Measurement of the Magnetic Median Surface of the Princeton-Pennsylvania Accelerator

A description is made of the equipment used to determine the position and shape of the magnetic median surface (m.m.s.) of the P. P. A. weak focusing magnets far from the magnet ends. The reproducibility of the relative profiles of the m.m.s. was ±0.020 in. or better. The absolute location of the m.m.s. was uncertain to ±0.1 in. The effects of current sheets through the pole piece face windings and current loops on the front spacer as well as the profile of the m.m.s. were measured for many values of B(r, t), from B minimum to B maximum.