Summaries, Question Responses and Supporting Documents
Updated 6 October 2005
Accelerator WG3a workspace from Snowmass
Summary
Electron:
Baseline recommendation is DC gun with NEA GaAs photo-cathode. There is no vital configuration to make polarized electron beam other than this recommendation at this moment.
Baseline is 120 kV DC gun with GaAs/GaAsP Strained Super-lattice photo-cathode. Drive laser is seeded with Ti:Sapphire pulse train generator pumped by Nd:YLF.
No alternative recommendations, because the alternative proposals are still pre-mature and not significantly beneficial as ILC electron source.
Positron:
Baseline recommendation is Helical Undulator because the undulator based source offers the greatest certainty of meeting the required positron source design specification.
The undulator is placed at the end of electron linac (250 GeV at Phase 1, 500GeV at phase 2). The high energy electron beam prior to the collision passes through the undulator, making high energy gamma up to 30 MeV. This gamma is then converted into e+ with a rotating Ti-alloy target with 100m/s tangential speed. The undulator length will be up to 200m. The e+ beam is transported to the positron arm by-passing the IP.
Alternative Recommendations:
a) Conventional Source as a backup because the undulator based system is never built and might have unknown difficulties. In addition, the system is reliable if the rotating target is established. This system is independent from the electron linac.
Positron is generated with 6 GeV drive electron beam and W-Re alloy 4 radiation length rotating target. For single target system, the tangential rotation speed will be 360m/s at the fatigue limit, but it could be lower with multi-target system.
b) Another alternative recommendation is Laser Compton Based Positron Source because this system is an independent system from the electron side giving a large flexibility and can make high intensity polarized positrons. However, several critical R&Ds have to be carried out to implement it.
In a high-current electron storage ring with 1/10 circumference of main DR (Compton Ring), 30 laser cavities are placed to make high energy gamma up to 30MeV with the laser beam interaction. This gamma is converted into e+ as same as Undulator scheme, but the intensity is 1/100. The e+ bunches will be stacked into a same bucket in main DR 10 times. This cycle is repeated 10 times with 10ms intervals for the beam damping.