1. ILC RDR baseline schematic (2007 IHEP meeting)
Collimator
OMD
150GeV e-
~147GeV e-
Target
TAP
(~125MeV)
PPA( MeV)
PBSTR (Cryo-modules for boosting energy up to 5GeV)
g dump
e- dump
Damping ring
helical undulator g 2

2. Location of sources at the ILC
RDR:
SB2009

3. Parameters: Optimize the positron yields for known technologies:
Superconducting helical undulator.
Undulator parameter: K=0.92, lu=1.15cm
Capturing magnets
Optical matching device: FC and ¼ wave transformer
Targets: 0.4 X0 Ti, W and liquid Pb also considered (not covered in this talk).
Damping ring acceptance
Energy spread < 1% (possibly 2%)
emittance_x + emittance_y < 0.09 m-rad
Goal:
Achieve yield of 1.5 positrons per electron in the drive beam.
No polarization required.
Polarization required.

4. Summary Parameters (Sabine Riemann, 2011)
RDR
SB2009
Units
e+ per bunch at IP
2 x 1010
1 to 2 x 1010
Bunches per pulse
2525
1312
e+ energy (DR injection) 5
GeV
DR transverse acceptance
0.09
m-rad
DR energy acceptance
±0.5
± 0.5 %
e- drive beam energy
150
e- energy loss in undulator
3.01
Undulator period
11.5 mm
Undulator strength
0.92
Active undulator length
147 (210 after pol. Upgrade)
231 max. m
Field on axis
0.86 T
Beam aperture
5.85
Photon energy (1st harm.) 10
1.1 (50 GeV)
28 (250 GeV)
MeV
Photon beam power
131
Max: 102 at 150 GeV kW
Target material
Ti-6%Al-4%V
Target thickness 14
Target power adsorption 8
PEDD in target
Dist. Undulator center - target
500
e+ Polarization 34 22 5 5

5. Status of the critical hardware components
4 meter cryo-module, two 1.7m long RDR undulator. (Completed, STFC/RAL/Daresbury)
Target wheel prototype design and test. (Lancaster/Cockcroft/STFC/LLNL)
Rotating vacuum seal prototype test. (LLNL, ongoing, initial test conducted)
Capturing RF structure. (SLAC, Completed)
Flux Concentrator prototype design. (LLNL, ongoing)
New short period, high K undulator. (Cockcroft/STFC, on-going, material availability issue).

6. ILC Positron source optimization: Cases Studied:
Reference Input Parameters:
Undulator parameter: K=0.92, lu=1.15cm
Target: 0.4 X0 Ti
Drift between undulator and target: 400m
Photon collimator: None
OMD:
Flux Concentrator Capturing (137 m long Undulator).
Quarter Wave Transformer Capturing (231 m long undulator).
Undulator Impacts on Drive Beam
Energy Spread and,
Emittance
Target Energy Deposition.
Path toward higher polarizations
Photon collimators

7. A pulsed flux concentrator
Pulsing the exterior coil enhances the magnetic field in the center.
Needs ~ 1ms pulse width flattop
Similar device built 40 years ago. Cryogenic nitrogen cooling of the concentrator plates.

8. Conditions RF: 15MV/m for 1st meter and 8MV/m for the rest
OMD: FC, varying B0 with fixed length of 14cm
Capture evaluated at ~125MeV

9. Capture Efficiency for RDR Undulator with Different Drive Beam Energy

10. Capture Efficiency for 250 GeV Drive Beam with Different K of UndulatorsFC
QWT

11. Yield and Pol
250GeV drive beam
RDR with different drive beam

12. Explanation of Pol-B0 relation
As displayed in the plots, particles with lower energy tends to have bigger emitting angle and lower polarization.
When B0 get smaller, more lower energy particles will pass through the barrier created by the ramping up of B field and being captured. Meanwhile, more particles with higher energy but bigger angle will escape the capture as the field get weaker. That’s why lowering B0 will lower the polarization of captured beam initially.
When B0 get even smaller, the low energy and bigger emitting angle particles will escape the capture and then the captured positron beam polarization starts going up

