1. 29/10/09 Positron Workshop 1 Working Assumptions for Low Energy Operations Jim Clarke ASTeC & Cockcroft Institute Daresbury Laboratory

2. 29/10/09 Positron Workshop 2 Background For SB2009 the undulator is moved to the end of the linac The ILC still needs to operate over a wide energy range The yield of positrons is not constant with electron energy We need a specification for the yield so that we can design the source appropriately I asked for guidance on this at ALCPG09 This talk will discuss the provisional guidance I have received …

3. Provisional Guidance (from PMs) The nominal scheme is used for operation until the beam energy is reduced below the point where the undulator source effective positron yield is below 0.5. For operation below that point, the ILC will use an alternating pulse scheme (2.5Hz). PMs Suggest: –Pulsed steering magnets are used to correct the launch into the undulator so that there is no natural difference between the high energy (e+ production) and low energy (collision) beam trajectory due to the upstream linac curvature. Of course, the undulator itself is aligned along a laser straight line pointing at the target. The pulsed magnets will have a 2.5 Hz periodic excitation waveform. –Pulsed trajectory correction magnets may be needed within the undulator. –Pulsed dipole magnets are used to extract the charged beams between the downstream end of the undulator and the target. There are obvious MPS and magnet/power supply design issues with this sub-system, but it should be feasible. The high energy beam (e+ production beam) should be dumped in the full power BDS tune-up dump. 29/10/09 Positron Workshop 3

4. SB2009 Layout Electron beam layout 29/10/09 Positron Workshop 4 e- side starting from main Linac exit  Fast abort line Photon target + remote handling 400m DC Tuning line Undulator Dogleg Sacrificial collimators + chicane to detect off energy beams Interaction Point Deepa Angal-Kalinin/James Jones

5. SB2009 Changes Low energy electrons transported to IP via undulator and full BDS 29/10/09 Positron Workshop 5 e- side starting from main Linac exit  Fast abort line, for which beam? Both? Photon target + remote handling DC Tuning line Undulator, also with pulsed steering magnets? Dogleg Pulsed magnets here to compensate trajectory errors Interaction Point High energy electron beam transported to Tuning line dump

6. Yield vs Energy Yield of 1.5 at 150 GeV Yield of 0.75 at ~125 GeV Yield of 0.5 at ~115 GeV 29/10/09 Positron Workshop 6