WEA —  Wednesday - Early Morning   (28-Aug-19   09:00—10:30)
Chair: B.E. Carlsten, LANL, Los Alamos, New Mexico, USA
Paper Title Page
WEA01 Overview of CW RF Guns for Short Wavelength FELs 290
 
  • H.J. Qian
    DESY Zeuthen, Zeuthen, Germany
  • E. Vogel
    DESY, Hamburg, Germany
 
  Hard X-ray FELs (XFELs) operating with pulsed RF provide unprecedented peak brilliance for scientific research. Operating the accelerators with CW RF improves the flexibility w.r.t. the available time structure for experiments and opens the next frontier of average brilliance. One of the challenges of CW XFELs is the electron source, which requires both CW operation and highest possible beam quality allowing lasing at shortest wavelengths. The CW mode technically constraints the gun acceleration gradient, which is one of the keys to electron source brightness, so R&D is devoted to CW gun improvements since decades. In this contribution, the worldwide development status of CW RF guns, both normal conducting and superconducting, is reviewed.  
slides icon Slides WEA01 [16.329 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA01  
About • paper received ※ 25 August 2019       paper accepted ※ 07 November 2019       issue date ※ 05 November 2019  
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WEA02
State-of-the-Art Photocathodes and New Developments  
 
  • N.A. Moody, J. Smedley
    LANL, Los Alamos, New Mexico, USA
 
  Funding: Laboratory Directed Research and Development performed at Los Alamos National Laboratory under project number 20150394DR.
Development of photoemission electron sources for advanced light sources such as X-ray Free Electron Lasers (xFEL), ultra-fast electron diffraction (UED), and low-light sensor applications has motivated a comprehensive engineered-material approach integrating predictive computational physics models, advanced nano-synthesis methods and characterization with in-situ correlated study of photoemission performance and properties [1]. Techniques such as compositionally graded stoichiometry, heterostructured architectures, and quantum features, allowing for enhanced optoelectronic properties [2]. These methods influence the mechanisms of photoemission but have not, until recently, been applied toward photocathode applications [3]. Recent results from a growing collaboration effort involving advanced synthesis, X-ray synchrotron characterization, and modeling efforts show the efficacy of these approaches. Highlights of these studies, including predictions and experimental data, are presented as well as future plans to exploit controlled functionality of nanomaterials for photocathodes and other optoelectronic devices.
[1] N. Moody, K. Jensen et al., Phys. Rev. Appl. 10, 047002 (2018)
[2] A. Shabaev and A. Efros, Nano Lett. 13, 5454 (2013)
[3] M. Gaowei, Z. Ding et al., APL Materials 5, 116104 (2017)
 
slides icon Slides WEA02 [10.245 MB]  
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WEA03
Emittance Budget in the Transition Regime Between Linear Emission and Space Charge Dominated Photoemission  
 
  • Y. Chen, M. Krasilnikov, H.J. Qian, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  Free electron laser based X-ray facilities require high brightness accelerators which entails minimization of the beam emittance in all planes for a fixed bunch charge. Since the lowest achievable emittance of linac based accelerators is set at the injectors already, emittance optimization at the injector exit needs to carefully budget the contributions from the space charge and rf forces as well as the intrinsic cathode contribution. The optimization of normalized transverse emittance at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) has routinely found the smallest possible emittance for a fixed bunch charge in a so-called transition regime of photoemission. In such a regime, high space charge density of the beam significantly contributes to the phase space formation. Strong space charge fields during the emission process alter the cathode physics thereby changing the emittance budget distribution. Based on an advanced beam dynamics modeling approach, we analyze each decomposed contribution of the measured emittance for understanding the optimization scheme in the transition regime between linear and space charge dominated emission. Obtained results will be presented.  
slides icon Slides WEA03 [1.918 MB]  
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WEA04 Growing and Characterization of Cs2Te Photocatodes with Different Thicknesses at INFN LASA 297
 
  • L. Monaco, P. Michelato, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • G. Guerini Rocco, C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
 
  The INFN LASA group has a long standing experience in the production of cesium telluride photocathodes for high brightness photoinjectors. The well-established recipe relies on the deposition of a typical amount of 10 nm of Te, followed by the Cs deposition until reaching the maximum QE. Nevertheless, for improving the understanding of photocathode properties, we are investigating the effect of Te thickness on the growing process, evaluating photocathode optical properties and quantum efficiency during the growing process and on the final film. These photocathodes will be then operated and analyzed in the real environment of the RF Gun at the PITZ facility in DESY Zeuthen, to estimate their impact on the electron beam properties.  
slides icon Slides WEA04 [15.703 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA04  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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