This is a viewpoint on the letter by X Xu et al (2018 Supercond. Sci. Technol. 31 03LT02). The ability of a superconducting wire to tolerate thermal disturbances increases in direct proportion to its heat capacity C. In view of the recent letter by Xu et al [1] , addition of even modest amounts of materials with high heat capacity to a prototype Nb 3 Sn magnet conductor significantly improves the response of the conductor to instabilities. This success is meaningful because their key

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... n, addition of GdO 3 powder, was incorporated with a modern, high-current conductor design that can be scaled to production. The design of Xu et al extends earlier work by Keilin et al [2] for additions of PrB 6 in bronze-route wire, so other materials and design options are available. When taken together with other advances that affect the flux-pinning mechanism [3, 4], the possibility of new high-current, disturbance-tolerant conductors could extend Nb 3 Sn magnet technology toward new possibilities and higher fields. Nb 3 Sn magnet conductors have been essential for magnet technology above 10 T field for decades. The present status of production is defined by the ∼600 tons of conductors procured for ITER [5], ∼30 tons for the High-Luminosity Upgrade of the Large Hadron Collider (HL-LHC) at CERN [6], and several tons delivered annually for solenoids. Medical imaging magnets have not taken a serious bite into Nb 3 Sn production [7], which makes large science projects the present driver of conductor technology. The HL-LHC conductors [8, 9] have roots in the development period between 1995-2005, when the critical current density within the noncopper wire area J c was pushed from ∼2000 to above 3000 A mm -2 at 12 T and 4.2 K and the manufacturing cost was driven down. An additional decade was required to understand different performance trade-offs related to magnet technology and optimize production [8] . The present conductor is routinely capable of J c above 1000 A mm -2 at 16 T, 4.2 K, and, if pushed aggressively, can achieve J c close to 1400 A mm -2 at 16 T and 4.2 K [10], which is just shy of targeted needs for possible future particle accelerators [11] . HL-LHC conductors are also made with very high yield in continuous lengths, typically 2-3 km and sometimes >9 km. Yield is an important benchmark, because it affects the cost of the conductor doubly, first by increasing the price from the supplier, and second by increasing the downstream losses for cabling remnants. Research toward future accelerator magnets often defines the technical challenges at the conductor level. Since high-current density in Nb 3 Sn conductors cannot, so far, be maintained down to an effective filament diameter where magnetization instabilities can be suppressed [8] , magnets are wound with conductors that experience instabilities at low fields. These instabilities can trigger quenches of the magnet. A key factor in the decision [9] to use a conductor with 55 μm sub-elements (the conductor dimension which determines effective filament diameter) was the observation that the amplitude of flux jumps was greatly reduced when at 1.9 K [12]. Magnet tests [13] confirmed the reduction of risk. The magnetization data presented by Bordini et al in [12] is very similar to that presented by Xu et al in their letter, although Xu et al carried out their experiment at 4.2 K. Evidently, the high-C additive absorbs the energy released by local instabilities faster than the time required to expand the instability across many