ILC RDR baseline schematic (2007 IHEP meeting) Collimator OMD 150GeV e- ~147GeV e- Target TAP (~125MeV) PPA(125-400MeV) PBSTR (Cryo-modules for boosting energy up to 5GeV) g dump e- dump Damping ring helical undulator g 2

Location of sources at the ILC RDR: SB2009

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.

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 150 125-250 e- energy loss in undulator 3.01 0.5-4.9 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

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).

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

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.

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

Capture Efficiency for RDR Undulator with Different Drive Beam Energy

Capture Efficiency for 250 GeV Drive Beam with Different K of Undulators FC QWT

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

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

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

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.

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

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

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

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

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

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.

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

PCAP PCAP is now in good shape

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=0.08649999999999999,VOLT=687499.924,PHASE=100,FREQ=1300000000,& 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=-0.08649999999999999 Then followed by a solenoid with a length of 8.65cm and K according to the expected beam energy PPASOL0: SOLE,L=0.08649999999999999,KS=1.2,ORDER=2 ………… PPASOL399: SOLE,L=0.08649999999999999,KS=0.37563839679799,ORDER=2

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=-2.8533,N_KICKS=20 QX2PPAT: KQUAD,L=0.15,K1=2.5641,N_KICKS=20 QX3PPAT: KQUAD,L=0.15,K1=-1.4611,N_KICKS=20 QX4PPAT: KQUAD,L=0.15,K1=0.9572000000000001,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)

PBSTR Matching section elements: Matching section beamline lattice Matching to PTRANH PBSTR1: 400MEV TO 1082.5649MEV PBSTR2: 1082.5649MEV TO 2507.0321 MeV PBSTR3: 2507.0321 MeV to 5GeV Matching section elements: DMAT11PB: DRIF,L=6.626114 DMAT12PB: DRIF,L=1.17866 DMAT13PB: DRIF,L=4.07932 DMAT14PB: DRIF,L=2.144358 DMAT15PB: DRIF,L=1.230926 QMAT11PB: QUAD,L=0.1,K1=-2.764554758 QMAT12PB: QUAD,L=0.1,K1=2.515452097 QMAT13PB: QUAD,L=0.1,K1=-3.231245599 QMAT14PB: QUAD,L=0.1,K1=2.901614891 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)

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= 1.634505504E+00 Qemit2LTR: QUAD, L=0.1,K1=-1.634505504E+00 DemithLTR: drift, L=2.0967

PTRANH, beta functions

PLTR

PLTR floor map Spin flipping

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?

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.

Energy deposition/accumulation on Target with RDR undulator

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

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(?) https://znwiki3.ifh.de/LCpositrons/TargetShockWaveStudy SLC positron target after decommissioning S. Hesselbach, Durham 11/11/2010 JGronberg, LLNL Global Design Effort 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

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.

High K, short period, 100GeV drive

TeV upgrade scenarios

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

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

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.

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

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.

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

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

Towards High Polarizations

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(125-400MeV) PBSTR (Cryo-modules for boosting energy up to 5GeV) g dump e- dump Damping ring helical undulator g

Photon Collimator Recommendation from ILC positron source meeting in Durham (2009) was to include a tungsten/graphite collimator of radius 2mm. https://znwiki3.ifh.de/LCpositrons/CollimatorDesign Same specification works for SB2009 (2.5kW in collimator) A. Ushakov, DESY

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

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

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.

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)