Conceptual Design of Pion-Capture Magnets of up to 15 cm Bore and 20 T Peak Field

摘要

For the Neutrino Factory and Muon Collider Collaboration, BNL has considered solenoidal magnet systems of several types to capture pions generated by bombarding a mercury jet with multi-GeV protons. The magnet systems generate up to 20 T, uniform to 5% throughout a cylindrical volume 0.15 m in diameter and 0.6 m long. Axially downstream the field ramps gradually downward by a factor of sixteen, while the bore increases fourfold. The steady-state system needed for an accelerator has many superconducting coils and a radiation resistant insert of mineral-insulated hollow conductor. Less costly, pulsed systems suffice to study pion capture and the effect of a magnetic field on a jet hit by a proton beam. BNL has explored three types of magnets, each with its principal coils precooled by liquid nitrogen. One type employs two sets of coils energized sequentially. Charged in 23 s by a power supply of 5 MVA, the 14-ton outer set generates 10 T and stores 28 MJ, from which, in 1/3 s, to charge a half-ton inner coil that adds 12%T to the 7%T remaining from the outer set. An alternative design uses 25 MVA to energize, in 1.4 s, a single 3-ton set of coils. The third type bows to budgetmy constraints and is more modest in size and performance. A magnet of 2-3 tons generates 10-11 T with only 2 MVA, in a bore big enough (11 cm) to accommodate the jet. It forgoes the field ramp that improves pion retention.