with contributions from CLIC e+ sources L. Rinolfi with contributions from E. Bulyak, F. Zimmermann Tanks to H. Braun, R. Chehab, P. Gladkikh, T. Kamitani, M. Kuriki, A. Latina, T. Omori, J. Sheppard, D. Schulte, J. Urakawa, A. Variola

Short history of CLIC e+ source 1997, CLIC conventional unpolarized source (L. Rinolfi) => CLIC Note 354 2000, CLIC undulator source (T. Kamitani) 2001, CLIC detailed e+ study: target, capture, pre-linac (T. Kamitani, L. Rinolfi) => CLIC Note 465 2001, Snowmass meeting (R. Assmann, F. Zimmermann) => JLC Compton scheme preferred option CLIC Note 501 2005, new ILC Compton scheme (F. Zimmermann) => CLIC Note 639 2006 April, POSIPOL 2006 workshop (Collaboration CERN/KEK/LAL/KIPT) => Laser Compton study for CLIC 2006 June, EPAC Conference => CLIC Note 674 CERN; 1)NSC/KIPT,Kharkov; 2)KEK; 3)DESY, Zeuthen; 4)LAL, Orsay; 5)IPN, Lyon; 6)BINP, Novosibirsk ; 7) IHEP, Beijing; 8) INFN Frascati; 9)LPI, Moscow; 10)NIRS, Chiba, Japan; 11) Waseda University, Japan; 12) Hiroshima University; 13)Sumitomo Heavy Indust. Ltd., Tokyo 2007, Major CLIC parameters changes (CLIC Study group)

Major CLIC parameters changes In January 2007, new CLIC key parameters have been adopted: Accelerating gradient: 150 MV/m => 100 MV/m RF frequency: 30 GHz => 12 GHz => All CLIC study is today under revision, in particular the CLIC Injector complex and the e+ production (polarized and unpolarized).

Possible CLIC methods for e+ production The basic three: conventional undulator-based laser Compton based Two other methods: head-on collision using the CLIC Drive Beam ERL

The CLIC Injector complex in 2007 Base line configuration e+ Main Linac e- Main Linac e- BC2 e+ BC2 12 GHz 2.3 GV 12 GHz 2.3 GV 12 GHz, 100 MV/m, 21 km 12 GHz, 100 MV/m, 21 km 9 GeV 48 km maximum 3 TeV Base line configuration Booster Linac 6.6 GeV 3 GHz  360 m e+ BC1 e- BC1  10 m  10 m 3 GHz 162 MV 3 GHz 162 MV 2.424 GeV 360 m e+ DR 2.424 GeV 360 m e- DR e+ PDR e- PDR 2.424 GeV 2.424 GeV Injector Linac 2.2 GeV 1.5 GHz  150 m e-/e+ Target Laser Primary beam Linac for e- 2 GeV Pre-injector Linac for e+ 200 MeV Pre-injector Linac for e- 200 MeV Laser DC gun Polarized e- RF gun Unpolarized e- 1.5 GHz 1.5 GHz 1.5 GHz  150 m  15 m  15 m

Main beam parameters comparison At the entrance of the Main Linac for e- and e+ NLC (1 TeV) CLIC 2007 (3 TeV) ILC (Nominal) Energy E GeV 8 9 15 Bunch population N 109 7.5 4 - 4.1 20 Nb bunches / train nb - 190 311 2625 Bunch spacing Dtb ns 1.4 0.667 (8 RF periods) 369 Train length tpulse 266 207 968625 Emittances gex , gey nm, nm.rad 3300, 30 600, 10 8400, 24 rms bunch length sz mm 90-140 43 - 45 300 rms energy spread sE % 0.68 (3.2 % FW) 1.5 - 2 1.5 Repetition frequency frep Hz 120 50 5 Beam power P kW 219 91 630

CLIC parameters relevant for e+ source # of bunches per pulse # of positrons per bunch # of positrons per pulse Total charge (nC) Train pulse (ns) Current (A) Frequency (Hz) Entrance of Main Linac 311 4.1 x 109 1. 275x1012 242 207 1.17 50 At exit Pre- Damping ring 4.5 x 109 1.4 x 1012 265 1.3 Assuming ~ 90 % efficiency between the PDR and the Main Linac

CLIC conventional e+ source Parameter Unit CLIC (*) Primary Beam Energy (E) GeV 2 N e- /bunch (N) 109 13 Beam power kW 66 Linac frequency GHz 1.5 Bunch length (rms) (sz) mm 3 Parameter Unit CLIC (*) Target Material W75Re25 Length (4 c0) mm 14 Beam power deposited kW 16 Pulse energy density 1012 GeV/mm2 0.33 Energy lost per volume 1012 GeV/mm3 0.04 Deposited P / Beam Power % 25 (*) T. Kamitani, L. Rinolfi CLIC Note 465

Simulations for the Pre-Injector Linac (e+) For positrons at 200 MeV The normalised transverse emittances are: x,y = 9.2 10-3 rad.m  0.01 rad.m [at 1 ] E = 7 MeV and t = 17 ps.