13. RDR undulator, 250GeV 60% Pol. possibility
Yield
Pol.
With FC having B0 ~2.5T, 60% polarization and 1.5 yield can be achieved with photon collimator having an iris of ~0.55mm in radius using 231m RDR undulator

14. Yield Calculations Using RDR Undulator Parameters (137 meter and FC without photon collimators )
Drive beam energy
Yield
Polarization
Required Undulator Length for 1.5 Yield
Emittance Growth X/Y for 1.5 Yield*
Energy Spread from Undulator for 1.5 Yield
50 GeV
0.0033
0.42
Very long
100 GeV
0.2911
0.39
685 m
150 GeV
1.531
0.34
137 m
~ -2.5%/-1.6%
0.17%
200 GeV
3.336
0.27
61 m
250 GeV
5.053
0.23
40 m
~-1%/-0.4%
0.18%
* No Quads misalignment included.

15. Emittance growth due to BPM to Quad misalignments -- From Jim Clark’s report

16. RDR undulator, Quarter Wave Capturing Magnet
Undulator: RDR undulator, K=0.92, lu=1.15cm
Length of undulator: 231m
Target to end of undulator:400m
Target: 0.4X0, Ti
Drive beam energies: 50GeV to 250GeV
Reference: 150 GeV 17

17. ¼ wave solenoid ANL ¼ wave solenoid simulations
Low field, 1 Tesla on axis, tapers down to 1/2 T.
Capture efficiency is only 25% less than flux concentrator
Low field at the target reduces eddy currents
This is probably easier to engineer than flux concentrator
SC, NC or pulsed NC?
ANL ¼ wave solenoid simulations
The target will be rotating in a B field of about 0.2T
W. Liu 18

18. Yield and polarization of RDR configuration for different drive beam energy
Energy lost per 100m
Energy lost for 1.5 yield
50GeV
~225MeV
N/A
100GeV
~900MeV
~9.9GeV
150GeV
~2GeV
~4.6GeV
200GeV
~3.6GeV
~3.7GeV
250GeV
~5.6GeV
~3.96GeV
Drive beam energy
Yield
Polarization
50GeV
0.0041
0.403
100GeV
0.3138
0.373
150GeV
1.572
0.314
200GeV
3.298
0.265
250GeV
4.898
0.221 19

19. OMD comparison Same target
Beam and accelerator phase optimized for each OMD
OMD compared:
AMD
Flux concentrator
¼ wave transformer
Lithium lens
OMD
Capture efficiency
Immersed target, AMD
(6T-0.5T in 20 cm)
~30%
Non-immersed target, flux concentrator
(0-3.5T in 2cm, 3.5T-0.5T 14cm)
~26%
1/4 wave transformer
(1T, 2cm)
~15%
0.5T Back ground solenoid only
~10%
Lithium lens
~29% 20

20. Yield calculations
So far, we calculated the yield of 1.5 at 125 MeV, ANL and DESY results are all in agreement.
Ongoing calculation for different scenarios.
We are working on a lattice design that will accelerate and transport beam to 400 MeV first and then 5 GeV with low losses. Progressing slow but positive. Using the RDR lattice from SLAC as a starting point, this lattice should be simpler, no long transport line as in RDR. Need to be finalized before the TDR.

22. PTAPA
OMD
Target
OMD:
Flux concentrator: Physical length ~14cm, With ~0.5T on target surface, and decay adiabatically from 3.5T at 2cm from target down into the 0.5T background solenoid field at 14cm.
QWT: Physical length ~20cm, peak field ~1T.
Standing wave linac: 11 cells, p mode, 15MV/m, length 1.27m each, total numbers: 2
Traveling wave linac: 50 cells, 3p/4 mode, 8MV/m, 4.3m long each, total numbers: 3
Total length of tunnel reserved: 17m per Beno’s drawing,
Minimum length of tunnel needed: ~16m

