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Status of Wakefield Monitors developments for CLIC accelerating structures 25 Sept. 2009 Franck Peauger, Riccardo Zennaro Alexandre Samoshkin F. Peauger CLIC meeting / 25 Sept. 2009 1 Outline • • • • Context and requirements Time domain simulations of wakefields in AS Design of WFM RF transition Integration in the Two-Beam Test Stand • 180° Hybrid coupler • Test set-up in CTF3 F. Peauger CLIC meeting / 25 Sept. 2009 2 Context Wakefield Monitors are Beam Position Monitors integrated to the drive beam Accelerating Structures (AS) It allows beam-based alignment of AS to remove wakefield effects and emittance growth Emittance growth is very well improved by aligning the AS to an RMS accuracy of 5 µm to the beam F. Peauger CLIC meeting / 25 Sept. 2009 3 Context Electron bunch AS with WFM Girder Girder Movers D. Schulte Wakefield kicks from misaligned AS can be cancelled by another AS One WFM per structure and mean offset of the 8 AS computed F. Peauger CLIC meeting / 25 Sept. 2009 4 WFM dev. plan & requirements Step 1 (2009 - 2010): build one WFM prototype and integrate it into a CERN structure and test on TBTS with CALIFES probe beam Step 2 (2010 - 2011): build 2 or 3 structures fully instrumented and test on TBTS + CALIFES Parameters 8 CLIC Operation 9 CTF3 (CALIFES+TBTS) 9 Charges per bunch 3.7 x 10 3.7 x 10 0.6 nC = 3.75 x 10 Number of bunches 1 - 312 312 1 – 32 - 226 Bunch length 45 – 70 µm 45 – 70 µm 500 µm / 1.66 ps Train length 156 ns max 156 ns 150 ns max Bunch Spacing 0.5 ns 0.5 ns 0.66 ns Accuracy 5 µm 5 µm To be measured Resolution 5 µm < 5 µm To be measured Stability 5 µm To be measured Range ± 2 mm ± 100 µm ± 2 mm Bandwidth 35 MHz 35 MHz TBD Beam Aperture ~ 5.5 mm ~ 5.5 mm ~ 5.5 mm Available length - - - No No No 142812 142812 2/3 Yes Yes N.A. No No N.A. Intercepting device Quantity Used in RT Feedback F. Peauger CLIC Commissioning Machine protection Item CLIC meeting / 25 Sept. 2009 5 WFM additionnal requirements Since there is no place available in the linac, the damping waveguides of the middle cell are used to measure the beam position inside the structure we cannot define the geometry, frequency mode, Q factor … as we do for BPM the WFM works necessarily with strong damped modes (Q ~ 10) !! The WFM design consists in studying the HOM modes and their sensitivity to a beam offset, choosing an operating mode, designing an RF transition to couple this mode and processing the signal We must attenuate the 12 GHz high power accelerating signal to -150 dB !! The RF transition must not reflect any signal to the cell (typically -20 dB from 10 to 35 GHz) The middle cell equipped with the WFM must keep its strong damping functionality (SiC loads) The WFM must be cheap, easy to integrate mechanically in the Two Beam Module and avoid if possible any major additional machining of the cell F. Peauger CLIC meeting / 25 Sept. 2009 6 Wakefield simulation with beam offset GDFIDL Simulations: • Five cells meshed (no symmetry) with a mesh step of 0.1 mm • volume limited to +/- 15 mm in the X and Y directions • PML set at the waveguide extremities (Xmin, Xmax, Ymin, Ymax, Zmin, Zmax) • Beam: 1 bunch of 0.6 nC, σz=3 mm with offset • Simulation stopped at 6.66 ns. • Rectangular ports at the end of the damped waveguides of the middle cell. The two first modes are selected in GdfidL : 1st port mode: Fc = 13.3 GHz E field F. Peauger TM like mode for the beam 2st port mode: Fc = 21.4 GHz E field ydamphaut xdamphaut xdampbas ydampbas • Total of 90e6 meshs • Time computation of 9 to 13 hours with 36 hosts on LXCLIC cluster / 25 Sept. 2009 TE like modeCLIC for meeting the beam 7 TM like modes with beam offset of 