The FFTB at SLAC is a highly sophisticated beam line, originally constructed to focus 1-ps high intensity electron pulses to sub-micron transverse dimensions, as required for the Next Linear (e+e-) Collider. To achieve that goal, the alignment of beam-line elements is very precise, and a detailed understanding of the beam-line optics exist.
The FFTB provides an ideal environment for calorimeter tests. A secondary electron beam is produced upstream of a small-angle bending magnet prior to the FFTB. Slits mounted before and after the magnet can be positioned to sub-millimeter accuracy in both position and width. The beam energy spread in the FFTB is ~0.1% and the emittance and secondary beam intensity is defined by the opening of the slits at the analysis magnet. Typical beam intensities used for T-438 averaged ~1.5 electrons per SLAC pulse. This resulted in single pulses having either 0,1,2 or more energetic electrons. All of the electrons within a single SLAC pulse arrived within ~1 ps. The repetition rate was 10 Hz.
For T-438, secondary electron beams having energies of 5, 10 and 20 GeV were tuned. The 10- and 20-GeV runs were conducted in two modes. In the focused mode, a few millimeter diameter beam was directed onto the target. In the defocused mode, the sophisticated optics of the FFTB enabled the beam to be dispersed across a ~1 cm diameter spot, providing an ideal test of the response of the shower-maximum detector.
L.C. Bland (IUCF), for the T-438 collaboration
Last revised: 31 October 1999