Development of High Current Density Nb3Sn Conductor with Distributed Tin Configuration

Abstract

Next generation high-energy accelerators, (VLHC for example), require magnets in the range of 10 to 12T. It is necessary to use Nb 3 Sn conductor with current density over 2000 A/mm 2 @12T for these magnets. Increase of current density can be still done by the reduction of unnecessary bronze portion of the conductor and uniform synthesis of NbsSn. Through the optimization consideration using finite element analysis, we have introduced new configurations of niobium and tin. FIT (filament in Tube) and DT (Distributed Tin) method were tried and the DT method gave a very good result. The current density of DT conductor reached 2120 A/mm 2 @ 12T. The critical field of DT conductor appeared to be high even it is cured at low temperature to suppress the grain size growth.

Characteristics of Distributed Tin Nb3Sn Conductor

“…We think that the DT configuration of the high-J c wires is important for the formation of stoichiometric and fine Nb 3 Sn grains in the filaments. In the heat treatment of the DT wires, the tin in the Sn modules can diffuse into every niobium filament in the Nb modules more easily than it can in the conventional internal tin wires because the niobium filaments are thinner and the diffusion path is always kept open [4]. Therefore, the DT method might be more suitably be called the "External Tin" method if we are considering the direction of tin diffusion.…”

“…The next generation high energy accelerators, however, such as the VLHC and the Muon Collider, require high-J c magnets with field strengths in the range of 10 to 15 T. Such magnets need NbsSn conductors with a current density over 2000 A/mm 2 at 12 T and 4.2 K, so MELCO and KEK High Energy Accelerator Research Organization have started to develop wire that has a new configuration and will perform much better than the conventional internal-tin wires [4].…”

Future Accelerator Magnet Needs

“…In Japan, a method called Distributed Tin (DT) for conductor has successfully produced wires with noncopper critical current density greater than 2,100 at 12 T and 4.2 K and effective filament diameters of less than 60 microns [25]. The DT process may also more easily enable the achievement of a higher Residual Resistance Ratio (RRR).…”