An “NLC-Style” short bunch length compressor in the SLAC linac

Experimental tests of a “second bunch length compressor” in a linac is important for the next generation of linear colliders and for other future accelerators. These future accelerators need bunches with lengths of order 0.06-0.2 mm. At these lengths, new accelerator dynamics will be encountered. We have studied the possibility of constructing a second compressor with the present SLAC linac and have found a reasonable design. The core of this project is to reconfigure an old beamline (BL-90) at the 1000 m location in the linac to: (1) extract a 10 GeV bunch, (2) pass it through a new 96 m long transport line in which length compression is done, and (3) reinject the beam into the main linac in an available drift section. Using the resulting compressed bunch, accelerator physics tests would be performed in the remaining downstream linac with the resulting very high charge density. The bunch compression in this transport line results from the TRANSPORT element R₅₆ as determined from the optics of the transport line. Δz=R₅₆ ΔE/E. For example, if Δz=-0.5 mm, ΔE/E=0.5%, R₅₆=-0.1 m, a bunch of 5×10¹⁰ particles would have a final length (σ₇) of about 0.08 mm with a peak current of 9600 A