Magnesium Diboride Superconducting Strand for Accelerator and Light Source Applications

The U.S. Dept. of Energy´s goal for multifilamentary (MF) strand intended for accelerator applications includes current densities, J_c, of up to 1200 A/mm² in fields of 12-16 T. Although MgB₂ films possess B_c2s at 0 K as high as 50 T, and J_cs (self field) as high as 10⁷ A/cm² have been reported, it may be several years before the above goal is attained in round MF MgB₂ wire. But when its electrical properties become suitable MgB₂´s critical temperature of 39 K will be an added advantage in the accelerator magnets´ high radiation environment. In the meantime, some near-term applications have been identified. Continually improving properties may enable MgB₂ to be used in the windings of: (i) undulator magnet upgrades and replacements, (ii) wiggler magnets, (iii) light source bending magnet replacements, or (iv) some of the lower field solenoids of a proposed muon collider. Active research-and-development programs are yielding MgB₂ strands with some remarkable properties: critical fields B_c2 and B_irr in the ranges 28-33 T and 24-29 T, respectively, and J_c (4.2 K)s in the range 1.1-5.5times10⁵ A/cm², 5-2 T, respectively. Recent superconducting undulator (SCU) magnets are calling for J_c, B_W (winding-field), B₀ (beam-line field) combinations such as 1.1times10⁵ A/cm², 3.3 T, 1.0 T. These specifications, in the light of its existing performance levels, indicate MgB´s potential suitability for the windings of SCU´s. A model MgB₂ coil-set is described