Dipole Magnet with Elliptical and Rectangular Shielding for a Muon Collider

The Division of High Energy Physics of the US Department of Energy has expressed keen interest in technologies for neutrino factories and/or muon colliders as evidenced by its prior and recent call for proposals. The dipole magnets in the ring of a muon collider should generate the highest feasible magnetic field, because the higher the field, the smaller the ring, and therefore the more numerous the muon/muon interactions before the muons decay. The magnets require shielding from the intense muon- decay radiation: electrons (that spiral inward toward the rings axis), and electron-generated synchrotron radiation (that flies tangentially away from the rings axis). Relatively little of the radiation strays much from the plane of the ring. One can shield the coils with a tungsten pipe that surrounds the muon beam. The pipe wall needs to be thick near the horizontal plane of the ring, but towards the vertical plane can be progressively thinner. A cross section that is elliptical or rectangular, rather than circular, can halve the cost of shielding, which may be tens of millions of dollars. In addition, the magnet windings can hug the beam pipe more closely and therefore be more efficient. Appropriate coil cross sections are elliptical-cosine-theta and rectangular: racetrack coils with, if necessary, ends upturned to dodge the beam pipe. One or more of its inboard coils may be Inside-Support-Free, supported magnetically rather than mechanically. This SBIR will use the radiation-simulation code MARS to design shields for collider energies of 1.5 and 3 TeV and then generate conceptual coil designs for dipoles of 10 T, 15 T and 20 Tthe latter employing high-temperature superconductors (HTS). The designs will include predictions of field quality, temperature margin, stress, strain and deformation, for adequate margins on field quality, magnet reliability and safety. Phase II proposes to: 1) Design magnets of 15 T and 20 T; 2) Consider combined-function magnets, that incorporate quadrupole gradients in the dipole, to avoid neutrino-radiation hot-spots; and 3) Fabricate a short dipole of reduced size and field. Commercial Applications and Other Benefits: This SBIR is to advance the technology for a muon- collider ring-dipole magnet with elliptical or rectangular shielding. Applications include magnetic confinement of fusion-energy plasmas, superconducting magnetic energy storage (SMES) and, perhaps, muon radiography for medical and Homeland Security applications.