A view of the T-438 set up in the Final Focus Test Beam (FFTB) at SLAC.
The equipment is in nearly final form.
The beam is delivered from the right in the picture. Immediately after the orange quadrupole magnet, a 25 micron stainless steel exit window is mounted on the flange. The exit window separates the FFTB vacuum system from air. Downstream of the exit window is trigger counter A. Approximately 40 cm downstream of that counter is trigger counter B. The electronics demands a coincidence between A and B to trigger the readout of the prototype calorimeter and shower-maximum detector. Immediately downstream of trigger counter B is a counter (C) with a 2.54 cm diameter hole, aligned with the beam. The absence of a signal from counter C was used in offline analysis to distinguish electrons that shower upstream of the calorimeter.