Kicker and RF systems for Damping Rings CLIC Technical Committee Kicker and RF systems for Damping Rings F. Antoniou, M. Barnes, T. Fowler, A. Grudiev, Y. Papaphilippou February3rd, 2009

Design optimisation for CDR (2010) M. Korostelev, PhD thesis, 2006 Outline CLIC damping rings (DR) layout and parameters DR injection and extraction optics DR septa and kicker parameters DR RF system specifications Pre-damping rings (PDR) parameters Kicker and RD considerations for PDR Summary CLIC parameter note 2005 CLIC parameter note 2008 Design optimisation for CDR (2010) M. Korostelev, PhD thesis, 2006 03/02/09 CTC, YP

CLIC damping ring layout 03/02/09 M. Korostelev, PhD thesis, EPFL 2006

DR bunch structure and timing CLIC DR timing parameters Old (2005) New (2008) Repetition rate [Hz] 150 50 Number of bunches 110 312 Number of trains 4 1 Bunch spacing [ns] 0.533 0.500 Revolution Time [μs] 1.2 >1.2 Machine pulse [ms] 6.67 20 H/V/L damping times [ms] 2.8/2.8/1.4 1.5/1.5/0.76 Reduction of repetition rate from 150 to 50Hz leaves enough time for the emittances to reach their equilibrium Bunch spacing increased almost to same level as for the interleaved train scheme Interleaved train scheme abandoned Extraction kicker rise time relaxed Injection and extraction process simplified 312 bunches with 0.5ns spacing, fill 13% of the rings 4

DR injection/extraction optics Injection and extraction system placed at the same area, upstream of the super-conducting wigglers Kickers placed at maximum beta functions for minimum deflection angle Septa and kickers share the same cell Additional cells to be added in order to increase available space for elements and protection system Phase advance between injection (extraction) septa and kickers of around π/2 M. Korostelev, PhD thesis, EPFL 2006 03/02/09 CTC, YP

DR Septa parameters DR septa parameters SEP-1 SEP-2 Effective length [m] 0.4 0.5 Bending angle [mrad] 13 42 Field integral [T.m] 0.11 0.34 Blade thickness [mm] 5 Same parameters for injection/extraction elements due to optics mirror symmetry Septum parameters are scaled from NLC damping rings Two DC modules with blade thickness of 5 and 13mm Effective length can be increased to 2m if additional cells are added Larger septa blade thicknesses and smaller peak field 03/02/09 CTC, YP

DR Kicker parameters Rise and fall time significantly increased Effective length can be increased to 2m Smaller peak field Kicker stability refers to field uniformity and pulse-to-pulse stability Tolerance of 0.1σx beam centroid jitter DR kicker parameters Old New Rise and fall time [ns] 25 1000 Flat top [ns] 142 ~160 Repetition rate [Hz] 150 50 Effective length [m] 0.4 0.4-2 Aperture [mm] 20 Kick [mrad] 2.45 3 Field [Gauss] 500 <610 Kicker stability 1.4x10-3 @ inj 1.5x10-4 @ ext Second kicker in transfer line @ phase advance of π for jitter compensation (as in NLC/ATF) Achieved 2.8x10-4 at ATF for shorter rise/fall times and flat top Third kicker, delay line and RF deflector are removed Contribution to beam impedance should be addressed (budget of a few MΩ/m in transverse and a few Ω in longitudinal) –external circuit may be important

DR RF system RF frequency of 2GHz A. Grudiev CLIC DR parameters Circumference [m] 365.2 Energy [GeV] 2.42 Momentum compaction 0.8x10-4 Energy loss per turn[MeV] 3.9 Maximum RF voltage [MV] 4.115 RF frequency [GHz] 2.0 RF frequency of 2GHz Power source is an R&D item at this frequency High peak and average power of 5 and 0.7MW Strong beam loading transient effects Beam power of ~5 MW during 156 ns, no beam during other 1060 ns Small stored energy at 2 GHz Wake-fields and HOM damping should be considered High energy loss per turn at relatively low voltage results in large φs of 72o (see also LEP) Bucket becomes non-linear Small energy acceptance of 0.8% RF voltage increased to 5MV (energy acceptance of 2.6%) As longitudinal emittance is decreased (3.5 keV.m), horizontal emittance increased to 470nm 03/02/09 CTC, YP

PDR working parameters F. Antoniou Parameter [unit] Value beam energy [GeV] circumference [m] bunch population [E+09] bunch spacing [ns] bunches per train rms bunch length [mm] rms momentum spread [%] hor. Emittance w/o IBS [nm] no. of arc bends arc-dipole field [T] length of arc dipole [m] number of wigglers wiggler field [T] length of wiggler [m] wiggler period [cm] mom. compaction [10-5] RF frequency [GHz] energy loss/turn [MeV] RF voltage [MV] h/v/l damping times [ms] Revolution time [ns] Repetition rate [Hz] 2.424 260.1 4.5 0.5 312 0.2 0.3 13000 30 1.7 1 20 2 4.7 1.54 16 2.7/2.7/1.35 870 50 312 bunches with 0.5ns spacing, fill 18% of the pre-damping rings Designed for large momentum acceptance and fast damping Large RF voltage, small momentum compaction factor Injected Parameters e- e+ Bunch population [109] 4.4 6.4 Bunch length [mm] 1 5 Energy Spread [%] 0.1 2.7 Hor.,Ver Norm. emittance [nm] 100 x 103 9.3 x 106 PDR Extracted specs Value Bunch length [mm] 10 Energy Spread [%] 0.5 Hor. Norm. emittance [nm] 63000 Ver. Norm. emittance [nm] 1500 9

PDR injection/extraction optics Kickers Septa PDR kicker parameters Value Rise and fall time [ns] 700 Flat top [ns] ~160 Repetition rate [Hz] 50 Effective length [m] 2 Aperture [mm] 20 Kick [mrad] Field [Gauss] 150 Kicker stability 1.8x10-2 @ inj 1.4x10-3 @ ext Injection and extraction system placed at symmetric points of the matching area, upstream of the super-conducting wigglers Kickers placed at maximum beta functions with available space of around 2m Phase advance between septa and kickers of around π/2 Kicker stability at extraction as DR injection 03/02/09 CTC, YP

PDR RF system RF frequency of 2GHz Power source is an R&D item at this frequency Peak and average power of 2.1 and 0.4MW Transient beam loading effects Beam power of ~2MW during 156 ns, no beam during other 710 ns Wake-fields and HOM damping should be considered Peak and average current of 1.4 and 0.24A High RF voltage of 16MV in order to assure large momentum acceptance of 21% Especially for longitudinal stacking of polarized positrons CLIC PDR parameters Circumference [m] 260.1 Energy [GeV] 2.42 Momentum compaction 0.5x10-4 Energy loss per turn[MeV] 1.5 Maximum RF voltage [MV] 16 RF frequency [GHz] 2.0 Space reserved in the FODO straight section upstream of the wigglers and the matching section Geometrical acceptance of around 40mm 03/02/09 CTC, YP

Summary DR injection and extraction systems DR RF system Extraction process simplified (1 train) Main issues the kicker stability DR RF system RF voltage increased for larger energy acceptance Main issue the RF frequency (power source) and transient beam loading PDR kickers are more conventional PDR RF system RF frequency of 2GHz is the main issue Large RF voltage needed (space) Design should target for low impedance and general impact to collective effects (HOM damping) should be addressed 03/02/09 CTC, YP