Conceptual design of a magnet system to generate 20 T in a 0.15 m diameterbore, employing an inductor precooled by liquid nitrogen

The research program for an eventual neutrino factory or muon collider need s a magnet of similar to 0.15 m diameter bore to generate similar to 20 T o ver a length of similar to 0.3 m. Downstream for similar to 3 m the field s hould fall gradually to similar to 1.25 T, while the bore increases fourfol d inversely as the square root of the field. A conventional magnet would re quire similar to 40 MW; a superconducting or hybrid magnet might cost tens of millions of dollars. An economically feasible system employs a pulse mag net precooled by liquid nitrogen, with two sets of coils energized sequenti ally. An outer set of coils of similar to 12 tons, energized in similar to 20 s by, a 16 kA; 250 V supply available at Brookhaven National Laboratory, generates a peak field of similar to 9 T and stores similar to 20 MJ. A re sistor of similar to 1/4 Omega inserted across the terminals of the set int roduces a voltage drop, initially similar to 4 kV, to energize an inner set of coils to similar to 10 kA in similar to 1/4 s. This set adds similar to 13 T to the similar to 7 T remaining from the outer set, whose current has decayed to similar to 12 kk Complicating the design is a superconducting c oil once part of the PEP-4 detector at the Stanford Linear Accelerator Cent er, that begins only similar to 2.2 m downstream and is sensitive to eddy-c urrent Beating by rapid flux changes. Therefore the proposed magnet system includes a conventional de coil of similar to 0.7 MW to distance the pulse magnet from the PEP-4 colt Also, a bucking coil in series with the outer se t reduces by an order of magnitude the pulsed flux seen by the PEP-4 colt T he bucking coil serves also to reduce the axial force on the PEP-4 cryostat to below its limit of 200 kN.