Status of CTC activities for the Damping rings CLIC Technical Committee Status of CTC activities for the Damping rings Yannis PAPAPHILIPPOU February 23rd, 2010

DR parameters and challenges High-bunch density Emittance dominated by Intrabeam Scattering, driving energy, lattice, wiggler technology choice and alignment tolerances Electron cloud in e+ ring imposes chamber coatings and efficient photon absorption Fast Ion Instability in the e- ring necessitates low vacuum pressure Space charge sets energy, circumference limits Repetition rate and bunch structure Fast damping achieved with wigglers RF frequency reduction considered due to many challenges @ 2GHz (power source, high peak and average current) Output emittance stability Tight jitter tolerance driving kicker technology Positron beam dimensions from source Pre-damping ring challenges (energy acceptance, dynamic aperture) solved with lattice design Target Parameters NLC CLIC bunch population (109) 7.5 4.1 bunch spacing [ns] 1.4 0.5 number of bunches/train 192 312 number of trains 3 1 Repetition rate [Hz] 120 50 Ext. hor. norm. emittance [nm] 2370 <500 Ext. ver. norm. emittance [nm] <30 <5 Ext. long. norm. emittance [keV.m] 10.9 <4 Inj. hor. norm. emittance [μm] 150 63 Inj. ver. norm. emittance [μm] 1.5 Inj. long. norm. emittance [keV.m] 13.18 1240 Design Parameters CLIC Energy [GeV] 2.86 Circumference [m] 493.2 Energy loss/turn [Me] 5.8 RF voltage [MV] 7.4 Compaction factor 6e-5 Damping time x / s [ms] 1.6 / 0.8 Number of arc cells / wigglers 100/76 Dipole/ wiggler field [T] 1.4/2.5

Wiggler prototypes Two wiggler prototypes 2.5T, 5cm period, built and currently tested by BINP 2.8T, 4cm period, designed by CERN/Un. Karlsruhe BINP prototype did not reach target performance (new prototype) CERN prototype (NbTi @ 40mm period) reached field performance target (either @ 1.9K or extrapolated @ 50mm) On-going work on Nb3Sn mock-up Nb3Sn SC wiggler NbTi SC BINP PM 50 mm period 40 mm period Parameters BINP CERN Bpeak [T] 2.5 2.8 λW [mm] 50 40 Beam aperture full gap [mm] 13 Conductor type NbTi Nb3Sn Operating temperature [K] 4.2

Radiation absorption scheme K. Zolotarev, CLIC09 A 4-wigglers scheme Gap of 13mm (10W/m) Combination of collimators and absorbers Terminal absorber at the end of the straight section (10kW) Mechanical design and impedance estimation for CDR Implication with cryogenics 4

Coatings for e- Cloud Mitigation M. Taborelli LER2010 Amorphous carbon coating showed reduction of e-cloud activity in CESRTA (better than any other coating) Continue coating characterization with additional chambers Understand photo-emission yield and pressure curves (work also in the SPS) Identify collaborations in light source community for chamber tests (SOLEIL, ALBA) bare Al CESRTA e+ TiN TiN new a-C CERN

RF system RF frequency of 2GHz R&D needed for power source High peak and average power of 6.6 and 0.6MW Strong beam loading transient effects Beam power of 6.6MW during 156 ns, no beam during other 1488 ns Small stored energy at 2 GHz Wake-fields and HOM damping should be considered 1GHz frequency being evaluated (2 trains with 1ns bunch spacing) Easier extrapolation from existing designs (e.g. NLC) Lowering peak current and thus transient beam loading Delay line for train recombination A. Grudiev, CLIC08 CLIC DR parameters Circumference [m] 493.2 Energy [GeV] 2.86 Momentum compaction 0.6x10-4 Energy loss per turn[MeV] 5.9 Maximum RF voltage [MV] 7.4 RF frequency [GHz] 2.0 Decision on RF frequency by end of March 2010 Conceptual design including HOM damping to be done for CDR (external collaboration)

Kicker stability M. Barnes CLIC09 Kicker jitter translated in beam jitter in IP, withσjit ≤0.1σx Tolerance typically ~10-4 Double kicker system relaxes requirement, i.e. ~3.3 reduction achieved @ATF Striplines required for achieving low longitudinal coupling impedance Significant R&D needed for PFL (or alternative), switch, transmission cable, feedthroughs, stripline, terminator (PhD thesis student at CERN) Should profit from collaboration with ILC and light source community Y.P., 03/02/2010 ACE 2010