1 mm Port signal amplitude (voltage) Y+ X- & X+ Beam dx=1mm offset X+ X- Y+ & Y- Time (s) YPort signal amplitude (voltage) Port signal amplitude (voltage) 11.94 GHz 18 GHz = First dipole-band mode F. Peauger CLIC meeting / 25 Sept. 2009 F (Hz) 8 Time (s) monopole / dipole mode configuration Monopole mode Dipole mode E Field E Field Opposite ports signals are in phase Opposite ports signal have opposite phase When we substract the opposite port signals, the monopole mode is cancelled and the dipole mode amplitude is increased F. Peauger CLIC meeting / 25 Sept. 2009 9 TM modes after 180° perfect recombination Y+ X- Recombined port signal amplitude (voltage) Beam dx=1mm offset DX=X+-X- X+ DY=Y+-YY- Time (s) Recombined port signal amplitude 14.81 GHz Recombined port signal amplitude (voltage) 18.19 GHz 11.95 GHz F (GHz) F. Peauger CLIC meeting / 25 Sept. 2009 Time (s) 10 Variation of beam offset amplitude Recombined port signal amplitude DX (voltage) dx = 1 mm dx = 0.8 mm dx = 0.6 mm dx = -1 mm Time (s) F. Peauger CLIC meeting / 25 Sept. 2009 11 Linearity Max. amplitude of the delta signal (voltage) 40 30 20 y = 33.092x + 0.1028 10 0 -1.5 -1 -0.5 0 0.5 1 1.5 Offset dx (mm) -10 -20 -30 -40 The 18.2 GHz mode works quite well as a cavity BPM mode ! But we need to design an RF transition that couple this mode, attenuate 12 GHz mode, avoid reflection, allows strond damping, etc… F. Peauger CLIC meeting / 25 Sept. 2009 12 RF transition design Long waveguide with cut-off above 12 GHz + 90° E-bend Coax coupler designed to have -10 dB transmission 55 mm Load location 15 mm F. Peauger CLIC meeting / 25 Sept. 2009 13 Geometry of WFM RF transition Damped waveguide Antenna Coaxial waveguide (K type) 1 2 p R1 R2 L2 Load d a Cell L1 Cell axis F. Peauger CLIC meeting / 25 Sept. 2009 b P 1 mm 1 2.92 mm 2 1.27 mm a 11.25 mm b 7.011 mm d 5.625 mm R1 0.2 mm R2 >15 mm L1 70 mm L2 18 mm 14 RF transition transfer function T(f) T (f) (S parameters) -11 dB 3 2 S11 S13 -145 dB 1 S12 12 GHz F. Peauger 18 GHz CLIC meeting / 25 Sept. 2009 15 TM modes after RF Transition and 180° perfect recombination with dx=1mm beam offset Recombined port signal amplitude (voltage) Y+ U0 X- U1 DX=X+-XX+ DY=Y+-Y- YTime (s) Recombined port signal amplitude U1 f T ( f ) U 0 ( f ) 18.14 GHz 13.88 GHz Given by HFSS ~ 1 – 3 GHz band pass CLIC meeting / 25 Sept. 2009 filter around 18.1 GHz16 F (GHz) F. Peauger Given by Gdfidl Resolution The power and voltage are linked by: P U2 Dipole mode 18 GHz: Simulation results (at the coax pick-up, after the RF transition) dx=1mm, q=0.6nC → U1 ≈ 1 V Extrapolation for the commissioning case (voltage varies linearly with offset and charge) dx=5µm, q=0.06nC, (s=70µm) → U1 = 500 µV → U1 = 5 mV Extrapolation for the nominal case dx=5µm, q=0.6nC, (s=60µm) Accelerating mode 12 GHz: •For 60 MW input power, there is 3 nW at the coax pick-up, after the RF transition → equivalent to UHP = 56 µV + Thermal noise and noise from signal processing to be evaluated F. Peauger CLIC meeting / 25 Sept. 2009 17 Integration in the Two Beam Test Stand - Design a support and ensure good electrical contact between the WFM and the structure - Must make a hole in U support for the “Y- waveguide” F. Peauger CLIC meeting / 25 Sept. 2009 18 Integration in the Two Beam Test Stand Or We would like to reserve one available flange (150 mm diameter) for a special CF flange with four feedthroughs F. Peauger CLIC meeting / 25 Sept. 2009 19 180° Hybrid coupler Hybrid couplers are the special case of a four-port directional coupler that is designed for a 3dB (equal) power split and a 180 degree phase shift between two output ports Ring Hybrid Junction Tapered Coupled Line Hybrid Magic Tees When using