Author: Robles, R.
Paper Title Page
MOPOTK045 Generation of High Emittance Ratios in High Charge Electron Beams at FACET-II 560
 
  • O. Camacho
    UCLA, Los Angeles, USA
  • A. Halavanau, R. Robles
    SLAC, Menlo Park, California, USA
 
  Funding: DE-SC0009914
Experiments foreseen at FACET-II, including dielectric plasma wakefield acceleration and linear collider tests, call for electron beams with highly asymmetric transverse emittances - so called "flat beams". A canonical recipe for the generation of such beams is injecting a magnetized beam at a waist into an appropriately tuned skewed quadrupole triplet channel. However, due to the intense non-linear space-charge forces that dominate nC bunches, this method presents difficulties in maintaining the flatness. We proceed with generalized round-to-flat-beam (RTFB) transformation, which takes into account the non-negligible divergence of the beam at the channel entrance, using a quartet of skewed quadrupoles. Our analytical results are further optimized in ELEGANT and GPT simulation programs and applied to the case of the FACET-II beamline. Non-ideal cathode spot distributions obtained from recent FACET-II experiments are used for accurate numerical modeling. Tolerances to quadrupole strengths and alignment errors are also considered, with an eye towards developing hardware specifications.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-MOPOTK045  
About • Received ※ 03 June 2022 — Revised ※ 24 June 2022 — Accepted ※ 25 June 2022 — Issue date ※ 09 July 2022
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TUPOPT039 Characterization of Diamond with Buried Boron-Doped Layer Developed for Q-Switching an X-Ray Optical Cavity 1097
 
  • R.A. Margraf, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, G. Marcus, M.L. Ng, A.R. Robert, R. Robles, T. Sato, D. Zhu
    SLAC, Menlo Park, California, USA
  • Z. Huang, F. Ke, R. Robles, Y. Zhong
    Stanford University, Stanford, California, USA
  • S.-K. Mo, Y. Zhong
    LBNL, Berkeley, California, USA
  • P. Pradhan
    ANL, Lemont, Illinois, USA
  • A.R. Robert
    MAX IV Laboratory, Lund University, Lund, Sweden
  • M.D. Ynsa
    UAM, Madrid, Spain
 
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
X-ray Free-Electron Laser Oscillators (XFELOs) and X-ray Regenerative Amplifier FELs (XRAFELs) are currently in development to improve longitudinal coherence and spectral brightness of XFELs. These schemes lase an electron beam in an undulator within an optical cavity to produce X-rays. X-rays circulate in the cavity and interact with fresh electron bunches to seed the FEL process over multiple passes, producing progressively brighter and more spectrally pure X-rays. Typically, the optical cavities used are composed of Bragg-reflecting mirrors to provide high reflectivity and spectral filtering. This high reflectivity necessitates special techniques to out-couple X-rays from the cavity to deliver them to users. One method involves "Q-switching" the cavity by actively modifying the reflectivity of one Bragg-reflecting crystal. To control the crystal lattice constant and thus reflectivity, we use an infrared laser to heat a buried boron layer in a diamond crystal. Here, we build on earlier work in Krzywinski et al.* and present the current status of our Q-switching diamond, including implantation with 9 MeV boron ions, annealing, characterization and early tests.
*Krzywinski et al., "Q-switching of X-Ray Optical Cavities by using Boron Doped Buried Layer under a Surface of a Diamond Crystal," Proceedings of FEL2019, Hamburg, Germany, TUP033, 2019.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT039  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 08 July 2022
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TUPOPT044 High-Power Attosecond Pulses via Cascaded Amplification 1101
 
