15 Th November 2006 CARE06 1 Nb 3 Sn conductor development in Europe for high field accelerator magnets L. Oberli Thierry Boutboul, Christian Scheuerlein, Jean-Louis Servais, Zinur Charifoulline, Daniel Leroy, Arnaud Devred

15 Th November 2006 CARE06 2 OUTLINE Introduction NED Conductor Specification Conductor development plan Status of strand development Conclusion

15 Th November 2006 CARE06 3 INTRODUCTION MOTIVATION To promote the development of high performance Nb 3 Sn wires and cables in collaboration with European industry To get ready in Europe for the next generation of accelerator magnets GOAL To develop a conductor for high-field dipoles and high-field gradient quadrupoles needed for LHC luminosity upgrade in the Insertion Regions. In the frame of the CARE (Coordinated Accelerator Research in Europe) project, the NED activity has started with a preliminary design of a large aperture, high field Nb 3 Sn dipole aimed at deriving meaningful Nb 3 Sn conductor specification.

15 Th November 2006 CARE06 4 NED strand specification Diameter1.250 mm Effective filament  m Cu to non-Cu ratio 1.25 ± 0.10 Minimum critical current 818 A at 15 T & 4.2 K non-Cu Jc at 4.2 K1500 A/mm 2 at 15 T 3000 A/mm 2 at 12 T 2   M< 300 mT at 2 T & 4.2 K RRR (after heat treatment)> 200 a large number of filaments =>=> The main NED strand characteristics are: The main cable characteristics are: Trapezoidal Rutherford cable with a width of 26 mm 40 strands Minimum critical current A at 15 T & 4.2 K

15 Th November 2006 CARE06 5 Why NED strand is innovative ? NED strand of 1.25 mm 288 Nb 3 Sn filaments 50  m filament diameter OST strand of 0.7 mm 54 Nb 3 Sn filaments considered as the State of the Art with 3000 A/mm 2 at 12 T & 4.2 K ~ 80  m filament diameter

15 Th November 2006 CARE06 6 Why filament diameter is important ? Magnetization curves of OST strand with ~ 80  m filament diameter Flux jump in the range of 10 mT which can give a  b 3 ~ 2 units at B inj = 1T - 1. To limit field distortions in accelerator magnets: induce multipoles errors are indeed proportional to the magnetization and are especially significant at low field. M  J c d eff 2. To limit flux jumps to achieve good quench performances: large filament diameter produces flux jumps which are more likely to occur at low fields where Jc is the larger. Flux jumps are accompanied by power dissipation which can lead to a quench.

15 Th November 2006 CARE06 7 Conductor Development Strategy Based on the NED specification, a call for tender was issued by CERN 2 contracts were awarded late September 2004 in the frame of the NED/CARE project to : 1.ShapeMetal Innovation (SMI) for the production of 290 m of cable by the Powder In Tube (PIT) technology. 2.Alstom Magnet and Superconductors for the production of 580 m of cable by the Internal Tin Diffusion (ITD) technology. The goal is to develop both technologies with the objective to have an industrial process suitable for large-scale applications.

15 Th November 2006 CARE06 8 Conductor Development Plan A development plan was established with each company to reach step by step the NED goals (1636 A at 12 T & 4.2 K in a strand of 1.25 mm with 50  m effective filament diameter). The potentiality of the billet design and the manufacturing process were discussed with each company in view of its industrialization Step1 : Qualification of initial strand design Fabrication and test of at least 10 kg of strand Step2 : Qualification of final strand design Fabrication and test of at least 10 kg of strand and relevant cabling tests to demonstrate that the strand does not degrade at cabling Total strand and cable production

15 Th November 2006 CARE06 9 SMI : Status of strand development B 207 As part of step 1, SMI started a development based on an existing 1 mm diameter strand having 192 filaments that achieved a Jc non-Cu value larger than 2280 A/mm 2 at 12 T and 4.2 K with the target to achieve 2500 A/mm 2. For a given PIT strand layout, an increase of the Jc calls for reacting more fully the Nb tubes, which request a higher Sn content in the powder (mixture Sn + NbSn 2 ) or which calls for the use of a Ta Barrier around the Nb tubes to prevent from Sn leakage. Un-reacted Nb Nb 3 Sn Powder after reaction

15 Th November 2006 CARE06 10 SMI - Step 1 B 207 Based on the existing layout with 192 (NbTa) 3 Sn filaments, SMI produced four 3 kg billets: - 2 billets with Ta tubes - 2 billets with an increased Sn powder composition  1.00 mm, 192 filaments of  50  m Cu/non-Cu = 0.93, Sn leak due to a too high free Sn content in the powder a relatively low non-Cu Jc achieved Good behavior under deformation  1.00 mm, 192 filaments of  50  m Cu/non-Cu = 0.73, Ic = 1105 A at 12T with 84 h at 675 C Jc non-Cu = 2410 A/mm 2 at 12 T B179B201 => too many breakages

15 Th November 2006 CARE06 11 SMI : Strand deformation by rolling B201B179 def =25 % t To evaluate if the strands are capable to sustain cabling, the strands were deformed by rolling to investigate the filament layout behaviour under different level of deformation. The deformation by rolling is intended for selecting the strand design most suitable for cabling.

