecond, high-current (4 kA) electron beam with up to 56% net spin polarization can be generated and accelerated to 15 GeV in just 41 cm. This relatively simple scheme solves the perplexing problem of producing spin-polarized relativistic electrons in plasma-based accelerators.
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Characterization of the Fields Inside the CO2-Laser-Driven Wakefield Accelerators Using Relativistic Electron Beams  
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
  • M. Babzien, M.G. Fedurin, K. Kusche, M.A. Palmer, I. Pogorelsky, M.N. Polyanskiy
    BNL, Upton, New York, USA
  • M. Downer, R. Zgadzaj
    The University of Texas at Austin, Austin, Texas, USA
  • A.S. Gaikwad, V. Litvinenko, N. Vafaei-Najafabadi
    Stony Brook University, Stony Brook, USA
  • C. Joshi, W.B. Mori, C. Zhang
    UCLA, Los Angeles, California, USA
  • R. Kupfer
    LLNL, Livermore, USA
  • V. Samulyak
    SBU, Stony Brook, USA
  The CO2 laser at the Accelerator Test Facility of Brookhaven National Laboratory is a unique source generating 2-ps-long, multi-TW pulses in the mid-IR regime. This rapidly evolving system opens an opportunity for the generation of large bubbles in low-density plasmas (~1016 cm-3) that are ideal for acceleration of externally injected electron beams. A new generation of diagnostic tools is needed to characterize the fields inside such structures and to improve the means of external injection. In recent years, the electron beam probing technique has shown to be successful in direct visualization of the plasma wakefields. Here we present a new method utilizing the electron beam probing and Transmission Electron Microscopy (TEM) grids that will allow us to selectively illuminate different portions of the wake and to characterize the electric field strength within the wake based on the location of the focal point of the probe beamlets. The analytical evaluation of the approach and supporting simulation results will be presented and discussed.  
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