Positron Source for Linear Collider Wanming Liu 04/11/2013

Outline  Positron source requirements for LC  Undulator based positron source for ILC  Channeling radiation based positron source for CLIC  Undulator based positron source for CLIC  Common subjects 2

Requirements on positron source for LC  Be able to produce high intensity positron beam(Yield) –ILC: 2e10 per bunch (3e10 per bunch with 50% margin) –CLIC: Ecm=3TeV: 3.72e9 per bunch (4.3e9 at injector) Ecm=500GeV: 6.8e9 per bunch (7.8e9 at injector)  Polarization –30% for ILC TDR and >50% for ILC polarization upgrade –Non-polarized as in CLIC CDR

4 Undulator based positron source for ILC

5 Helical undulator: Can produce circularly polarized photon, good for polarized e+ source. Higher k, more high order harmonics contents. Smaller k, fewer high order harmonics, less photon flux, higher photon energy

6 Drive beam energy dependence study (no collimation)

Nominal parameters of ILC positron source

8 TeV upgrade –High drive beam energy, 500GeV which doubles the 250GeV TDR maximum photon beam energy increases by factor of 4 results in a larger energy spread and more positrons with unwanted polarization Smaller radiation angle results in smaller beam spot on target and thus higher energy deposition density –Solution New undulator, challenges exist in finding the parameter set with photon number spectrum similar to RDR undulator with 150GeV drive beam

9 With Fixed K=1 and different undulator period length Based on the above plot, u=4.3 is used for a more detail simulation to evaluate the energy deposition and impact on drive beam

Photon collimator for Polarization upgrade  A photon collimator is not required for the TDR baseline  As part of positron source upgrade study, DESY team developed a photon collimator design. With the designed photon collimator, positron source polarization can be increased from ~30% up to 50-60% depending on the colliding beam energy

Helical undulator based CLIC positron source for 500GeV Ecm stage m ILC RDR undulator 349m ILC RDR undulator lattice(effective length 250m) BDS 300m drift PPA 200MeV e-/e+/  Separation and merging into ERTML tunnel Accelerated to 2.86GeV and then inject into damping ring

Peak energy deposition estimation for CLIC undulator based positron source ILCCLIC 500GeVCLIC 3TeV Positron per bunch at IP (Ne+)2x x x10 9 Bunches per pulse (Nb) Bunch spacing (ns) Rep. Rate (Hz)550 Since bunch separation of CLIC is only 0.5ns, for 1st order approximation, one can consider all the bunches are striking at the same spot. And thus the peak energy deposition of undulator based positron source for CLIC can be estimated using the existing data for ILC undulator based positron source scaled by the charge density and sum by the number of bunch: 1.9(J/cm^3)*312*6.8/20=~202J/cm^3 or ~45J/g which is lower than ILC’s 67.5J/g for 250GeV drive beam energy As the charge has been lowered down to 3.72x10 9 for the 3TeV machine, the energy deposition will be even less. Timing and charge density comparison between ILC and CLIC

Common subjects: Optical Matching Device Conversion Target 14

15 Option:UCRL#Option:Additional Information Lawrence Livermore National Laboratory Pulsed flux concentrating magnet demonstrated 1 ms flat top with 3.5 T 15 Concentrating disk Energizing Coil Assembly Ramped pulser assembly  Demonstration of flat top at full field has been successful

16 Option:UCRL#Option:Additional Information Lawrence Livermore National Laboratory Encouraging initial results from the FerroTec seal for the rotating target wheel  Seal ran well for 450 hours before other components failed.  Repaired system is ready for further tests as funding allows 16 Water Union Motor Bearing Block Ferro- fluidic seal

Target area shielding and target remote handling  The target will be highly activated after one year of operation.  With the nominal 150kW photon beam, after 5000 hours of operation and 1 week of shutdown, the equivalent dose rate at 1m from the target wheel will be approximately 170 mSv/h. Concrete shielding of 0.8m thick around the target is sufficient fully to contain the radiation associated with the beam and with the subsequently activated materials.  A remote-handling system is used to replace the target, OMD and the 1 st 1.3m NC RF cavities.

Summary  A complete positron source design for ILC is available. Ecm upgrade and polarization upgrade options have been studied and documented.  An un-polarized positron source is currently documented in CLIC CDR  Since polarization will enhance the effective luminosity, initial efforts have been invested in porting ILC undulator based positron source into CLIC frames. 18