Pion yield vs. geometry of target and ~20 T pulse solenoid for a muon collider experiment

The Muon Collider Collaboration is proposing a pion-capture experiment that employs BNL´s Alternating Gradient Synchrotron, a liquid metal target, and a pulse solenoid precooled by liquid nitrogen. This paper compares the yield with various target diameters, orientations and magnetic field profiles. To equalize costs, all magnets have the same mass, 12 metric tons. The magnet has two nested shells, energized sequentially. The outer set of coils, energized at 4 MVA, generates ~1/3 of the field in the target, most of the field downstream from it, and stores ~21 MJ, from which to energize the inner coil. The computer code MARS predicts that the meson yield 5 meters from the target can be ~0.35 per 16-GeV proton. This is with a mercury target of 20 mm diameter and 0.3 m length, tilted 100 mr from the field axis. The magnet field is 20 T, averaged over the target, ramping downward as (1+5z)^-1 over a 3 m length, while the bore increases inversely with the square root of the field