Choose timezone
Your profile timezone:
Powered by Indico
v3.3.3-pre
Please note that the we kindly ask you when connecting to this seminar to mute your microphones and cameras in order to have a good connection.
Abstract:
Since Nb3Sn first became commercially available in the 1960’s, non-Cu Jc values have steadily climbed until a plateau was reached at about 3,000 A/mm2 (12 T, 4.2 K) in the early 2000’s. Comprehensive analysis of recent wires suggests that the two primary manufacturing methods; Powder In Tube (PIT) and Rod Restack Process (RRP) have yet to achieve their maximum potential as high Jc conductors. Currently, PIT wires obtain a maximum Jc (12 T, 4.2 K) of about 2700 A/mm2 and do so by converting up to 60% of the non-Cu cross section into superconducting Nb3Sn. However, about a quarter of this Nb3Sn is made of large grains which are too large or otherwise disconnected to carry current in transport. The most recent RRP wires typically achieve Jc (12 T, 4.2 K) values of around 3000 A/mm2 by also converting about 60% of the non-Cu cross section into A15, however nearly all of that has the desired small grain morphology with high vortex pinning, ideal for current transport.
The demands of an FCC requires higher Jc Nb3Sn, which will also operate at higher fields in the 16 T range. To achieve a new specification of 1500 A/mm2 (16 T, 4.2 K) it is necessary to push the existing wire designs to their limits, while simultaneously considering new wire designs that could achieve higher Jc by improving vortex pinning. For RRP, a wire with the Jc (12 T) of 3,000 A/mm2 would have a Jc (16 T) of ~1100 A/mm2. New developments in heat treatment optimization of these existing wires have now driven that Jc (16 T) up to ~1300 A/mm2, also with a 2 T increase in irreversibility field (Hirr). For PIT type wires, substantial work went into designing an oxide-route where the powders and alloys were changed such that small, ZrO2 particles would precipitate in-situ and form additional pinning centers. This work was successful in proving the principle previously shown through irradiation damage of the conductor; point pinning through defects can lead to very high layer Jc. However, there were some concerns about low Hirr, drawability of the wires, and also long heat treatment schedules so a search began in parallel for oxide free routes. Most recently, there was substantial progress at the Applied Superconductivity Center in the development of a non-oxide route to form high Jc Nb3Sn by including a small amount of Hf in the commercially available Nb4at%Ta alloy which prevents recrystallization up to 750°C; ideal for nucleating small grained A15 phase of Nb3Sn. These wires show even higher layer Jc’s than the ZrO2 formulation, retain a high Hirr, and have already been made into meter length, multifilament conductors.
In this seminar, we explore the detailed characterization methods and most recent results of these modern Nb3Sn wires both at the Applied Superconductivity Center and now in the SCD section of CERN where, in the past two years, the lab has seen a substantial reinforcement of technical facilities for such analysis.
VIDYO room : https://vidyoportal.cern.ch/join/4JiI2jRNys