Keyword: electromagnetic-fields
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THPAF036 Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions impedance, vacuum, coupling, factory 3040
  • M. Migliorati, L. Palumbo
    Sapienza University of Rome, Rome, Italy
  • N. Biancacci
    CERN, Geneva, Switzerland
  • M. Migliorati, L. Palumbo
    INFN-Roma1, Rome, Italy
  • V.G. Vaccaro
    Naples University Federico II and INFN, Napoli, Italy
  Funding: Work supported by the CERN PS-LIU project
The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultra-relativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultra-relativistic particles. Even if some of the results, in particular in the ultra-relativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multi-layer vacuum chamber with different conductivities and of elliptic cross section.
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THPAK078 GPT-CSR: a New Simulation Code for CSR Effects radiation, simulation, emittance, linac 3414
  • S.B. van der Geer, M.J. de Loos
    Pulsar Physics, Eindhoven, The Netherlands
  • A.D. Brynes, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • I.D. Setija, P.W. Smorenburg
    ASML Netherlands B.V., Veldhoven, The Netherlands
  For future applications of high-brightness electron beams, including the design of next generation FEL's, correct simulation of Coherent Synchrotron Radiation (CSR) is essential as it potentially degrades beam quality to unacceptable levels. However, the long interaction lengths compared to the bunch length, numerical cancellation, and difficult 3D retardation conditions make accurate simulation of CSR effects notoriously difficult. To ease the computational burden, CSR codes often make severe simplifications such as an ultra-relativistic bunch travelling on a prescribed reference trajectory. Here we report on a new CSR model implemented in the General Particle Tracer (GPT) code that avoids most of the usual assumptions: It directly evaluates the Liénard'Wiechert potentials based on the stored history of the beam. It makes no assumptions about reference trajectories, and also takes into account the transverse size of the beam. Example results demonstrating normalised emittance growth in the first bunch compressor of FERMI@Elettra are presented.  
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THPAK086 A 2D Steady-State Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree space-charge, gun, cathode, distributed 3431
  • A.R. Gold, A. R. Gold, S.G. Tantawi
    SLAC, Menlo Park, California, USA
  Correctly and rapidly simulating the steady-state interaction between particle beams and electromagnetic fields is crucial to the design and optimization of accelerator and radiofrequency (RF) source components. Iteratively solving for the self-consistent interaction between particles and fields can prove challenging and highly susceptible to numerical noise and mesh induced instabilities. We present herein two new approaches to solving the self-consistent trajectories of particles in the presence of external and self fields. The first method reformulates the integrated self field contribution as a path integral. The second method uses a hybrid Eulerian framework and produces an interpolated continuous current density, resulting in 1-2 orders of magnitude fewer particles required to obtain an accurate solution. We conclude with benchmarking results which show this method is as accurate as state of the art PIC solvers, while running 80-120X faster.  
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THPAL015 Evaluation of superconducting characteristics on the thin-film structure by NbN and Insulator coatings on pure Nb substrate cavity, embedded, SRF, radio-frequency 3653
  • R. Katayama, Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • C.Z. Antoine
    CEA/IRFU, Gif-sur-Yvette, France
  • A. Four
    CEA/DRF/IRFU, Gif-sur-Yvette, France
  • H. Hayano, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • H. Ito
    Sokendai, Ibaraki, Japan
  • R. Ito, T. Nagata
    ULVAC, Inc, Chiba, Japan
  • H. Oikawa
    Utsunomiya University, Utsunomiya, Japan
  Funding: The work is supported by JSPS KAKENHI Grant Numbers JP17H04839, JP26600142 and the Collaborative Research Program of ICR Kyoto University (grant 2016-8, 2017-8, 2017-9).
In recent years, it is pointed out that the maximum accelerating gradient of a superconducting RF cavity can be pushed up by coating the inner surface of cavity with a multilayer thin-film structure that consists of alternate insulator and superconductive layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices start penetrate into the first superconductor layer. We made a sample that has NbN/SiO2 thin-film structure on pure Nb substrate by DC magnetron sputtering method. In this paper, we will report the measurement results of effective Hc1 of the sample by the third-harmonic voltage method.
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THPAL156 High-Power Test of a Compact X-Band RF Rotary Joint GUI, linac, network, cathode 4017
  • J. Liu, H.B. Chen, J.Q. Qiu, J. Shi, Z.H. Wang, X.W. Wu, H. Zha
    TUB, Beijing, People's Republic of China
  A compact X-band (9.3 GHz) RF rotary joint has been developed in the accelerator laboratory of Tsinghua University. Cold measurements on the rotary joint using Vector-Network showed good results. In recent high-power tests, the RF rotary joint was operated under a 1.6 MW X-band magnetron. The incident power, the transmitted power and the pulse width of this rotary joint have been measured. The transmitted power kept stable in different rotation angle. In this paper, the setup and results of the high-power tests of this RF rotary joint are presented.  
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THPMK084 E-field Measurement of 9.3 GHz RF cavity for 6 MeV LINAC cavity, linac, electron, hardware 4496
  • D.H. Ha, J.-S. Chai, M. Ghergherehchi, H.S. Kim, J.C. Lee, H. Namgoong, J.H. Seo, Shin, S.W. Shin
    SKKU, Suwon, Republic of Korea
  In order to achieve performance close to the design value, fabricated cavity was tuned at Sunkyunkwan university. Tuning was done in two step: each cell tuning and bead-pull system. Each cell tuning was used to determine the status of each cell and to remove the stop-band. Bead-pull system was used to measure the E-field distribution and obtain the required field flatness. This paper describes each cell measurement data and bead-pull measurement system and data.
x-band, linac, measurement
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THPML091 Design of a High Gradient 60 GHz Dielectric Accelerating Structure experiment, acceleration, electron, simulation 4873
  • D.Z. Cao, D. Dan, W. Gai, C.-X. Tang, H. Zha
    TUB, Beijing, People's Republic of China
  RF breakdown are the main limitation for the application of high gradient structures. Higher frequencies and shorter pulse length benefit the design of accelerating structure for the breakdown threshold of surface field is Es=f1/2 τ-1/4. Power source which generates very short V-band pulse with nearly hundred megawatt is now available. The paper presents the analysis of a V-band dielectric acceleration structure and power source. Future plan about RF transmission and power coupling of the whole structure will be discussed.  
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THPML113 Design and Simulation of the Waveguide Coupler for the Cavity Beam Monitor GUI, cavity, simulation, coupling 4932
  • Q. Wang, Q. Luo, B.G. Sun, F.F. Wu, Y.L. Yang, Z.R. Zhou
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • Y.W. Wu
    USTC, Hefei, Anhui, People's Republic of China
  Funding: Supported by The National Key Research and Development Program of China (2016YFA0401900), NSFC (11375178, 11575181) and the Fundamental Research Funds for the Central Universities (WK2310000046)
The waveguide coupling is an important way to extract the signals of the specific eigenmodes required. The design of the waveguide coupler, including the waveguide-to-coaxial adapter behind it for the cavity bunch length monitor is presented. The influence of the dimension parameters is analyzed, which offers the theoretical support for the design and application of cavity bunch length monitor or cavity beam position monitor (CBPM). A series simulation based on CST is performed to verify the feasibility, and the simulation results show good performance.
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