Split Field magnet at the I4 ISR intersection

The Split-Field Magnet (SFM) at I4 had an unconventional topology, consisting of two dipole magnets of opposite polarity. It formed the heart of the first general facility at the ISR. It had a useful magnetic field volume of 28 m3 and a field in the median plane of 1.14 T. With a gap height of 1.1 m and length of 10.5 m, the magnet weighed about 1000 t. The SFM spectrometer featured the first large-scale application of MWPCs (about 70,000 wires), which filled the main magnet, visible here in 1974, and the two large compensator magnets.