Proposal for A Multi-Use Test Beam in the SLAC B-Line

With the impending construction of the Linac Coherent Light Source (LCLS) [1] at SLAC, displacing the well-used Final Focus Test Beam (FFTB) area, there is growing interest in developing a new test beam facility which makes use of the remaining 2/3 of the SLAC linac, and is available during LCLS operations. The success of the Sub-Picosecond Pulse Source (SPPS) [2] and the desire to preserve this capacity suggest a new beamline with similar or improved electron beam quality, including bunch length compression to 10 μm. Beam availability during LCLS operations requires a new 1-km bypass beamline connecting the 2/3-point of the linac with, for example, the existing B-Line tunnel at the end of the linac. A second operating mode, with LCLS not running, is then available using the existing connection directly from the end of the linac to the B-line. This path would provide the highest beam quality at 30 GeV and also allow a third operational mode by deflecting a few of the very high-brightness 120-Hz, 14-GeV LCLS bunches at low rate (1-10 Hz) into the B-line. Additionally, linear collider research might also be carried out in a short final focus system at the end of the B-Line, capable of producing a 70-nm rms transverse beam size. We describe a design for these systems.