1. FACET II Project – User Area Christine Clarke 26 th June 2015

2. Introduction to FACET II FACET II will use central 1/3 SLAC linac to deliver electrons to the experimenter area in Sector 20 Project CD1 is October (still very conceptual at the moment!) CD2+CD3 September 2016 for construction in 2017 Facility for Advanced Accelerator Experimental Tests 2

3. Multi-GeV Plasma Wakefield Acceleration (PWFA) - Apparatus The main purpose for FACET II will be to continue PWFA studies FACET II’s high power electron beam ionises alkali vapour or a gas and interacts with the plasma Wakefields accelerate part of the bunch 3 http://phys.org/news/2014-11-physicists- milestone-particles-plasma.html

4. 4 PWFA in alkali metal vapours Currently we use thin beryllium vacuum tight windows upstream and downstream (50 um thick) Fill with helium to ~5 Torr Heat the lithium to ~900 degrees C Cooling jackets and a wicking mechanism keep a flat top lithium vapour density

5. 5 PWFA in room temperature gases We use H2, Ar, He Up to 30 Torr is typical Currently beryllium windows form boundary for the gas

6. 6 The problems… 1.Scattering through beryllium window contributes to beam size: 25-30 micron contribution to the spot size for 50um window FACET II beam size is 10um so this is a significant growth 2.High peak current of beam is capable of destroying beryllium windows Usually multiple shots needed but single shot has been seen The peak current for FACET II is 5 times larger than the peak current we currently operate with  Therefore we have incentive to use differential pumping. Normal window Leaky window due to beam burn-thru

7. 7 The sector Sector 20 does not include accelerating structures but it does include an x-band deflective cavity at z = 1968.57 m Vacuum requirement for TCAV is ~10^-8 Torr (needs to be verified) “Gas section” is in the area we call IP Area between z = 1991.66 m and z = 1996.88 m No vacuum requirement for after the gas section Usually aim for 10^-6 Torr compatibility in user area (we have lots of motors, cabling, laser optics etc)

8. 8 The happy FACET team