as a combiner, input signals are applied at port 2 and 3, the sum of the inputs will be formed at port 1 while the difference at port 4. In theory: S12 = S13 = -3dB and S11 = S14 = -40 dB F. Peauger CLIC meeting / 25 Sept. 2009 20 180° Hybrid coupler • Two tapered-line directional couplers cascaded • Excellent phase and amplitude matching • Realized with a three-layer stripline configuration • Etched on opposite sides of a thin coupler circuit board, sandwiched between a pair of equal thickness Duroid boards F. Peauger CLIC meeting / 25 Sept. 2009 21 Layout of WFM prototype test with Hybrid : WFM – transition, qty 4, output connector = K female, UHV compatible : semi rigide cable, Type?, qty 4, length ≈ 400 mm , input connector = K male, output connector = K female, UHV compatible : CF flange feedthrough, qty 1, 4 connectors, input connector = K male (vacuum side), output connector = K female, UHV compatible : Flexible cable, qty 4, length ≈ 30 m , input connector = K male, output connector = K female, : 180° Hybrid coupler, input connector = K male, output connector = K female TBTS rack Scope Diode detector Bandpass filter ≈ 30 m Klystron gallery Front Back Accelerating structure TBTS Accelerating structure tank F. Peauger CLIC meeting / 25 Sept. 2009 CLEX – beam tunnel 22 Conclusion (1/2) • The WFM Context, specifications and development program well defined with the objective to demonstrate the WFM concept before end of 2010 • We have developed a methodology to run Gdfidl from CEA Saclay on the CERN Cluster, and couple the results to HFSS simulations • The TM like mode at 18.2 GHz has been identified and well studied in time domain. It will be used as classical cavity BPM dipole mode with 180° recombination • We proposed a simple design of the WFM RF transition which should meet the long list of requirements • We would like to investigate TE like modes around 23 GHz. Additional simulations are required • But we also would like to freeze the design of the WFM prototype soon in order to start the mechanical study and procurement of components • We should not forget to work on the electronic for signal processing F. Peauger CLIC meeting / 25 Sept. 2009 23 Conclusion (2/2) • Important topic for CLIC • Very interesting R&D program • Good continuation after CALIFES for CEA Saclay Thank you for your attention F. Peauger CLIC meeting / 25 Sept. 2009 24 Extra - slides F. Peauger CLIC meeting / 25 Sept. 2009 25 Wakefield simulation with one symetry GDFIDL Simulations: •Five cells meshed with one symetry (half of the structure is meshed) • Perfect magnetic boundary condition on XZ plane • mesh step of 0.05 mm • PML set at the waveguide extremities (Xmin, Xmax, Ymax, Zmin, Zmax) • Beam: 1 bunch of 0.6 nC, σz=1 mm, offset Δx = 1 mm • Simulation stopped at 6.66 ns. • Rectangular ports at the end of the damped waveguides of the middle cell. The first modes is selected in GdfidL so that longitudinal (TM) modes can be recorded F. Peauger Total of 156.8e6 meshs 14 hours with 36 hosts machines lxclic CLIC meeting / 25 Sept. 2009 26 TM modes responses Y+ Beam 1mm offset X- X+ 11.83 GHz 15.15 GHz F. Peauger CLIC meeting / 25 Sept. 2009 27 TM modes after 180° perfect recombination Y+ X- X+ DX=X+-X- 11.98 GHz 15.19 GHz 18.47 GHz F. Peauger CLIC meeting / 25 Sept. 2009 28 RF cable under vacuum F. Peauger CLIC meeting / 25 Sept. 2009 29 CF Flange feedthroughs CF Flange: Dext152mm x2 Flange Size=2.75"CF Number of feedthrough = 4 Grounded 50-Ohm Ref. = IFDCG042013 F. Peauger CLIC meeting / 25 Sept. 2009 Dimensions (inches) A=0.63 B= 0.92 C=2.75 (69.85mm) D= 1.38 E=0.87 30 Two Beam Module integration Vac. Manifold: 30 x 30 mmm² F. Peauger CLIC meeting / 25 Sept. 2009 31