Author: Musumeci, P.
Paper Title Page
MOZD2 Preliminary Study of a High Gain THz FEL in a Recirculating Cavity 30
  • A.C. Fisher, P. Musumeci
    UCLA, Los Angeles, USA
  The THz gap is a region of the electromagnetic spectrum where high average and peak power radiation sources are scarce while at the same time scientific and industrial applications are growing in demand. Free-electron laser coupling in a magnetic undulator is one of the best options for radiation generation in this frequency range, but slippage effects require the use of relatively long and low current electron bunches to drive the THz FEL, limiting amplification gain and output peak power. Here we use a circular waveguide in a 0.96 m strongly tapered helical undulator to match the radiation and e-beam velocities, allowing resonant energy extraction from an ultrashort 200 pC 5.5 MeV electron beam over an extended distance. E-beam energy measurements, supported by energy and spectral measurement of the THz FEL radiation, indicate an average energy efficiency of ~ 10%, with some particles losing > 20% of their initial kinetic energy.  
slides icon Slides MOZD2 [7.005 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD2  
About • Received ※ 04 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 13 August 2022
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TUXD6 Dual Radiofrequency Cavity Based Monochromatization for High Resolution Electron Energy Loss Spectroscopy 278
  • A.V. Kulkarni, P.E. Denham, A. Kogar, P. Musumeci
    UCLA, Los Angeles, USA
  Reducing the energy spread of electron beams can enable breakthrough advances in electron energy loss spectroscopic investigations of solid state samples where characteristic excitations typically have energy scales on the order of meV. In conventional electron sources the energy spread is limited by the emission process and typically on the order of a fraction of an eV. State-of-the-art energy resolution can only be achieved after significant losses in the monochromatization process. Here we propose to take advantage of photoemission from ultrashort laser pulses (~40 fs) so that after a longitudinal phase space manipulation that trades pulse duration for energy spread, the energy spread can be reduced by more than one order of magnitude. The scheme uses two RF cavities to accomplish this goal and can be implemented on a relatively short (~ 1m) beamline. Analytical predictions and results of 3D self consistent beam dynamics simulations are presented to support the findings.  
slides icon Slides TUXD6 [1.461 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUXD6  
About • Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 18 August 2022
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TUYD3 The Quest for the Perfect Cathode 281
  • J.W. Lewellen, J. Smedley, T. Vecchione
    SLAC, Menlo Park, California, USA
  • D. Filippetto
    LBNL, Berkeley, California, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
  • J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • P. Musumeci
    UCLA, Los Angeles, California, USA
  Funding: U.S. Department of Energy.
The next generation of free electron lasers will be the first to see the performance of the laser strongly dependent on the materials properties of the photocathode. A new injector proposed for the LCLS-II HE is an example of this revolution, with the goal of increasing the photon energy achievable by LCLS-II to over 20 keV. We must now ask, what is the optimal cathode, temperature, and laser combination to enable this injector? There are many competing requirements. The cathode must be robust enough to operate in a superconducting injector, and must not cause contamination of the injector. It must achieve sufficient charge at high repetition rate, while minimizing the emittance. The wavelength chosen must minimize mean transverse energy while maintaining tolerable levels of multi-photon emission. The cathode must be capable of operating at high (~30 MV/m) gradient, which puts limits on both surface roughness and field emission. This presentation will discuss the trade space for such a cathode/laser combination, and detail a new collaborative program among a variety of institutions to investigate it.
