Experimental Facilities: Final Focus Test Beam (FFTB)

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 was to investigate the factors that 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 used a series of magnetic elements to reduce the size of the beam produced by the linac. The design goal was to achieve beams with a cross-section size of 1 micron horizontally and 0.06 microns vertically. In addition, it investigated precision methods to detect such tiny beams and the limitations on stability in the location of the beam at the focal point.

The aim of the FFTB facility was to study: Just how small the beam bunches can be made in a reliable and stable fashion. How to detect and monitor the tiny beams. "Feedback" control systems to ensure stability of these small beam bunches.

To collide two tiny beam bunches that are only a micron or so in diameter and traveling at almost the speed of light is no small feat. To do it again and again requires all components to be extremely stable and well-controlled. A truck driving by a half-mile away causes ground movement on the scale of microns. A tiny change in electric current to a magnet changes the beam shape and position by microns. All such effects must be monitored and either removed or corrected for to maintain collision conditions. The final focus test beam was an experiment to develop the techniques to achieve this level of control.

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.

The FFTB has been decommissioned and removed for future construction projects. For more information:

• Looking Back on the FFTB (April 11, 2006)
• Valuable Real Estate in the Research Yard (April 13, 2006)
• Phase Two of FFTB Removal Begins (May 2, 2006)
• Final Focus Test Beam Removal Underway (May 23, 2006)
• SABER Moves Forward (June 14, 2006)
• RIP, FFTB (June 27, 2006)