Injector Linac entrance (e+) Assuming 95 % of transmission efficiency in the Injector Linac and 70% of capture efficiency in the PDR => N (e+) = 6.7 x 109 Parameter Unit CLIC 2007 Energy (E) GeV 0.2 No. of particles/bunch (N) 109 6.7 Bunch length (rms) (sz) mm 5 Energy Spread (rms) (sE) % 3.5 Longitudinal emittance (el) eV.m 35000 Horizontal emittance (gex) nm. rad 9.2 x 106 Vertical emittance (gey) Simulations have shown Yield = 0.31 e+/ e- GeV => N (e-) = 11 x 109 at 2 GeV If decelerating phase used => Yield = 0.39 e+/e- GeV

Simulations for the Injector Linac (e+) PLACET simulation results at Injector linac exit For positrons E mean = 2.4 GeV Ne+ = 6.4 x 109 / bunch DE = 17 MV/m Total distribution: sE = 1.5 % rms bunch length 5 mm For acceptance DE/E = 2 % FW Capture = 74 % of e+ rms bunch length 3.2 mm Longitudinal distribution obtained with PLACET A. Latina (CERN) => We have data to design the CLIC e+ Pre-Damping Ring

Polarization Polarisation is not a cheap option In addition to cost of conventional source: For undulator Layout of machine must accommodate: civil engineering for longer linac tunnel (cost and geologic limitations) photon dump e+ transfer line … Impact on operation and commissioning Impact on beam performance In addition to cost of conventional source: For Compton civil engineering for new ring laser system and optical cavity Laser power Design Compton ring e+ stacking

Experimental results obtained at ATF (KEK): Compton Polarization results Experimental results obtained at ATF (KEK): Compton 104 polarized e+ per bunch with 73% ± 15% ± 19% polarization Experimental results expected at E-166 (SLAC):Undulator 2 x107 polarized e+ per bunch with 40 - 80 % polarization

CLIC and ILC Damping rings (3 TeV) ILC (Nominal) Energy E GeV 2.424 5 Circumference C m 360 3230 Bunch population 109 4.4 20 Nb bunches / train - 311 2625 Bunch spacing ns 0.667 3 Final emittances ex,y nm, nm.rad 430, 4 8000, 20 rms bunch length sz mm 1.5 9 Final rms energy sE % 0.137 0.15 RF frequency MHz 1500 650 Repetition frequency frep Hz 50

The CLIC Injector complex (Undulator) BDS BDS e- Main Linac e+ Main Linac e- BC2 e+ BC2 12 GHz 12 GHz 1.8 km 12 GHz, 100 MV/m, 21 km Booster Linac 7 GeV e+ BC1 21 km e+ DR 3 GHz Booster Linac 7 GeV 2.424 GeV 20 km To the IP e- beam e- BC1 e- DR e- PDR Linac for e- 2.2GeV Injector 1.5 GHz 2.2GeV Injector Linac for e+ 150 GeV e- beam Target Ti alloy Pre-injector Linac for e+ Undulator ~100 m 1.5 GHz 2.424 GeV e-/e+ Target Laser Primary beam Linac for e- 200 MeV Pre-Injector Linac for e+ 200 MeV 3 TeV Undulator configuration for polarized e+ Unpolarized e- RF gun Keep Alive Source

CLIC layout from ILC scheme Undulator configuration for polarized e+ Injector Linac 2.2GeV 1.5 GHz 50 Hz 500 m

Undulator questions Coupling operation between e- and e+ e+ generated on the previous e- pulse. Constraints on the lengths for main linac + transport lines => multiple of DR circumference Today the linac length just fit to reach the Luminosity and the 3 TeV at the center of mass (with conventional e+ source). Estimate the reduced performance of the CLIC-IP Emittance growth from ey = 10 nm.rad ? Polarized e- through the undulator. What is the polarization and spin behavior after ?