slides icon Slides TUYD3 [1.632 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD3  
About • Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 14 August 2022 — Issue date ※ 26 September 2022
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TUPA77 X-Band Harmonic Longitudinal Phase Space Linearization at the PEGASUS Photoinjector 508
  • P.E. Denham, P. Musumeci, A. Ody
    UCLA, Los Angeles, USA
  Due to the finite bunch length, photoemitted electron beams sample RF-nonlinearities that lead to energy-time correlations along the bunch temporal profile. This is an important effect for all applications where the projected energy spread is important. In particular, for time-resolved single shot electron microscopy, it is critical to keep the beam energy spread below 1·10-4 to avoid chromatic aberrations in the lenses. Higher harmonic RF cavities can be used to compensate for the RF-induced longitudinal phase space nonlinearities. Start-to-end simulations suggest that this type of compensation can reduce energy spread to the 1·10-5 level. This work is an experimental study of x-band harmonic linearization of a beam longitudinal phase space at the PEGASUS facility, including developing high-resolution spectrometer diagnostics to verify the scheme.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA77  
About • Received ※ 25 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 10 August 2022
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Current Status of Developing an Ultrafast Electron Microscope  
  • X. Yang, T.V. Shaftan, V.V. Smaluk, Y. Zhu
    BNL, Upton, New York, USA
  • P. Musumeci
    UCLA, Los Angeles, California, USA
  • W. Wan
    ShanghaiTech University, Shanghai, People’s Republic of China
  Recent studies of ultrafast electron microscopy (UEM) techniques show the use of short bunches of relativistic electrons are promising for the development of a new instrument for imaging samples of various materials. Compared to conventional electron microscopes, the main advantage of UEMs with the electron energy of a few MeV is the possibility to study thick samples. We will discuss the progress of UEM design to date, the principal challenges on the way to a high resolution, and possible methods for their mitigation including the design of low-aberration magnetic optics, RF and mechanical subsystems with high stability, and precise collimation of electrons scattered in the samples.  
slides icon Slides WEZE1 [11.286 MB]  
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WEPA44 Compact Inter-Undulator Diagnostic Assembly for TESSA-515 732
  • T.J. Hodgetts, R.B. Agustsson, Y.C. Chen, A.Y. Murokh, M. Ruelas
    RadiaBeam, Santa Monica, California, USA
  • P.E. Denham, A.C. Fisher, J. Jin, P. Musumeci, Y. Park
    UCLA, Los Angeles, USA
  Funding: DOE grant DE-SC0009914, DE-SC0018559, and DE-SC0017102.
Beamline space is a very expensive and highly sought-after commodity, which makes the creation of compact integrated optics and diagnostics extremely valuable. The FAST- GREENS experimental program aims at demonstrating 10 % extraction efficiency from a relativistic electron beam using four helical undulators operating in the high gain TESSA regime. The inter-undulator gap needs to be as short as possible (17 cm in the current plans) to maximize the output power. Within this short distance, we needed to fit two focusing quadrupoles, a variable strength phase shifter, a transverse profile monitor consisting of a YAG-OTR combination for co-aligning the electron beam and laser, and an ion pump. By making the quadrupoles tunable with a variable gradient, in combination with vertical displacement, we can meet the optics requirements of matching the beam transversely to the natural focusing of the undulators. The two quadrupoles in conjunction with the electromagnetic dipole also serve as a phase shifter to realign the radiation and the bunching before each undulator section. This paper will discuss the mechanical design of this inter-undulator break section and its components.
poster icon Poster WEPA44 [0.752 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA44  
About • Received ※ 27 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 11 August 2022
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THZE4 Experimental Characterization of Gas Sheet Transverse Profile Diagnostic 907
  • N. Burger, G. Andonian, D.I. Gavryushkin, T.J. Hodgetts, A.-L.M.S. Lamure, M. Ruelas
    RadiaBeam, Santa Monica, California, USA
  • N.M. Cook, A. Diaw
    RadiaSoft LLC, Boulder, Colorado, USA
  • P.E. Denham, P. Musumeci, A. Ody
    UCLA, Los Angeles, USA
  • N.P. Norvell
    UCSC, Santa Cruz, California, USA
  • C.P. Welsch, M. Yadav
    The University of Liverpool, Liverpool, United Kingdom
  • C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  Transverse profile diagnostics for high-intensity beams require solutions that are non-intercepting and single-shot. In this paper, we describe a gas-sheet ionization diagnostic that employs a precision-shaped, neutral gas jet. As the high-intensity beam passes through the gas sheet, neutral particles are ionized. The ionization products are transported and imaged on a detector. A neural-network based reconstruction algorithm, trained on simulation data, then outputs the initial transverse conditions of the beam prior to ionization. The diagnostic is also adaptable to image the photons from recombination. Preliminary tests at low energy are presented to characterize the working principle of the instrument, including comparisons to existing diagnostics. The results are parametrized as a function of beam charge, spot size, and bunch length.  
slides icon Slides THZE4 [2.051 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THZE4  
About • Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 09 October 2022
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