R&D ON STRIPLINES FOR THE CLIC DR KICKERS

1. R&D ON STRIPLINES FOR THE CLIC DR KICKERS C. Belver-Aguilar (IFIC) Acknowledgements: A. Faus-Golfe (IFIC), F. Toral (CIEMAT), M. Barnes (CERN) ICFA Beam Dynamics Mini WorkshoponLowEmittanceRings 2011 3-5 October 2011 Heraklion, Greece

2. INTRODUCTION The CLIC designreliesonthepresence of PDRs and DRstoachievetheverylowemittanceneeded. Kickers are requiredtoinjectbeaminto and extractbeamfromthe PDR and DR • 8 kicker systems will be needed at CLIC PDR and DRs • damping rings reduce beam emittance; hence kickers must be excellent field homogeneity and very low beam coupling impedance

3. STRIPLINE KICKER OPERATION Lorentzforceoverthechargedparticles of thebeam: for a TEM mode 2 modes of kickeroperation: odd and evenmode

4. Virtual Ground +/-ve +ve -ve STRIPLINE KICKER OPERATION • Striplines driven to same magnitude, but opposite polarity, voltage, to extract beam •  ODD mode characteristic impedance. • Total capacitance (C) is given by: • capacitance between a stripline and virtual ground (C11) • capacitance between a stripline and beam-pipe ground (2C12) • Same polarity and magnitude of current / voltage induced on both striplines by beam. •  EVEN mode characteristic impedance • Capacitance (C) is given by: • capacitance between a stripline and beam-pipe ground (C11) Beam pipe Ground Beam pipe Ground 2C12 2C12 C11 C11 C11 C11 Beam onlyduring 0.01% of a periodthekickerworksout in theoddmode +/-ve T1 T2

5. ODD MODE CHARACTERISTIC IMPEDANCE OPTIMIZATION STRIPLINE CROSS SECTION: defines thecharacteristicimpedance of thestriplines and thehomogeneity of thefield. Twotypes of vacuumchamberhavebeenstudied: CYLINDRICAL and RACETRACK vacuumchamber. easychambertobemanufactured betterfromthebeamimpedancepoint of view Optimizedgeometry in ordertoachieve Z0 = (50 ± 1) Ω and thefieldhomogeneityrequired Z0o = 49.5 Ω

6. FIELD HOMOGENEITY OPTIMIZATION 20 mm • CLIC DR specifications: Field inhomogeneity: • ±0.1 %(1e-3) for DR injection (over 3.5 mm radius); • ±0.01 % (1e-4) for DR extraction (over 1 mm radius). 7 mm STRIPLINE STRIPLINE 2 mm • Sensitivity of field homogeneity to parameter variations from the optimized design • Contour plots of field inhomogeneity in the kicker aperture for the optimized design (courtesy of J. Holma)

7. BEAM IMPEDANCE OPTIMIZATION: FIRST RESULTS BEAM IMPEDANCE: defines theinteraction of thebeamwiththekicker, resulting in beamenergylost and a beamshapeperturbation. L l l Longitudinal beam coupling impedance for untapered (Chao) and tapered stripline kicker (S. Smith, SLAC): How can wedecreasethe longitudinal beamimpedance? Optimizingthekickergeometry in ordertoachieve 50 Ωevenmodecharacteristicimpedance, Thanksto C. Zannini and G. Rumolowhohelped me tolearn CST Particle Studio.

8. CONCLUSIONS • The kicker design for the CLIC DR is presently being studied. By using HFSS simulations the stripline kicker cross section has been optimized in order to obtain the required characteristic impedance and field homogeneity. • 3D models in CST Particle Studio have been used to study the longitudinal beam impedance. Initial predictions, for both untapered and tapered striplines, compare well with analytical equations. • The next step will be optimize the geometry of the kicker in order to obtain50Ω even mode characteristicimpedance, as well as thefieldhomogeneityrequired. In additionitisdesirablethattheoddmodecharacteristicimpedance, duringoperation, is as close as possibleto 50 Ω. • Once the new geometry is found, new longitudinal and transverse beam impedance simulations will be carried out. After that, wakefields calculations will be done. These wakefield results will be used for G. Rumolo (CERN), who will study the beam dynamics effects of the kicker.

9. BIBLIOGRAPHY • Y. Papaphilippou, Parameter Specification, EDMS 989080, Kickers for the CLIC Damping and Pre-damping Rings, PBS reference: 1.2.-.10. • I. Rodríguez, Calculation Methodology and Fabrication Procedures for Particle Accelerator Strip-line Kickers: application to the CTF3 Combiner Ring Extraction Kicker and TL2 Tail Clippers (2009). • D.M. Pozar, Microwave Engineering. Third Edition. • A. Chao and M. Tigner (Editors), Handbook of Accelerator Physics and Engineering 1998. • S. Smith, SLAC, Private communications. • D. Goldberg, G. Lambertson: Dynamic Devices: A primer on Pickups and Kickers, AIP Conf. Proc. No. 249 (1992).