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HOM Studies for TESLA (and some ideas for SPL)

HOM Studies for TESLA (and some ideas for SPL). Hans-Walter Glock Institut für Allgemeine Elektrotechnik, Universität Rostock CERN, SPL-Meeting 11./12.12.08. Accelerator Group at AET, Uni Rostock. Prof. Dr. Ursula van Rienen Dr. Gisela Pöplau Dr. Hans-Walter Glock Dr. Dirk Hecht

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HOM Studies for TESLA (and some ideas for SPL)

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  1. HOM Studies for TESLA(and some ideas for SPL) Hans-Walter Glock Institut für Allgemeine Elektrotechnik, Universität Rostock CERN, SPL-Meeting 11./12.12.08

  2. Accelerator Group at AET, Uni Rostock • Prof. Dr. Ursula van Rienen • Dr. Gisela Pöplau • Dr. Hans-Walter Glock • Dr. Dirk Hecht • Dipl.-Ing. MSc. Aleksandar Markovik • Dipl.-Math. Christian Bahls H.-W. Glock

  3. Accelerator Group at AET, Uni Rostock • = • 3 mathematicians, 2 with long term accelerator experience • + • 2 physicists, both working theoretically and experimentally • + • 1 engineer, combined accelerator and software competence H.-W. Glock

  4. Some time stamps of (incomplete) TESLA HOM history • < 91: various HOM-coupler designs (CERN, DESY, ...) • 94: HOM coupler design + position fixed (Tesla Reps. 94-7, 94-16, Sekutowicz, Proch) • 98: "trapped" modes analysis (Marhauser, PhD, Frankfurt) • 98: Superstructure 4x7, entire recalculation (Tesla Rep. 98-8, Sekutowicz) • 98: Absorber design (Jöstingmeier, Dohlus) • 99: 2.585-GHz-Mode at TTF (Baboi, Napoly, ... EPAC 00) • 01: Proposal of mirroring one HOM coupler (Dohlus) • 04 .. now: HOM signal for BPM (Baboi, Eddy, ...) H.-W. Glock

  5. A few tools developed in the TESLA framework • Discretization • Field dynamics in large structures • Coupling calculations based on multidimensional scattering properties (CSC) H.-W. Glock

  6. Shape-adopted 2D-grid (MAFIA) • Mesh line crossings exactly at cavity shape: • important for tuning/field flatness calculations • Automatic mesh construction ... up to 36 cells H.-W. Glock

  7. Ez /(V/m) t = T 2500 9 l / 2 3 l / 2 2000 1500 1000 500 z/m 0 0 1 2 3 4 Ez /(kV/m) Structure of CDR „Superstructure“, J. Sekutowicz 1997 t = 1000 T 300 200 100 0 -100 -200 z/m -300 3 0 1 2 4 Ez /(MV/m) t = 106 T 40 20 0 -20 -40 z/m 0 1 2 3 4 Filling of TESLA “Superstructure“- Semi-analytical calculation l / 2 7 l / 2 rf period T = 0.7688517112 ns H.-W. Glock; D. Hecht; U. van Rienen; M. Dohlus. Filling and Beam Loading in TESLA Superstructures. Proc. of the 6th European Particle Accelerator Conference EPAC98, (1998): 1248-1250. H.-W. Glock

  8. CSC - 9-Cell Resonator with Couplers Input coupler HOM coupler CAD-plot: DESY HOM coupler • Resonator without couplers: N ~ 29,000 (2D) • N ~ 12·106 (3D) • Resonator with couplers: N ~ 15·106 (3D) •  N increases by ~ 500 • CSC: „Coupled S-Parameter Calculation“ allows for combination of 2D- and 3D-simulations K. Rothemund; H.-W. Glock; U. van Rienen. Eigenmode Calculation of Complex RF-Structures using S-Parameters. IEEE Transactions on Magnetics, Vol. 36, (2000): 1501-1503. H.-W. Glock

  9. Coupler 3D-calculation: MAFIA or CST-Studio • Determine scattering properties regarding • sufficient number of modes in beam pipe ports • coaxial ports • as input for coupling calculations H.-W. Glock

  10. Identical sections SHom1Hom2 /dB Weak dependence on position CSC - Resonator Chain – Variation of Tube Length HOM1 HOM2 Variation of coupler position 1,000 frequency points 31 lengths resulting S-matrix: 16 x 16 intern 84 x 84, 1h 12min, Pentium III, 1 GHz H.-W. Glock

  11. Demonstration of high-Q-modes in HOM-damped cavity • Significant Q reduction due to mirrored HOM coupler H.-W. Glock

  12. A few ideas according SPL, inspired by TESLA • Different wakefield regimes • Coupler vs. Absorbers • NC measurement cavity model H.-W. Glock

  13. Different wakefield regimes • localized in single resonator, well coupled to neighbouring coupler • localized in inner cells ("trapped"), poorly coupled • coupling between (strings of) neighbouring resonators • propagating though beam pipe ... need adopted methods for counteraction and calculation H.-W. Glock

  14. Coupler vs. absorber? • + absorber: easier construction, insensitive to polarizations • - absorber: power deposition "inside" structure, needs "warm(er)" section => access to "inner" fields may be difficult (if shared for more than single cav.), vacuum • + coupler: external power dissipation, attachs every cavity, allows for signal monitoring • - coupler: more complicated, cooling, multipacting may be a problem H.-W. Glock

  15. NC measurement cavity model ? • +: • cheap (but by far not for free) • easy to perform field profile measurements (bead pull), no clean room • easy modification, e.g. additional coupling holes • no sc infrastructure needed for experiments • -: • poor Q (~10^4) => poor mode separation, damping due to weakly coupled couplers/absorbers difficult (impossible) to measure • coupling through a resonator may have much larger bandwidth than in sc case • It is not the same. H.-W. Glock

  16. Outlook • Very recent application to BMBF (German Federal Research Ministry) together with CERN: SPL HOM damping measures (start hopefully 1.7.09) • Approved project within EuCard framework together with DESY, Cockroft Institute: HOM signals for BPM (start 1.4.09) Thank you! H.-W. Glock

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