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A three stage magnetic bunch compression system is used to deliver electron and/or positron bunches to the FACET IP that are 17 µm (or 57 fsec) long. With 3 nC of charge per bunch this corresponds to a peak current of over 20 kAmps.
The bunches are initially compressed to 1.5 mm as they transit from the damping ring to sector 2 of the main linac at an energy of 1.2 GeV. The North Damping Ring is for electrons and is fully re-commissioned. The South Damping ring is for positrons and is due to be re-commissioned in 2012.
From sector 2 to 10 the bunches are accelerated to a mean energy of 9 GeV.
In 2002, a magnetic chicane was added to sector 10 of the main linac to compress electron bunches to 50 µm. The beam is accelerated to the chicane in such a way that when it arrives, the particles in the head of the bunch have a lower energy than those in the back. When the particles travel through the curved trajectories of the chicane, the high energy particles take a shorter path and catch up to particles in the head, compressing the bunch. Since magnets deflect electrons and positrons in opposite directions, FACET will upgrade the chicane in early 2012 by adding additional magnets, providing compressed positron bunches for the first time.
The final kilometer of linac boosts the beam to a mean energy of 23 GeV.
A new magnetic chicane was installed at Sector 20 in 2011. The SLAC linac electron or positron beam can be compressed in length to sizes appropriate for plasma wakefield accelerator research.
SLAC National Accelerator Laboratory, Menlo Park, CA
Operated by Stanford University for the U.S. Dept. of Energy