ISR intersection I2

Towards the left one sees, on top of ISR beam 1, the front section of the 30-metre-long, small-angle spectrometer from the CERN-Holland-Lancaster-Manchester single-particle production experiment. It consists of two special septum magnets carrying up to 20 kA each. These magnets are necessary to force charged particles produced at small angles away from the ISR beam. They are followed by two threshold Cerenkov counters and (not visible) three more bending magnets and a 6-metre-long Cerenkov counter. Particle identification follows from the Cerenkov signals after determination of the particle trajectory through the spectrometer with magnetostrictive spark chambers. The positions of the first magnets and Cerenkov counters can be changed by remote control. In front one sees the electronics which determines the traversal of a charged particle from scintillator counter signals and gives the "fire" signal for the spark chambers.