Cavities - Design
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RF Basics and TM Cavities  
  • E. Jensen
    CERN, Meyrin, Switzerland
  Starting from basic principles, the lecture introduces waveguides and cavities, along with the quantities used to describe their performance. Narrowing down to a class of cavities with purely transverse magnetic fields (TM), which in the form of "elliptical cavities" are most frequently used for superconducting RF, guidelines are given how to optimize these cavities for different uses. Finally, some ancillaries (HOM dampers, couplers, tuners) are briefly mentioned.  
slides icon Slides THTU2 [41.246 MB]  
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MOP063 Beam Loading in the BESSY VSR SRF Cavities 217
  • A.V. Tsakanian, H.-W. Glock, J. Knobloch, A.V. Vélez
    HZB, Berlin, Germany
  The BESSY VSR upgrade of the BESSY II light source represents a novel approach to simultaneously store long (ca. 15 ps) and short (ca. 1.7 ps) bunches in the storage ring at currents up to 300 mA. This challenging goal requires installation of four new 4-cell SRF cavities (2x1.5 GHz and 2x1.75 GHz) in one module for installation in a single straight. As far as we are aware of, this is the first installation of multi-cell L-Band cavities in a high-current storage ring. These cavities are equipped with newly developed waveguide HOM dampers necessary for stable operation. Up to 2 kW of HOM power must be absorbed. Operating two SRF cavities for each frequency will also enable transparent parking of the cavities for the beam. Based on wakefield theory, a technique for beam loading calculation will be presented. The expected beam loading both at 2 K and at room temperature has been analyzed to evaluate transparent parking for both situations. The presented study is performed for various BESSY II and VSR bunch filling patterns with 300 mA beam current.  
DOI • reference for this paper ※  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP064 Performance of First Prototype Multi-Cell Low-Surface-Field Shape Cavity 222
  • R.L. Geng
    JLab, Newport News, Virginia, USA
  • Y. Fuwa, Y. Iwashita
    Kyoto ICR, Uji, Kyoto, Japan
  • H. Hayano
    KEK, Ibaraki, Japan
  • H. Ito
    Sokendai, Ibaraki, Japan
  • Z. Li
    SLAC, Menlo Park, California, USA
  The idea of cavity shaping for higher ultimate acceleration gradients has been proposed for some time, Low Loss/Ichiro and Re-entrant being examples, both seeking a lower Hpk/Eacc at the expense of a higher Epk/Eacc. While experimental verification in single-cell cavities of those shapes was very successful including the record gradient of 59 MV/m, pushing multi-cell cavities of those shapes to higher gradients was prevented by field emission. The Low-Surface-Field (LSF) shape seeks not only a lower Hpk/Eacc but also a lower Epk/Eacc, therefore it has the advantage of raising ultimate gradient at reduced field emission. The first multi-cell LSF shape prototype cavity was built using the standard forming and welding techniques. RF tests have been carried out, following standard ILC TDR baseline surface processing and treatment recipe. Three out of five cells achieved Hpk values corresponding to Eacc 50 MV/m. The current limit is the field emission in end cells. Instrumented testing following end-cell wiping and HPR with larger nozzles is in progress. We will present detailed experimental results and preparation procedures.  
DOI • reference for this paper ※  
About • paper received ※ 24 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP065 Upgrade of the S-DALINAC Injector Capture Section 227
  • S. Weih, M. Arnold, J. Enders, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
  • D.B. Bazyl, H. De Gersem, W.F.O. Müller
    TEMF, TU Darmstadt, Darmstadt, Germany
  Funding: Work supported by DFG through GRK 2128 "AccelencE"
The superconducting injector section of the S-DALINAC (superconducting Darmstadt linear electron accelerator) [1] constists of two cryomodules with three 3-GHz SRF cavities in total. The first cavity of this pre-accelerator is currently a 5-cell structure designed for relativistic particle velocities. Since the gun delivers a 250 keV beam (β=0.74), this cavity is not suited for an efficient capture of the low-energy electron bunches provided by the normal-conducting section of the injector. Beam dynamics simulations and operational experience have shown a large low-energy tail in the phase-space distribution of the bunch downstream of the injector, which arises from the large phase-slippage during the capture in the 5-cell. It is therefore intended to replace the cavity with a beta-adapted 6-cell, re-using most of the cryostat parts. This contribution presents the status of the injector upgrade and the layout and manufacturing status of the new cavity.
*N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018)
DOI • reference for this paper ※  
About • paper received ※ 21 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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MOP070 Investigation of the Critical RF Fields of Superconducting Cavity Connections 230
SUSP026   use link to see paper's listing under its alternate paper code  
  • J.C. Wolff, J.I. Iversen, D. Klinke, D. Kostin, D. Reschke, S. Sievers, A. Sulimov, J.H. Thie, M. Wiencek
    DESY, Hamburg, Germany
  • R. Wendel, J.C. Wolff
    HAW Hamburg, Hamburg, Germany
  To optimise the length of the drift tube of a superconducting cavity (SC), it is required to know the critical value of the RF fields to prevent a potential early quench at the flange connection in case of a drift tube length reduction. To avoid changes on the SC which has been used for the tests, all RF cryogenic experiments have been carried out by using a cylinder in the center of a 1-cell cavity drift tube to increase the field magnitude at the connection. This cylinder has been designed and optimised by RF simulations to provide a field density at the connection twice as high as at a chosen reference point near the iris. Hence also a test SC with a comparatively low gradient can be used without causing field restrictions. In this contribution an approach to investigate the field limitations of 1.3 GHz TESLA-Shape SC connections and thereby the minimal drift tube length based on simulations will be presented.  
DOI • reference for this paper ※  
About • paper received ※ 23 June 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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