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A conceptual design is presented for the 50 Tesla superconducting solenoids that are required for an optimized fast cooling ring in current designs for multi-TeV muon colliders. The solenoid utilizes high-performance multifilament Bi-2212/Ag round strand.The conductor is a cable-in-conduit consisting of six such strands cabled around a thin-wall spring tube then drawn within an outer sheath. The spring tube and the sheath are made from high-strength superalloy Inconel. The solenoid coil comprises 5 concentric shells supported independently in the conventional manner. Each shell consists of a winding of the structured cable, impregnated in the voids between cables but empty inside so that the spring tubes decouple stress so that it cannot straindegrade the fragile strands, and a high-E stress shell.An expansion bladder is located between the winding and the stress shell. It is pressurized and then frozen to provide hydraulic compressive preload to each shell. These provisions makes it possible to accommodate ~10 T field contribution from each shell without degradation, and to distribute refrigeration so that heat is removed throughout the volume of the windings.

The block coil geometry utilized in recent high-field dipole development has significant benefit for applications requiring rapid cycling, since it intrinsically suppresses coupling currents between strands. A conceptual design for a 6 Tesla dipole has been studied for such applications, in which the intra-strand losses are minimized by using bronze-process Nb 3 Sn superconducting wire developed for ITER. That conductor provides isolated fine filaments and optimum matrix resistance between filaments. The block-coil geometry further accommodates placement of He cooling channels inside the coil, so that heat from radiation and from AC losses can be removed with minimum temperature rise in the coil. The design could be operated with supercritical helium cooling, and should make it possible to operate with a continuous ramp rate of 5-10 T/s.

Virtual impactor fractionation has been used to remove all particles over a selectable micron-sized threshold in samples of precursor powders for MgB 2 and Nb 3 Sn superconductors. In a virtual impactor the powder is dispersed in an aerosol stream and passed through a vane geometry in which particles less than a critical size follow the gas streamlines which turn abruptly into a collection chamber, while particles larger than the critical size pass undeflected into a reject chamber. The aerosol dispersion was made in an inert gas flow in order to prevent degradation of the powder by exposure to oxygen or moisture.