High Current Density Nb3Sn Conductor
Future accelerator magnets need high current density at high field. Nb3Sn is the material presently best for this purpose.
Presently available Nb3Sn conductor is mostly made by "bronze method". The amount of tin in bronze is limited and the space for bronze is useless to carry current. "internal tin method"has pure tin to be reacted with niobium and the current density is higher. But still it is not sufficient.
We need improvement of Nb3Sn conductors.
However, there is not much expectation of improvement for the material itself after 40 years of development. What we can do is:
1) More superconductor in the conductor -----
Only 20% of the conductor is superconducting in the conventional wire. Actually large volume of the conductor is wasted as bronze volume that has no contribution to the current carrying capacity.
2) Uniform formation of good quality superconductor -----
Distribution of tin after reaction is not uniform. Niobium filaments at distant is not effectively used to form Nb3Sn because of insufficient of Tin.
New Configuration DT Conductor
DT method is a variation of IT (internal tin) but tin diffusion is not "internal" any more. Tin modules are distributed in the cross section.
So we call it DT(distributed tin). The niobium modules and tin modules are separated. It has a high occupation rate of superconductor and with less wasted volume. Residual bronze workes to separate superconductor modules each other. It has such structure:
Tin Diffusion Simulation
Tin comes from out side the module and diffuses into the the niobium area. The tin density evolution is seen through the finite element analysis. The ANSYS analysis result is shown as an animation movie.
click here to see the finite element animation
Actual look of the test fabricated conductor cross section is:
How does it work? Currnt density measured at 12T exceeded 2kA/mm2. Interesting fact is that DT conductor is good for both high field and low field. Usually, high temperature processed Nb3Sn has better stoickiometry thus good at high field because of higher Hc2. Low temperature processed Nb3Sn has lower Hc2 but carries more current at low field because of fine grain structure.
High field optimized internal tin conductor is blue. Low field optimized internal tin is green. Red is DT. DT process really makes it different. DT conductor is good for both high field and low field.
We are continuing the development. We hope high current density Nb3Sn will become available for evrybody.