Superconducting MgB2 Tubes for Passive Magnetic Field Shielding for Electron Ion Collider

Design of proposed future Electron-Ion Colliders (EIC) calls for an interaction region comprised of high field quadrupole for the heavier proton beams and an almost field free path for the electron beams. Magnets in the interaction regions have great challenges due to tight space and beam-beam interactions. A passive magnetic shield would reduce the spatial requirements around the electron beam pipe, lower the current in the required high field quadrupole, and possibly increase the luminosity. A superconducting solution is very promising for magnetic shielding since non-superconducting materials have limited capability at very low temperatures due to the loss of permeability. While low temperature superconducting NbTi wire commonly used in active shielding windings in MRI and NMR systems could be a choice in the future EIC, passive shielding in superconductor tubes will be much more compact than powered shielding with superconducting wires. Whereas long tubes of high temperature superconductors are costly and extremely challenging to fabricate, such is not the case for magnesium diboride (MgB2), a superconductor with a critical temperature of 39 K. MgB2 is proposed as a shielding material not only because it provides the possibility to safely work at intermediate temperatures (20–30 K) or operate in the boil-off of liquid helium already present in accelerator magnet systems, it also has many other advantages: 1) Higher temperature margin would reduce the need for NbTi shielding; 2) Shielding is passive and therefore would not require a power supply; 3) Shield tubes can be manufactured by a pressureless sintering technique to produce large parts in various shapes, including cylinders that can be designed to trap or hold transverse fields in the detector; 4) Low fabrication costs; 5) Radiation tolerant. We are proposing approaches aimed at realizing the potential of MgB2 for magnetic shielding in accelerator and magnet systems, focusing on manufacturability and utility: 1) conduct computer modeling/simulation to develop preliminary shield tube designs and specifications based on MgB2 superconductors; 2) fabricate prototype MgB2 cylinders based on BNL shield designs employing two different processing approaches and validate superconductivity properties with microstructural, material, electrical and magnetic evaluations; 3) fabricate sub-scale MgB2 cylinder for evaluation at BNL. In addition to utility in accelerator and magnet systems, other commercial applications of MgB2 bulks include magnetic levitation; magnetic bearings for flywheels, contactless cryogenics suspension systems, vibration isolation, reaction wheels, thermal disconnect, extended life bearings and feed-through power transmissions; inductive superconducting fault current limiters; motors and generators, including stator and rotor coils for 5 to 20 MW large direct drive wind turbine generators; and separation magnets.