15 Th November 2006 CARE06 12 SMI : Strand deformation by rolling B 201 B 179 Deformation of 25 %, i.e. d 0 - t = 0.25 mm. First result: Distribution of Cu within the strand important in order the strand could sustained heavy mechanical deformation as in cabling.

15 Th November 2006 CARE06 13 SMI - Step 2 Based on the results obtained in Step 1, the decision was taken to continue the development with a strand design for NED.  A strand of 1.25 mm in diameter with 288 (NbTa) 3 Sn filaments to get 50  m filament diameter,  Keeping the same NbTa tube and same powder composition as for billet 179,  By adjusting the filament layout to have more copper around the filaments. B 207 B201B215

15 Th November 2006 CARE06 14 SMI - Step 2 : Strand characterization Diameter: mm Cu to non-Cu ratio = Ic ≈ 1400 A at 12 T & 4.2 K Jc ≈ 2500 A/mm 2 RRR = 113 HT = 84 hours at C For step 2, SMI has produced a 10 kg billet (B215) drawn without breakage to 1.25 mm in diameter (strand of ~ 900 m). The critical current density goal of 2500 A/mm 2 at 4.2 K and 12 T has been achieved in a strand with 50  m filament diameter.

15 Th November 2006 CARE06 15 SMI – Deformation by rolling on B215 Samples from B215 were rolled at different levels of deformation Def = 28 % The samples deformed at a level of 28 % sustained well the mechanical deformation. The SMI-NED strand has passed successfully all the deformation tests and has to be qualified by cabling test.

15 Th November 2006 CARE06 16 ALSTOM : Status of Strand development The manufacturing process of Alstom is based on the Internal Tin Diffusion technology. Technological goals for step 1 were : Develop the ITD process based on a double stacking billet design and on cold drawing Optimize sub-element composition to have the highest possible Nb fraction and to provide enough Sn to react part of the Nb barrier and to be at the stoichiometry Optimize strand design to get a good workability. Sn core Nb barrier Nb filament Sub-element with the Sn core

15 Th November 2006 CARE06 17 ALSTOM : Status of Strand development A billet assembled with 78 sub-elements was drawn to 1.25 mm with only few breakages. => effective sub-element diameter of 85  m. Part of the billet was drawn to 0.8 mm to reach 50  m for the sub-element diameter. Drawing done successfully with only one breakage. All these results indicate that a good design has been achieved for the sub-element. During step 1, Alstom tried few sub-element designs with different filament layouts. Only one sub-element design was qualified for its excellent workability.

15 Th November 2006 CARE06 18 ALSTOM : Status of Strand development Diameter: 1.25 mm Sub-elements: 78 (~ 85  m) Cu to non-Cu ratio = 1.54 Ic ≈ 740 A at 12 T & 4.2 K Jc ≈ 1500 A/mm 2 RRR = 100 HT = 120 hours at C The first Alstom/NED wire was characterized by Alstom/MSA and CERN. The critical current density achieved for the wire corresponds to the calculated value, as for this sub-element, there was a large amount of copper within the sub-element.

15 Th November 2006 CARE06 19 ALSTOM : Status of Strand development Alstom is now focusing the development on the manufacturing process of the final billet to switch from 78 to 246 sub-elements in order to get 50  m sub-element diameter. A sound sub-element design has been achieved by Alstom during step 1. The sub-element design is being used for step 2 keeping a very similar filament layout but increasing the amount of Nb and decreasing the amount of Cu which should gives at least a non-Cu Jc of 2500 A/mm 2 at 12 T. For step 2, Alstom has launched in fabrication few billets with mainly 2 different sub-element designs.

15 Th November 2006 CARE06 20 Conclusion Significant progresses have been achieved by the NED program. SMI has developed a superconducting strand made of 288 Nb 3 Sn filaments which achieved 2500 A/mm 2 at 12 T and 4.2 K. Vigorous effort were carried out by Alstom to develop the NED strand and very encouraging results have been obtained. The Jc was already doubled as compared to the value achieved by Alstom before starting the NED program and a sound sub-element design has been obtained.