Results from the Final Focus Test Beam” The Final Focus Test Beam Collaboration[l]

First experimental results from the Final Focus Test Beam (FFTB) are given in this report. The FFTB has been constructed as a prototype for the final focus system of a future TeV-scale electron-positron linear collider. The vertical dimension of the 47 GeV electron beam from the SLAC linac has been reduced at the focal point of the FFTB by a demagnification of 320 to a beam height of approximately 70 nanometers. One of the challenges to the development of TeV-scale e+e- linear colliders is to make particle beams with extremely small sizes. Whereas the bunches in the SLC are millimeter-long needles a micron across, those in future machines will need to be ten times shorter and up to a hundred times narrower. Producing and colliding tightly focused beams requires careful control and stabilization of magnetic elements, and places considerable emphasis on accurate measurement of the properties of the beam itself. We have completed construction of a prototype focussing system for a future linear collider. This Final Focus Test Beam (FFTB) [2]---which occupies 200 meters in the straight-ahead channel at the end of the SLAC linac (Fig. 1)---is designed to accept the SLC electron beam as input and to produce a focal point at which the beam height is demagnified by a factor of 380, to a size smaller than 100 nanometers. Similar compression factors will be required for the final focus of TeV-scale linear colliders. The SLC damping ring can produce an invariant emittance of yEy = 7 X 10-7 rad*m, and the results presented here were obtained with 0.65 x 1010 electrons per pulse transported to the end of the linac with a vertical emittance of typically 2 x 10m6 rad*m. The nominal beam energy was 46.6 GeV, and the spread in particle energies was maintained at + 0.05- 0.1%. The optics of the FFTB [3] are corrected to third order for geometric and chromatic aberrations, and are designed to reduce this beam to a spot with vertical height of 52 nm. SL