1. ILC positron Source meeting Wednesday 27 - Friday 29 September 2006 Rutherford Appleton Laboratory Alessandro Variola For the L.A.L. Orsay group Brisson V., Chehab R., Chiche R., Cizeron R., Fedala Y., Jacquet-Lemire M., Jehanno D., Soskov V., Variola A., Vivoli A., Zomer F.,

2. LAL Activities What are we doing? R&D on a high finesse optical cavity Posipol scheme Studies on channeling for the conventional solution

3. 2 Goals: 1 operate a very high finesse Fabry-Perot cavity in pulsed regime 2 mirrors cavities Gain: 10 4 -10 5 –Started in sept 2005 2 reduction of the laser beam size (waist) 4 mirrors non-planar cavity –Setup started in sept. 2006 Present R&D at Orsay (funded by EUROTEV & IN2P3:CNRS)

4. Pound-Drever-Hall technique

5. Optical Scheme AOM Shifter EOM Generator Demodulator Feedback System fcfc f c wedge f r mirror f c GTI frfr Pump laser Verdi 6W AOM MIRA 900P F C Coarse tuning: 1.Wedge 2. GTI Fine tuning: 1. AOM-shifter F REP Coarse tuning: 1. Mirror motor Fine tuning” 1. Mirror PZT 2. AOM

6. 8 ADC: 14 bits 105Msps 8 DAC : 14bits 125 Msps fpga latency=60ns Digital Feedback Scheme

7. Optical Setup at Orsay

8. Experiment setup. Laser & Cavity installed Present status

9. Cavity aligned Error signals have been measured with a ’small finesse ’ cavity (3000) Signal transmitted by the cavity Error signal Present activity: reduction of the noise of the error signal and implementation of a feedback control of the small finesse cavity Manpower: 1 physicist, 2 engineers, 1 tech. Full time

10. –4 mirror cavities (  R&D in 2006-2007) The mechanical tolerances The eigen modes The polarisation transport –2 extra topics (  possible futur R&D) Effect of strong laser beam focusing on cavity modes Effect of high beam power inside the cavity

11. Mirror misalignment sources –Residual precision of the installation: ~1/100 mrad, 1/100 mm –Environmental motion (vibrations, thermal…): <mrad, mm 5 degrees of freedom per mirror Dx, Dy, Dz, Da x, Da y, (of the mirror’scentres) CALCULATION: Compute the max. displacement of the optical axis for all combinations of misalignments.  rel. precision check~10 -3 Results for w 0  0: with 4m optical path, 6cm between 2 adjacent mirror centres –  x i =±0.1mm;  a xi =±0.1mrad –plane mirrors: 0.6mm on spherical mirrors: 1.1mm At beam waist: 0.3mm: 0.5mrad  High mechanical stability [as expected] –Negligible effects of the environment a priori Mechanical tolerances for 4 mirrors cavity

12. L R R Astigmatism astigmatism 2D cavity  x,  y versus z R=L(1-10 -2 ) Spher. mirrors position mm 3D cavity astigmatism reduced

13. ZZ ‘strange’ TEM10 mode for the 3D cavity y x

14.   S 3 much less sensitive to mirror disorientations : 4 mirror non planar cavity = good solution for waist and polarisation 3D cavity in a `quasi cubic’ configuration 21 SiO 2 /Ta 2 O 5 double layers  Cavity gain  10 5   S 3 =10 -6 for q=5 o and  q=10mrad [4m optical path] Checking the modes calculations: Spherical mirror ok. Not spherical mirror=> problems in the waist

15. 4 mirrors non-plannar cavity Cw laser diode in extended cavity config (optical feedback forseen) In test at Orsay since 2 weeks Cavity vessel under construction in the LAL workshop Manpower: 1PhD. & 1 technician full time

16. Conventional positron source Positron damping ringLinac 6 GeVLinac 4.75 GeV Target Capture Post Acceleration 250 MeV Posipol scheme: we are working on a proposal for a unique “lepton source” ERL based 1) We have a Post Doc !!!!!!

17. Laser power density 1.90349132D+21 Laser pulse Energy [Joule]= 6.00000000D-01 Laser pulse length [m]= 2.40000000D-04 Laser pulse wavelength [m= 1.06000000D-06 Laser waist size [m]= 1.00000000D-05 Laser Rayleigh length [m]= 2.96376665D-04 Compton cut off [x beam energy]= 2.27627018D-02 Beam Energy [eV]= 1.30000000D+09 Particles per bunch9.36000000D+09 Collision beta function x= 1.60000000D-01 Collision beta function y= 1.60000000D-01 Beam size sigma x [m] = 1.00000000D-05 Beam size sigma y [m] = 1.00000000D-05 Beam length sigma z [m] = 2.00000000D-04 Emittance x= 6.25000000D-10 Emittance y= 6.25000000D-10 Energy Spread= 3.00000000D-03 Collision angle [rad]= 8.72664626D-02 *********************************** Beam STATISTICS +++Right-going photon 25034 macro particles 1.562D+09 real Average (t,x,y,s) 4.000D-04 5.161D-08 1.431D-08 4.002D-04 m R.m.s. (t,x,y,s) 1.138D-17 8.025D-06 4.693D-06 1.711D-04 m Min (t,x,y,s) 4.000D-04 -3.212D-05 -2.013D-05 -2.618D-04 m Max (t,x,y,s) 4.000D-04 3.005D-05 2.815D-05 1.070D-03 m Average (En,Px,Py,Ps) 1.474D+07 1.699D+01 3.052D+01 1.474D+07 eV R.m.s. (En,Px,Py,Ps) 9.279D+06 2.658D+03 2.672D+03 9.279D+06 eV Min (En,Px,Py,Ps) 3.095D+02 -7.827D+03 -8.248D+03 3.082D+02 eV Max (En,Px,Py,Ps) 2.987D+07 8.207D+03 8.557D+03 2.987D+07 eV Stokes (|Xi|,Xi1,Xi2,Xi3) 0.00709 0.00128 0.00675 0.00175 ERL solution Can we compensate the charge reduction with bunch compression?