23. PCAP
PCAP is now in good shape

24. PPA 0.5T solenoids 8x 4.3m long TW linacs
Beamline lattice for MAD/elegant
The Lattice implementation in MAD/elegant input divided the into short pieces with length of about 8.65cm:
PPAKK1: RFCA,L= ,VOLT= ,PHASE=100,FREQ= ,&
CHANGE_P0=1,FIDUCIAL="LIGHT",END1_FOCUS=1,END2_FOCUS=1,N_KICKS=10
Each piece is followed by a back drift with the same length,8.65cm:
BACKD: EDRIFT,L=
Then followed by a solenoid with a length of 8.65cm and K according to the expected beam energy
PPASOL0: SOLE,L= ,KS=1.2,ORDER=2
…………
PPASOL399: SOLE,L= ,KS= ,ORDER=2

25. PTRAN Matching section: Matching section
FODO lattice with earth bend every 16.8m to match to the earth curvature
Matching section:
consists of 4 quads and 4 drift as defined in the following:
QX1PPAT: KQUAD,L=0.15,K1= ,N_KICKS=20
QX2PPAT: KQUAD,L=0.15,K1=2.5641,N_KICKS=20
QX3PPAT: KQUAD,L=0.15,K1= ,N_KICKS=20
QX4PPAT: KQUAD,L=0.15,K1= ,N_KICKS=20
DX1PPAT: EDRIFT,L=0.2
DX2PPAT: EDRIFT,L=0.3
DX3PPAT: EDRIFT,L=3.5
DX4PPAT: EDRIFT,L=6
The lattice is defined as:
LINE=(DX1ppat,VCOR,QX1ppat, QX1ppat, DX2ppat,HCOR,QX2ppat, QX2ppat, DX3ppat,&
VCOR,QX3ppat, QX3ppat, DX3ppat,HCOR,QX4ppat, QX4ppat, DX4ppat)

26. PBSTR Matching section elements: Matching section beamline lattice
Matching to PTRANH
PBSTR1: 400MEV TO MEV
PBSTR2: MEV TO MeV
PBSTR3: MeV to 5GeV
Matching section elements:
DMAT11PB: DRIF,L=
DMAT12PB: DRIF,L=
DMAT13PB: DRIF,L=
DMAT14PB: DRIF,L=
DMAT15PB: DRIF,L=
QMAT11PB: QUAD,L=0.1,K1=
QMAT12PB: QUAD,L=0.1,K1=
QMAT13PB: QUAD,L=0.1,K1=
QMAT14PB: QUAD,L=0.1,K1=
Matching section beamline lattice
mat1pb: LINE=(QFPT,QFPT, Dmat11pb,vcor,Qmat11pb,Mmat11pb,Qmat11PB,Dmat12pb,&
hcor,Qmat12pb,Mmat12pb,Qmat12PB,Dmat13pb,vcor,Qmat13pb,Mmat13pb,Qmat13PB, &
Dmat14pb,hcor,Qmat14pb,Mmat14pb,Qmat14PB, Dmat15pb)

27. PTRANH Simple FODO lattice to transport the beam to PLTR
The lattice is defined as:
PTRANH: LINE= (117*(DemithLTR,hcor,Qemit1LTR,Qemit1LTR,DemithLTR,DemithLTR,&
vcor,Qemit2LTR,Qemit2LTR,DemithLTR))
The elements are defined as:
Qemit1LTR: QUAD, L=0.1,K1= E+00
Qemit2LTR: QUAD, L=0.1,K1= E+00
DemithLTR: drift, L=2.0967

28. PTRANH, beta functions

29. PLTR

30. PLTR floor map
Spin flipping

31. Spin rotation flipping in PLTR
A switching magnet will switch the beam to either solenoid (5 GeV)
Solenoid Parameter:
B=3.16 Tesla; L=8.3 meter
Questions: Flipping scenarios? Fast, slow, pulse to pulse and within the pulse?

32. Longitudinal distribution of e+ at treaty point
Need to add collimators at PCAP to clean up those e+ outside the damping ring acceptance window. As a result, some good e+ will be collimated too.

