The Final Focus Test Beam (FFTB) facility was built in 1993 by an international collaboration and includes magnets and other beam elements constructed in Russia, Japan, and Germany, as well as the United States. Its purpose is to investigate the factors which limit the size and stability of the beam at the collision point for a linear collider. Since the rate of collisions depends on beam density, the ability to focus the beam to a tiny size at the collision is one of the critical parameters that will determine the research capability of such a facility.
The FFTB facility is a straight-ahead extension of the SLC linear accelerator. It uses a series of magnetic elements to reduce the size of the beam produced by the linac. The design goal is to achieve beams with a cross-section size of 1 micron horizontally and 0.06 microns vertically. In addition, it will investigate precision methods to detect such tiny beams and the limitations on stability in the location of the beam at the focal point.
In 1994 the FFTB achieved the beam spots with height 0.07 microns, the smallest ever recorded to that time and close to the design goal. Studies on ways to improve the reproducibility and stability as well as to further reduce the beam size are ongoing.