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