33. Energy deposition/accumulation on Target with RDR undulator

34. Density of accumulated deposit energy (for RDR rotating target)
1.5 yield / 3e10 e+ captured,
Ti target (density=4.5 g/cm^3)
Thickness for highest yield
(X0)
Energy deposition per bunch (J.)
Average power (KW)
Peak energy density
(J/cm^3) ;
(J/g)
150GeV,FC (137 m)
0.4
0.72
9.5
348.8
77.5
250GeV, FC (40 m)
0.342
4.5
318.8
70.8
150GeV, QWT (231 m)
1.17
15.3
566.7
126
250GeV, QWT (76 m)
0.61
8.01
568.6
126.4

35. Shockwaves in the target
Energy deposition causes shockwaves in the material
If shock exceeds strain limit of material chunks can spall from the face
The SLC target showed spall damage after radiation damage had weakened the target material.
Initial calculations from LLNL had shown no problem in Titanium target
Two groups are trying to reconfirm result
FlexPDE (S. Hesselbach, Durham  DESY)
ANSYS (L. Fernandez-Hernando, Daresbury)
No definitive results yet
Investigating possible shockwave experiments
FLASH(?)
SLC positron target after decommissioning
S. Hesselbach, Durham
11/11/2010 JGronberg, LLNL
Global Design Effort 36

36. Remote Handling
Norbert Daresbury had an initial layout a few years ago.
Activation evaluation done by Andriy Ushakov.
For TDR, needs to consider RH scenarios, such as:
Changeover times (requirement ties in with lifetime of kit in RH)
Replacement of pillow seals?
Need engineered design compatible with source layout (remove inconsistencies!)
If yield increases then RH not needed (limited only?)
We will concentrate this in the next few months. 37

37. High K and short period  Undulator Option
Important to SB2009 scenarios.
Assumptions:
Length of undulator: 231m
Drive beam energy: 100GeV
Target: 0.4X0, Ti
Photon Collimation: None
Drift to target: 400m from end of undulator
OMD:FC, 14cm long, ramping up from 0.5T to over 3T in 2cm and decrease adiabatically down to 0.5T in 12cm.
The undulator development is challenging:
Difficult to obtain the required wires (Nb3Sn), supplier issues.

38. High K, short period, 100GeV drive

39. TeV upgrade scenarios

40. Goal Assumptions Approach:
A reasonable scheme for the 1 TeV option without major impact on the ILC configuration.
Assumptions
Drive beam energy: 500 GeV
Target: 0.4 X0 Ti
Drift from end of undulator to target: 400m (longer drift helps, but fix it for now).
OMD: QWT
Approach:
Longer undulator period

41. Radiated Photo parameters from beam passing through a helical undulator:
The 1st Harmonic critical energy is approximately inversely proportional to the square of K when K goes higher and also inversely proportional to length of undulator period. Since K is proportional to the length of undulator period, thus the 1st harmonic critical energy is approximately inverse proportional to the cubic of the length of undulator period.
The 1st Harmonic critical energy is proportional to the square of gamma
When drive beam increased up to 500GeV, we can increase the length of undulator period to maintain photon spectrum and thus minimize the change of design. 42

42. Fixed B field at 0.85T and increase the period length to 4cm
Simulation with 400 harmonics shows that with a collimator of 1.5mm radius, a yield of 2.8 and polarization of 30% can be achieved.
Simulation also shows that 859kW of photon beam will be generated per 3e10 e+ per bunch (1.5 yield). The photon beam passing through the collimator iris will be 243kW and the energy deposition will be about 7.5kW. The photon power stopped by the collimator will be about 616kW
The energy lost in drive beam will be about 44.6GeV for 231m undulator or about 19.3GeV per 100m undulator.
Solution: Lower B field so the total energy loss will be ~ 5 GeV per electron.

43. With Fixed K=1 and different undulator period length (QW capturing)
Based on the above plot, lu=4.3cm is used for a more detail simulation to evaluate the energy deposition and impact on drive beam

44. Preliminary results about polarization
K=1, lu=3cm
30% polarization can be achieved by using a photon collimator with iris of about 0.9mm with K=1 and lu=3cm.

