Al-Ti-MgB 2 conductor for superconducting space magnets Riccardo Musenich, Valerio Calvelli (INFN Genoa) Davide Nardelli, Silvia Brisigotti, Davide Pietranera, Matteo Tropeano, Andrea Tumino, Valeria Cubeda, Giovanni Grasso (Columbus Superconductors Genoa) The study co-funded by the INFN CSN5 (SR2S-RD) and by the EU FP7 SR2S Project
shielding strategies active electrostatic plasma passive based on the ionization losses in materials of sufficiently depth to stop the incident particles magnetostatic large superconducting magnets surrounding the spacecraft cabin
magnetostatic shielding large turns solenoids toroids
Toroid surrounding the spacecraft Compact Confined field But...
it needs a strong inner mechanical structure R i = 2.4 m R e = 6.3 m Bdr 8 T m 25 bar on the inner structure large mass
Lighter structure Non-axial, toroidal configuration
J c =80 A/mm 2, limited by the energy density Volume of the conductor 9 m 3 The mass of the conductor is a major issue The average mass density of the conductor must be as low as possible
Further requirement for a space-borne superconducting magnet: High stability No liquid helium
Choice of conductor Titanium clad MgB 2 tape + aluminium strip Materials densities: titanium: ρ= 4.5 g/cm 3 Aluminium: ρ= 2.7 g/cm 3 MgB 2 : ρ= 2.55 g/cm 3 Ti/MgB 2 ratio 2.7/1. 75 μm thick insulation. Total conductor cross section: 9.25 mm 2. Average mass density : 3000 kg/m 3.
Choice of conductor Comparison between cables based on YBCO (or ReBCO) CC and Ti-MgB 2 d YBCO CC = 8500 kg/m 3 d Ti MgB2 = 4000 kg/m 3 <d> [kg/m 3 ] 9000 8000 7000 average density YBCO cc + Al Ti-MgB + Al 2 6000 If I op = α I c 5000 < d >= αj overall J e d tape d Al + d Al 4000 3000 2000 The same average density is reached if J e (YBCO CC) = 4 Je(Ti MgB 2 ) Al density 2 3 4 5 6 7 8 9 10 J e /J overall
Choice of conductor Stability: Respect to NbTi conductors operating at 1.8 K, an MgB 2 conductor operating at 10 K is more stable. If the temperature margin is 1 K : AMS conductor (Al stabilized Cu/NbTi) ΔH=420 J/m 3 SR2S conductor (Al stabilized Ti/MgB 2 ) ΔH=2000 J/m 3
SR2S prototype conductor development The layout of the prototype conductor is based on a Columbus Superconductors standard Ni-MgB 2 tape. The tape can be soldered to a copper strip to protect magnets in case of quench. 3 mm 0.5 mm
The use of titanium instead of nickel required an R&D activity aimed to modify the production process (cold work and heat treatment) 500 Ic [A] 450 400 300 J e [A/mm 2 ] 350 300 200 250 200 150 100 1 1.2 1.4 1.6 1.8 2 B [T]
Once the process has been tuned, 100 m of Ti-MgB 2 tape were produced. Then, a longer batch (360 m) was produced in order to wind a small demo magnet. The modification of the process to produce a longer wire has brougth to a slight change in the dependence of the Ic versus field.
Next step was to develop a tecnique to bond an aluminium strip on the superconducting tape. Titanium and aluminum cannot be directly soldered together. They need to be pickled to remove oxides with a selected solution and plated with copper and soldering metal. It was decided to use tin as soldering metal for the prototype conductor. In order to deposit a thin layer of tin on one side, the tape was previously varnished. Al strip Ti-MgB 2 tape It was found that the soldering of aluminium strip was the most critical step of the whole process (deformation and detachment during cooling). Therefore it was decided to solder a copper strip onto the titanium surface.
360 m Ti-MgB Ti-MgB 2 tape during copper plated 2 copper plating Ti-MgB 2 tape Ti-MgB 2 tape varnished before tin plating Cu-Ti-MgB 2 tape
During the co-lamination of copper on Ti-MgB 2 tape, a partial degradation of I c occurred. Measured at INFN, Genoa. Thanks to R. Musenich.
However, we know that it is possible to obtain better conductors Several line parameters have to be changed in order reduce the mechanical and thermal stress on the conductor. Ti-MgB 2 sample extracted from trial short length.
Conclusion A titanium sheath MgB 2 tape was developed for the space radiation shield project SR2S. 360 m of Ti-MgB 2 tape were produced (and copper stabilized). The coupling of the superconducting tape with aluminum strip needs further development. The existing Ti-MgB 2 tape has been proposed for other space applications.
Information about the project: http://sr2s.eu/
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