19. Polarised positron source – Compton cavities + ERL Positron damping ringLinac 1.5 GeVLinac 4.75 GeV Target Capture Post Acceleration 250 MeV Compton cavities + bunch compressor Elecrton re-circulation

20. Positron damping ring Linac 1.5 GeV Linac 4.75 GeV Target Capture Post Acceleration 250 MeV Compton cavities + bunch compressor Elecrton re-circulation 100 ms 200 ms cooling 4360  s 5640  s 282  s X 47 3s3s 3s3s 1 ms cooling 282  s 5640  s 4360  s RF 1 ring filling @ 20 MHz 20 MHz : 60 bunches 3s3s a possible example ERL : 100 re injection if 1 damping ring scheme. 50 if double damping ring scheme Average current = (1.8 nC x 282000 x 5 A) = 2.5 mA Peak current = (1.8nC x60) / 3  s = 36 mA zoom

21. Electron polarised (unpolarised) source Polarised positron source – Compton cavities + ERL. (Splitting = Multi-injection in both rings) Positron damping ring Linac 1.5 GeVLinac 4.75 GeV Target Capture Post Acceleration 250 MeV Compton cavities + bunch compressor Elecrton re-circulation Electron damping ring Linac 5 GeV The first 1.5 GeV linac can be substituted with a 6 GeV one to have both sources Two sources. One source every damping ring If damping rings in the same location ….…new scenarios:

22. Electron polarised (unpolarised) source Conventional & Polarised source – Compton cavities + ERL. Damping rings in the same location (splitting) Positron damping ring Linac 1.5 / 6 GeVLinac 4.75 GeV Electron re-circulation Electron damping ring Linac 5 GeV But positron injection takes not more than 100 msec. The remaining 100 msec are enough for electron cooling, so we can split electron and positron injection in time and unify the electron and positron linacs : Advantage : e+ pol & unpol

23. IF DAMPING RINGS @ THE SAME LOCATION Electron polarised (unpolarised) source Conventional & Polarised source – Compton cavities + ERL. Damping rings in the same location (splitting…why not also for the conventional solution) Positron damping ring Linac 1.5 / 5 / 6 GeVLinac 4.75 GeV Elecrton re-circulation Electron damping ring 1 Complex !!!! Moreover, if we can re-circulate and split the first Linac we can avoid the second one Advantage : e- e+ pol & unpol with 1 LINAC of 10 GeV

24. IF DAMPING RINGS @ THE SAME LOCATION Electron polarised (unpolarised) source Conventional & Polarised source – Compton cavities + ERL. Damping rings in the same location (splitting) => e +,e - pol / non pol Positron damping ring Linac 1.25 / 1.5 GeV Electron re-circulation Electron damping ring Linac 3.5 GeV Linac 1.25 GeV Positron re-circulation Disrupted electrons and polarised positrons are re-circulated in the same train (deceleration for electrons and acceleration for positrons) All this complex can be accommodated inside the damping rings Advantage : e - e + pol & unpol with 1 LINAC of 6.25 GeV

25. UNPOLARIZED SOURCES - an amorphous target with high Z submitted to an unpolarized e- beam of high energy [conventional] - a crystal source made of a crystal aligned on one of its axes (radiator) and of an amorphous W disk (converter) placed after it. = Hybrid THE Hybrid SOURCE Pair production in the same crystal or in an amorphous disk put after the crystal (preferably) The beam aligned on one of the crystal axes (where the potential is strong). Experiments made at CERN, KEK Simulations showed less deposited energy than in equivalent (e+ yield) amorphous target In the future : we would like to study the channeling option for the conventional source

26. RESULTS OF WA 103 (10 GeV) e+ yield in large momentum (150 MeV/c) and angular (30°) domains. measured e+ yield in a (p L,p T ) diagram; the case corresponds to a 8 mm crystal and a 10 GeV incident energy. Example of absolute rate : W crystal [ orientation], 8mm thick, the yields have been measured in (p L,p T ) domains.. For 6GeV : Yield plus ~ 15% Energy loss (heating) minus ~40 %

27. Outlook We are progressing in parallel with R&D of 2-mirrors and 4-mirrors cavities. - 2mirrors = 1 st error signal, low finesse. - 4mirrors = evaluation of the modes and polarisation. Plans for the mechanical set-up. 1 st test with CW laser We are starting to evaluate a new scheme for the Compton source. The new idea seems promising In the future we would like to study the impact of the channeling for the conventional source