Keyword: SRF
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TUPAF19 pyaopt Optimization Suite and its Applications to an SRF Cavity Design for UEMs gun, simulation, cavity, electron 229
  • A. Liu, P.V. Avrakhov, R.A. Kostin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • C.-J. Jing
    Euclid Beamlabs LLC, Bolingbrook, USA
  Funding: DOE SBIR
In order to achieve sharp, high resolution real-time imaging, electrons in a MeV UEM (ultrafast electron microscope) beamline need to minimize instabilities. The Superconducting RF (SRF) photocathode gun is a promising candidate to produce highly stable electrons for UEM/UED applications. It operates in an ultrahigh Q, CW mode, and dissipates a few watts of RF power, which make it possible to achieve a 10s ppm level of beam stability by using modern RF control techniques. In order to find the best performance of the gun design, an optimization procedure is required. pyaopt is a Python-based optimization suite that supports multi-objective optimizations using advanced algorithms. In this paper, the novel SRF photogun design and its optimizations through pyaopt and Astra’s beam simulations will be discussed.
DOI • reference for this paper ※  
About • paper received ※ 22 October 2018       paper accepted ※ 15 December 2018       issue date ※ 26 January 2019  
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TUPAG04 Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections cavity, HOM, linac, cryomodule 265
  • A. Lunin, T.N. Khabiboulline, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  Funding: Work is supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy
The superconducting radio frequency (SRF) technology is progressing rapidly over last decades toward high accelerating gradients and low surface resistance making feasible the particle accelerators operation with high beam currents and long duty factors. However, the coherent RF losses due to high order modes (HOMs) excitation becomes a limiting factor for these regimes. In spite of the operating mode, which is tuned separately, the parameters of HOMs vary from one cavity to another due to finite mechanical tolerances during cavities fabrication. It is vital to know in advance the spread of HOM parameters in order to predict unexpected cryogenic losses, overheating of beam line components and to keep stable beam dynamics. In this paper we present the method of generating the unique cavity geometry with imperfections while preserving operating mode frequency and field flatness. Based on the eigenmode spectrum calculation of series of randomly generated cavities we can accumulate the data for the evaluation the HOM statistics. Finally, we describe the procedure for the estimation of the probability of the resonant HOM losses in the SRF resonators. The study of these effects leads to specifications of SC cavity and cryomodule and can significantly impact on the efficiency and reliability of the machine operation
slides icon Slides TUPAG04 [1.810 MB]  
DOI • reference for this paper ※  
About • paper received ※ 15 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAG07 Efficient Computation of Lossy Higher Order Modes in Complex SRF Cavities Using Reduced Order Models and Nonlinear Eigenvalue Problem Algorithms cavity, GUI, HOM, impedance 270
  • H.W. Pommerenke, J. Heller, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  Superconducting radio frequency (SRF) cavities meet the demanding performance requirements of modern accelerators and high-brilliance light sources. For the operation and design of such resonators, a very precise knowledge of their electromagnetic resonances is required. The non-trivial cavity shape demands a numerical solution of Maxwell’s equations to compute the resonant eigenfrequencies, eigenmodes, and their losses. For large and complex structures this is hardly possible on conventional hardware due to the high number of degrees of freedom required to obtain an accurate solution. In previous work it has been shown that the considered problems can be solved on workstation computers without extensive simplification of the structure itself by a combination of State-Space Concatenation (SSC) and Newton iteration to solve the arising nonlinear eigenvalue problem (NLEVP). First, SSC is applied to the complex, closed and thus lossless RF structure. SSC employs a combination of model order reduction and domain decomposition, greatly reducing the computational effort by effectively limiting the considered frequency domain. Next, a perturbation approach based on SSC is used to describe the resonances of the same geometry subject to external losses. This results in a NLEVP which can be solved efficiently by Newton’s method. In this paper, we expand the NLEVP solution algorithm by a contour integral technique, which increases the completeness of the solution set.  
slides icon Slides TUPAG07 [11.204 MB]  
DOI • reference for this paper ※  
About • paper received ※ 18 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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