45. TeV upgrade Scenarios lu (cm) Photon beam power (kW)
Parameters for 1.5 of positron yield using fixed K=1 with different undulator period
lu (cm)
Photon beam power (kW)
Power deposition (kW)
Drive beam energy lost (GeV)
Undulator length required (m) 3
206
7.19
4.91
124 4
186
7.84
4.44
198
4.3
181
7.94
221 5
176
8.37
4.19
289 6
166
8.76
3.88
387 7
170
9.80
4.05
549 8
10.34
3.94
697

46. Accumulated effect of energy deposition -bunch separation is 356ns and target is rotating at 900RPM
The accumulated energy deposition in the rotating target (900RPM, 2m diameter) is about 1050 J/cm^3 while the number for RDR is 566J/cm^3. To bring it back to the RDR value, one can consider increase the bunch separation which reduce the number of bunch to 1312 per pulse with 712ns bunch separation or double the drift from undulator end to target

47. Towards High Polarizations

48. Most sensitive parameter: Transverse photon distribution:
Photon Collimation would eliminate unwanted off axis photons that have low polarization.
Other parameters (drive beam energy and low K undulator) also have influences, but not dominate (skipped from this presentation).
Collimator
OMD
150GeV e-
~147GeV e-
Target
TAP
(~125MeV)
PPA( MeV)
PBSTR (Cryo-modules for boosting energy up to 5GeV)
g dump
e- dump
Damping ring
helical undulator g

49. Photon Collimator
Recommendation from ILC positron source meeting in Durham (2009) was to include a tungsten/graphite collimator of radius 2mm.
Same specification works for SB2009 (2.5kW in collimator)
A. Ushakov, DESY

50. Collimator design studies
- heat loads (temperatures) for different collimator designs are simulated
-> collimator design is improved to withstand the heat load
- time dependent heat and structural loads are simulated with ANSYS software
graphite collimator
simulation
theoretical max
temperature
800 K
~ 4000 K
deformation
45 mm -
stress
10 MPa
20-70 MPa

51. Polarization upgrade
231m RDR undulator, 150GeV drive beam, ¼ wave transformer
With QWT, with a photon collimator to upgrade the polarization to 60%, the positron yield will drop to ~0.8
With QWT, with a photon collimator to upgrade the polarization to 60%, the positron yield will drop to ~0.8
Drive beam energy
Energy lost per 100m
Energy lost for 1.5 yield and 60% polarization
150GeV
~2GeV
~8.8GeV 52

52. Issues with ILC positron sources
Risk assessments for the e+ system:
Undulator (OK, more RD needed for different scenarios other than Baseline)
Photon Collimators (good progress made, need a real design)
Capturing magnets (design done, prototyping on the way)
Target (Tested, other engineering issues, OK)
Pre-accelerator (done)
RH (under discussion).
Lattice (ongoing, progressing, shouldn’t be to much risks).
Chicane and positron collimator (issues to be resolved, but low risks)
Sources TeV upgrade seems to be OK.

53. From Marc Ross’s Excel Table
Flux Concentrator or Quarter Wave Transformer
Would like to adopt the Flux Concentrator
Primary decision to be resolved at BTR - does the planned R & D justify that choice?
PLTR design coupled with DR acceptance
Integrated optics to be documented
yield ‘budget’
to be re-compiled and documented
design work and simulation needed
E+ spin rotator
System should be able to accommodate e+ spin rotator
Current lattice includes rotators. Decision needed on the e+ spin flipping system.
10Hz operation dump
Schematic design required; adopt the most practical
Adds an additional high powered dump to system: that now makes six!
Auxiliary source
Needs specification; suggestion: 2%, very low power
Primary discussion at BTR: what exactly does this look like and for what will we use it
HLRF scheme for injector linacs
Choose HLRF alternate: KCS, DRFS, RDR; integrate requirements. (also for e- source)