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ILC positron Source meeting
Wednesday 27 - Friday 29 September 2006 Rutherford Appleton Laboratory
Alessandro VariolaFor 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.,
LAL ActivitiesWhat are we doing?
• R&D on a high finesse optical cavity
• Posipol scheme
• Studies on channeling for the conventional solution
• 2 Goals: 1 operate a very high finesse Fabry-Perot
cavity in pulsed regime • 2 mirrors cavities Gain: 104-105
– 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)
Pound-Drever-Hall technique
Optical Scheme
AOMShifter EOM
Generator Demodulator
Feedback System
fc
fcwedge
fr mirror
fc GTI
fr
Pump laserVerdi 6W AOM MIRA 900P
FC
Coarse tuning: 1.Wedge
2. GTIFine tuning:
1. AOM-shifter
FREP
Coarse tuning: 1. Mirror motor
Fine tuning” 1. Mirror PZT
2. AOM
8 ADC:14 bits 105Msps
8 DAC : 14bits 125 Msps
fpga latency=60ns
Digital Feedback Scheme
Optical Setup at Orsay
Experiment setup.Laser & Cavity
installed
Present status
• Cavity aligned• Error signals
have been measured with a ’small finesse ’ cavity (3000)
Signal transmitted by the cavity
Errorsignal
Present activity: reduction of the noiseof the error signal and implementationof a feedback control of the small finessecavityManpower: 1 physicist, 2 engineers, 1 tech. Full time
– 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
• 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, Dax, Day, (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 w0 0: with 4m optical path, 6cm between 2 adjacent mirror centres
– xi=±0.1mm; axi=±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
LR R
Astigmatism
astigmatism
2D cavity
x,y versus z R=L(1-10-2)
Spher.mirrorsposition
mm
3D cavityastigmatismreduced
Z ‘strange’ TEM10 mode for the 3D cavity
y
x
S3 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 SiO2/Ta2O5 double layersCavity gain 105
S3=10-6 for q=5o and q=10mrad [4m optical path]
Checking the modes calculations:Spherical mirror ok. Not spherical mirror=> problems in the waist
4 mirrors non-plannar cavity
Cw laser diode inextended cavity config(optical feedback forseen)In test at Orsay since 2 weeks
Cavity vessel under construction in the LALworkshop
Manpower: 1PhD. & 1 technician full time
Conventional positron source
Positron damping ringLinac 6 GeV Linac 4.75 GeV
Target
Capture
Post Acceleration 250 MeV
Posipol scheme: we are working on a proposalfor a unique “lepton source” ERL based
1) We have a Post Doc !!!!!!
• 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
-0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04xmm0
50
100
150
200
250
300
0.030.020.01 0 0.01 0.02 0.03 0.04xmm0.3
0.2
0.1
0
0.1
0.2
0.3
xdarm
Scattered PhotonsXemittance
-2 -1 0 1 2 3xmrad0
200
400
600
800
1000
ERL solutionCan we compensate the charge reduction withbunch compression?
Polarised positron source – Compton cavities + ERL
Positron damping ringLinac 1.5 GeV Linac 4.75 GeV
Target
Capture
Post Acceleration 250 MeV
Compton cavities+ bunch compressor
Elecrton re-circulation
Positron damping ringLinac 1.5 GeV
Linac 4.75 GeV
Target
Capture
Post Acceleration 250 MeVCompton cavities+ bunch compressor
Elecrton re-circulation
100 ms 200 ms
cooling
4360s
5640s
282s
X 47
3s
3s
1 ms
cooling
282s
282s5640s
4360s
RF
1 ring filling @ 20 MHz
20 MHz : 60 bunches
3s
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 mAPeak current = (1.8nC x60) / 3 s = 36 mA
zoom
zoom
Electron polarised (unpolarised) sourcePolarised positron source – Compton cavities + ERL.(Splitting = Multi-injection in both rings)
Positron damping ring
Linac 1.5 GeV Linac 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 ringIf damping rings in the same location ….…new scenarios:
Electron polarised (unpolarised) sourceConventional & Polarised source – Compton cavities + ERL.Damping rings in the same location (splitting)
Positron damping ring
Linac 1.5 / 6 GeV Linac 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
IF DAMPING RINGS @ THE SAME LOCATION
Electron polarised (unpolarised) sourceConventional & 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 GeV Linac 4.75 GeV
Elecrton re-circulation
Electron damping ring
1 Complex !!!! Moreover, if we can re-circulate and split thefirst Linac we can avoid the second one
Advantage : e- e+ pol & unpolwith 1 LINAC of 10 GeV
IF DAMPING RINGS @ THE SAME LOCATIONElectron polarised (unpolarised) sourceConventional & 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 & unpolwith 1 LINAC of 6.25 GeV
• 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 studythe channeling option for the conventional source
• RESULTS OF WA 103 (10 GeV)• e+ yield in large momentum
(150 MeV/c) and angular (30°) domains.
• measured e+ yield in a (pL,pT) diagram; the case corresponds to a 8 mm crystal and a 10 GeV incident energy.
Example of absolute rate : W crystal [<111> orientation], 8mm thick, the yields have been measured in (pL,pT) domains..
For 6GeV : Yield plus ~ 15%Energy loss (heating) minus ~40 %
Outlook
• We are progressing in parallel with R&D of 2-mirrors and 4-mirrors cavities.
- 2mirrors = 1st error signal, low finesse. - 4mirrors = evaluation of the modes and
polarisation. Plans for the mechanical set-up. 1st 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