The CLIC Injector complex (Compton) e+ Main Linac e- Main Linac e- BC2 e+ BC2 12 GHz 2.3 GV 12 GHz 2.3 GV 12 GHz, 100 MV/m, 21 km 12 GHz, 100 MV/m, 21 km 9 GeV 48 km 3 TeV Laser Compton configuration Booster Linac 6.6 GeV 3 GHz  360 m e+ BC1 e- BC1  10 m  10 m 3 GHz 162 MV 3 GHz 162 MV 2.424 GeV 360 m e+ DR 2.424 GeV 360 m e- DR e+ PDR and Accumulator ring e- PDR 2.424 GeV 2.424 GeV Injector Linac 2.2 GeV RF gun 1.5 GHz e- Drive Linac 1.3 GeV  150 m Compton ring 3 GHz e+ Target Pre-injector Linac for e+ 200 MeV Pre-injector Linac for e- 200 MeV Laser g DC gun Polarized e- Laser Stacking cavity 1.5 GHz 1.5 GHz  15 m  15 m

ILC - CLIC differences for Compton Bunch structure: CLIC has 5 x less bunch charge and 8 x less bunches per pulse: Should relax laser parameters Single one optical cavity Bunch spacing: CLIC has 4 x less bunch spacing: => Optical cavity more challenging Repetition frequency: CLIC has 10 x more repetition frequency:

Compton e+ source parameters CLIC ILC Energy 1.3 GeV Circumference 68 m 277 m RF frequency 1.5 GHz 650 MHz Bunch spacing 0.20 m 0.923 m Nb bunches stored 311 280 e- Bunch population 6.2 x 1010 Nb optical cavities 1 30 Photons/bunch/turn 4.3 x 109 5.8 x 1010 Photons (23-29 MeV) 6.9 x 108 1.36 x 1010 Pol. e+/bunch/turn 9.8 x 106 1.9 x 108 Nb injections/bunch 450 100 Total Nb e+/pulse 1.4 x 1012 5.3 x 1013 Total Nb e+/second 6.8 x 1013 2.7 x 1014

CLIC Compton ring E. Bulyak Parameters CLIC Energy 1.3 GeV RF frequency 1.5 GHz RF voltage 50 MV e- Bunch charge 10 nC e- bunch length at IP 5 mm Synchrotron losses 400 keV/turn Laser photon energy 1.164 eV Laser rms pulse length 0.9 mm Laser rms pulse radius 0.005 mm Laser pulse energy 600 mJ Full cycle (turns) 15000

CLIC Compton ring E. Bulyak Simulated yield = 0.07 photons/e-/turn Simulated photon yield as a function of turns number for continuous interaction with 600 mJ YAG laser pulse over 2500 turns

Compton configuration for polarized e+ e+ PDR and Accumulator ring CLIC scheme in 2007 Compton configuration for polarized e+ 2.424 GeV 360 m e+ DR 2.424 GeV 450 turns makes 311 bunches with 4.5x109 e+/bunch e+ PDR and Accumulator ring C = 68 m, 226 ns/turn, 311 bunches with 6.2x1010 e-/bunch Injector Linac 2.2 GeV 1.5 GHz RF gun Drive Linac 1.3 GeV 1.5 GHz Compton ring 3 GHz 50 Hz Pre-injector Linac for e+ 200 MeV g Stacking cavity g (23-29 MeV) 6.9x108 /turn/bunch 9.8x106 pol. e+/turn/bunch e+ target 1 YAG Laser pulse

Compton questions Can we get the requested laser power ? YAG laser into the Compton ring => large momentum acceptance (7-8%). Up to which value energy spread can be tolerated ? Is the present lattice design optimized for low and non linear momentum compaction ? What is the status of the feed-back on the laser, on the optical cavity ? Could we design a e+ Pre-Damping ring which allow e+ stacking and minimum transverse emittance as requested for the CLIC DR ?

CLIC scheme with Drive Beam ILC proposal from BNL(*) Parameters CLIC ILC proposal from BNL(*) Energy 2.3 GeV 6 GeV Current 100 A 4 A Nb bunches / train 3600 2625 e- Bunch population 5 x 1010 8 x 1010 Bunch charge 8 nC 13 nC Repetition fequency 50 Hz 5 Hz g to e+ conv. target 2GeV 100A e- beam g beam e+ beam (*) V. Yakimenko, POSIPOL 2006

Letter of Intent for EU-FP7-POSIPOL Design study Compton ring design Collection system design Multiple injection schemes Technological R&D High power & high repetition rate lasers Fabry-Perot optical cavities in pulsed regime Polarimetry Test Facility Experiments Validation at ATF & DANE

Conclusion 1) CLIC made major changes on their basic parameters. Therefore all parameters are under revision and could still be changed. 2) For the e+ conventional source, a solid study exist. The design of a e+ Pre-Damping Ring is urgently needed. 3) For polarized e+ based on Undulator, critical issues remain to be study. 4) For polarized e+ based on Compton, the scheme is more appropriate for a central injector complex and several parameters are relaxed compared with ILC. Nevertheless here also some critical issues remain to be study. 5) For polarized e+ based on head-on collision using the CLIC Drive Beam, study with new CLIC parameters has just started.