Peter McIntyre Texas A

1
Nb3Sn Conductor Development Impact on
Mesostability

• Sharmili Datta and Xuekui Fu
• Accelerator Technology Corp.
• Peter McIntyre and Akhdiyor Sattarov
• Texas AM University

2
Conductor Development Program Goals

• Jc 3 kA/mm2 _at_ 12 T 4.2 K
• Deff lt 40 ?m
• Theat lt 200 hr
• Strain tolerance
• 10 km piece length
• Cost lt 1.50/kAm
• Microstability/mesostability?

3
ATC is developing manufacturing technology for
reacted-rod internal-tin conductor batch
process ?continuous process

• Large hollow subelement billet
• No gun drilling
• 400 kg billet x10 fewer batches, less handling
• Insert Sn core after extrusion
• Phase 1 SBIR, completed 2004
• Extrude subelements to cm diameter
• Continuous Tube Forming Ta barrier, Cu
  stabilizer
• Minimize cold work of Ta no cracking
• Ta barriers on all subelements no bridging
• Continuous process no piece length limit
• Phase 1 SBIR, completed 2003
• Integrate hollow-billet ? CTF Ta, Cu ? Continuous
  restack ? 400 kg batch
• Phase 2 SBIR proposal, under review

4
Mesostability

• Near jc, current and heat must distribute from
  one subelement to another.
• Current and heat from an internal subelement must
  pass through either adjacent subelements or
  inter-subelement Cu
• Most IT conductor uses Nb or Nb/Ta barriers on
  subelements, not Ta. Inter-subelement copper
  tends to be bronzed during reaction, high
  resistivity

5
Inter-subelement copper plays an important role
in mesostability

• Every subelement has intact Ta barrier
• Cu layer between subelements should have good RRR

Wiedermann-Franz Law High electrical
conductivity ? High thermal conductivity
6
High-conductivity copper between subelements is
magic for mesostability against a quench within
one subelement

• Transport current to re-distribute to neighboring
  subelements
• Transport heat to heal the microquench
• Need to develop valid model to optimize amount,
  distribution of copper

7
Continuous Tube Forming for applying Ta barrier,
Cu stabilizer
8
RD improve Ta barrier

• ATC is developing powder metallurgy, bonding
  technology to prepare finer-grain Ta foils and
  bond them directly to Cu sheath foil prior to CTF
  application
• Decrease Ta grain size 20 ?m ? 2 ?m
• Bi-laminar Ta/Cu foil

9
How not to prepare a billet!
10
We want to develop a model for mesoquench
stability we need help!
11
Hollow billet development

• Two goals
• Smooth surface on copper ID
• IGC performed a hollow extrusion 15 years ago,
  but abandoned it because of folding/striation
• Preservation of registration of Nb elements
• 150 kg billet prepared and extruded success and
  failure
• Copper ID completely smooth and unfolded
• Polish inner mandrel, hone billet ID
• Registration destroyed
• NbTi rods were not annealed, did not extrude.
• Could have been cured by simple anneal
  stupidity!