  • P.L. Franz, Z.H. Guo, S. Li, R. Robles
    Stanford University, Stanford, California, USA
  • D.K. Bohler, D.B. Cesar, X. Cheng, J.P. Cryan, T.D.C. Driver, J.P. Duris, A. Kamalov, S. Li, A. Marinelli, R. Obaid, R. Robles, N.S. Sudar, A.L. Wang, Z. Zhang
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by US Department of Energy Contracts No. DE-AC02-76SF00.
The timescale for electron motion in molecular systems is on the order of hundreds of attoseconds, and thus the time-resolved study of electronic dynamics requires a source of sub-femtosecond x-ray pulses. Here we report the experimental generation of sub-femtosecond duration soft x-ray free electron laser (XFEL) pulses with hundreds of microjoules of energy using fresh-slice amplification in two cascaded stages at the Linac Coherent Light Source. In the first stage, an enhanced self-amplified spontaneous emission (ESASE) pulse is generated using laser-shaping of the electron beam at the photocathode*. The electron bunch is then delayed relative to the pulse by a magnetic chicane, allowing the radiation to slip onto a fresh slice of the bunch, which amplifies the ESASE pulse in the second cascade stage. Angular streaking** characterizes the experimental pulse durations as sub-femtosecond at ~465 eV in the experiment.
* Zhang, Z. et al. New J. Phys. 22 (2020)
** Li, S. et al. Optics Express 26.4 (2018): 4531-4547.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT044  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 21 June 2022
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WEOZGD2
Status and Prospects for the Plasma-Driven Attosecond X-Ray (PAX) Experiment at FACET-II  
 
  • C. Emma, R.M. Hessami, K. Larsen, A. Marinelli, R. Robles
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02- 76SF00515.
Plasma-driven light source development has recently made significant progress with the demonstration of plasma-FEL gain and the work of multiple facilities towards plasma-FEL development *. In this paper, we report on the status and prospects for one-such plasma-driven light source effort, the Plasma-driven Attosecond X-ray (PAX) experiment at FACET-II ** . This unique experimental thrust seeks to generate 100-attosecond long electron beams using plasma accelerators and use these beams as drivers for an attosecond X-ray source. This approach is motivated by the possibility to generate ultra-short high power attosecond X-ray pulses, as well as the order-of-magnitude increased tolerances of this method to emittance, energy spread and pointing jitter compared to a plasma-driven XFEL starting from noise. We present recent experimental developments in the process of demonstrating this concept at FACET-II and discuss potential extensions of this method to scale towards shorter wavelengths in the future.
* W. Wang et al Nature 595, 516 2021; R. Pompili Proc. of EAAC 2021; C. Emma et al High Power Laser Science and Engineering, 2021, Vol. 9, e57,
** C. Emma et al APL Photonics 6, 076107 2021
 
slides icon Slides WEOZGD2 [5.088 MB]  
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WEPOST048 Excitation of Very High Gradient Plasma Wakefields From Nanometer Scale Beams 1806
 
  • P. Manwani, H.S. Ancelin, G. Andonian, D.R. Chow, N. Majernik, J.B. Rosenzweig, M. Yadav
    UCLA, Los Angeles, California, USA
  • G. Andonian
    RadiaBeam, Marina del Rey, California, USA
  • R. Robles
    SLAC, Menlo Park, California, USA
  • M. Yadav
    The University of Liverpool, Liverpool, United Kingdom
  • M. Yadav
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  Funding: This work was performed with the support of the US Department of Energy under Contract No. DESC0009914.
The plasma based terawatt attosecond project at SLAC, termed PAX, offers near mega-Ampere beams that could be used to demonstrate plasma wakefield acceleration at very high gradients (TV/m). The beam has a large aspect ratio which allows it to be used at high densities since the longitudinal beam size is lower than the plasma skin depth. This beam can be focused using a permanent magnitude quadrupole (PMQ) triplet to further reduce its transverse size. Since the beam is extremely short compared to the plasma skin depth, it behaves like a delta-function perturbation to the plasma. This reduces the expected focusing effect of the ion column and simulations show that only the tail of the beam is notably focused and decelerated. This scenario is investigated with attendant experimental considerations discussed. The creation of the witness beam by the deceleration of the tail of the beam is also discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-WEPOST048  
About • Received ※ 08 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 29 June 2022
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WEPOTK064 Generating Sub-Femtosecond Electron Beams at Plasma Wakefield Accelerators 2217
 
  • R. Robles, C. Emma, R.M. Hessami, K. Larsen, A. Marinelli
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by US Department of Energy Contracts No. DE-AC02-76SF00515 and by the DOE, Laboratory Directed Research and Development program at SLAC, under contract DE-AC02-76SF00515.
The Plasma-driven Attosecond X-ray source (PAX) project at FACET-II aims to produce attosecond EUV/soft x-ray pulses with milijoule-scale pulse energy via nearly coherent emission from pre-bunched electron beams. In the baseline approach*, a beam is generated using the density downramp injection scheme with a percent-per-micron chirp and 1e-4 scale slice energy spread. Subsequent compression yields a current spike of just 100 as duration which can emit 10 nm light nearly coherently due to its strong pre-bunching. In this work, we report simulation studies of a scheme to generate similarly short beams without relying on plasma injection. Instead, we utilize a high-charge beam generated at an RF photocathode, with its tail acting as the witness bunch for the wake. The witness develops a percent-per-micron chirp in the plasma which is then compressible downstream. The final bunch length demonstrated here is as short as 100 nm, and is limited primarily by emittance effects. The configurations studied in this work are available for experimental testing at existing PWFA facilities such as FACET-II.
*APL Photonics 6, 076107 (2021)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-WEPOTK064  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 16 June 2022
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WEPOTK065 Revisiting Intrabeam Scattering for Laminar Beams 2221
 
  • R. Robles, Z. Huang, A. Marinelli
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by US Department of Energy Contracts No. DE-AC02-76SF00515
Intrabeam scattering (IBS) is becoming an increasingly important effect in the design of high-brightness linear electron accelerators due to the ever-increasing transverse brightness of beams produced from radiofrequency photoinjectors. The existing theory describing the energy spread growth rate due to IBS was derived in the context of circular machines where the beam particles are frequently and randomly colliding, and therefore should only be applied to non-laminar, emittance dominated flow. This is not the case in the injector portion of a linear accelerator, where the beam is space-charge dominated and the flow is laminar. The different nature of the microscopic motion in the two cases demands a reevaluation of the applicability of IBS theory to the photoinjector. In this work, we present a simple analytic model for energy spread growth during perfectly laminar flow and show that it matches well to point-to-point multiparticle simulations. In this way we demonstrate that stochastic energy spread growth in laminar beams is more attributable to the initial random placement of the particles in the bunch rather than the traditional temperature rearrangement mechanism of IBS.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-WEPOTK065  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 08 July 2022
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TUPOPT047 Progress Report on Population Inversion X-Ray Laser Oscillator at LCLS 1107
 
  • A. Halavanau, R. Alonso-Mori, A. Aquila, U. Bergmann, F.-J. Decker, F. Fuller, M. Liang, A.A. Lutman, R.A. Margraf, R.H. Paul, C. Pellegrini
    SLAC, Menlo Park, California, USA
  • R. Ash, N.B. Welke
    UW-Madison/PD, Madison, Wisconsin, USA
  • A.I. Benediktovitch
    DESY, Hamburg, Germany
  • S.C. Krusic
    JSI, Ljubljana, Slovenia
  • N. Majernik, P. Manwani, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  • R. Robles
    Stanford University, Stanford, California, USA
  • N. Rohringer
    Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
 
  We report the progress in the design and construction of a population inversion x-ray laser oscillator (XLO) using LCLS as an x-ray laser pump, being developed by a SLAC, CFEL, University of Hamburg (Germany), University of Wisconsin, Josef Stefan Institute (Slovenia) and UCLA collaboration. In this proceeding, we will present the latest XLO design and numerical simulations substantiated by our first experimental results. In our next experimental step XLO will be tested on the Coherent X-ray Imaging (CXI) end-station at LCLS as a two pass Regenerative Amplifier operating at the Copper Kα1 photon energy of 8048 eV. When built, XLO will generate fully coherent transform limited pulses with about 50 meV FWHM bandwidth. We expect the XLO will pave the way for new user experiments, e.g. in inelastic x-ray scattering, parametric down conversion, quantum science, x-ray interferometry, and external hard x-ray XFEL seeding.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT047  
About • Received ※ 12 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 24 June 2022
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