Preamble. It represents the known binary compounds showing SC at the highest temperature to date. No weak links. Possibility to incresase J c and H c2

Transcription

1 Preamble It represents the known binary compounds showing SC at the highest temperature to date. No weak links. Possibility to incresase J c and H c2 As virtually all SC s used in large scale industrial apllications today are binary LTS materials (NbTi, Nb 3 Sn), it appeared immediately evident that MgB 2 might have represented a new option with better performance in field than LTS Helium is a natural resource available in limited quantities and represent a bottleneck to industrial applications, so MgB 2 is a convenient solution thanks to high T c Cryocooler: new technology to coll superconductors Cryogenic free cooling: a key technology for a more widespread use of SC s; allow for the realization of dry superconductng devices with no need of expensive, dangerous and difficult handling and storage of cryogens

2 J c performance of SC wires

3 SC wires available on the market

4 Additional parameters

5 PIT: fabrication option I step: tube filling in-situ ex-situ B + Mg + B Mg MgB 2 II step: cold working III step: thermal treatment wire drawing wire rolling Powders compaction Reduced size and increased length Thermal treatment for Synthesis (in-situ reaction) to form MgB 2 Synthering (ex-situ) to recover the properties of MgB 2 Long length of tape

6 PIT fabrication option: in-situ Key-factors: Inert sheath for homogeneous reaction reducing Mg loss Copper-Fe/Nb protective sheaths Advantages: Low cost, high speed process, small influence of the fabrication process on the SC properties Disdvantages: need of inert sheaths, inhomogeneity over long length, difficult to make multifilamentary wires with hard materials, fragility. Final thermal treatment (in-situ reaction) occurs once the coil is made wind and react conductor (not very convenient for low cost magnet manufacturing)

7 PIT, ex-situ: effect on I c Tape performance are strictly dependent on fabrication (cold working) and final heat treatment parametes Key-factors: High powder packing density Very hard sheaths (Nickel, Iron, Steel) harder the sheath, larger J c Not sintered Effect of final thermal treatment: Tc is recovered and I c (T) improves with TT

8 PIT, ex-situ: effect on pinning Tape performance are strictly dependent on fabrication (cold working) and final heat treatment parameter A new source of pinning center is present in ex-situ tape due to cold working but at 900 C they are partly removed

9 PIT, ex-situ: effect on lattice strain In situ Neutron Diffraction Experiment at ILL, Grenoble, confirms: Lattice strain increases during cold working; Lattice strain progressively relaxes during heat treatment

10 PIT, ex-situ: effect of final heat treatment

11 PIT, ex-situ: optimal conditions Optimal conditions, in terms of mechanical deformation and final theramal treatment, are different in low and high magnetic field J c after heat treatment mainly results From the compromise between MgB 2 packing density, residual lattice strain, increase in Tc, reaction layer

12 Powder and conductor optimization 2) Commercial precursors + B Mg MgB 2 5) ball milled and/or doped MgB 2 MgB 2 (doped) 4) Home made doped boron B + Mg B 2 O 3 (doped) + dopant 1) Commercial 3) Home made boron MgB 2 MgB 2 B + Mg B 2 O 3 Conductors configuration: different shape, nuber of filaments, materials, stability consideration Tube filling Powder optimization: Effect of oxygen, ball milling, doping MgB 2 Cu Fe Ni

13 MgO at grain boundaries: TEM analysis MgB 2 grains are covered with amorphous MgO layer of ~50 Å, comparable with MgB 2 coherence length: working in oxygen cleaner conditions is mandatory!

14 Magnetic J c [A / cm 2 ] Comparison between mono-tapes done with the same procedure in air and in controlled atmosphere (Glove Box). MgO at grain boundaries: effect on J c 1.E+06 1.E+05 Jc@5K 1.E+04 Glove box Air 1.E Magnetic Field (T) The critical current density increases at low field bur shows worse magnetic field dependence. In controlled atmosphere: Better connectivity Decreasing GB pinning I c in multifilamentary tape is improved by a factor 2 At 20K, 1T J c of 2000 A/mm 2 has been reached

15 B c2 [T] r [mw cm] MgO : effect on connectivity and Hc B // tape 6 4 B tape T [K] 500 O atmosphere A f = 4% 1,2 1,0 OA IA 400 0,8 Point defect pinning Inert atmosphere A f = 15% F p /F pmax 0,6 0,4 GB pinning T [K] 0,2 0,0 T=5K 0 0,2 0,4 0,6 0,8 1 H/Hk

16 Ball milling Mechanical alloyng (to obtain an alloy starting from pure elements or different compounds Mechanical milling To change granulometry or lattice parameters Mechanical disordering to introduce disorder and obtain amorphous phases Foundamentals parameters are: type of jars, energy, time, type and diemnsion of balls, ball to powder ratio (BPR), T and atmosphere. planetary ball mill planetary movement jars

17 n.p.c. Powder optimization: effect of ball milling 2μm Milled 144h 5μm Milled 77h 5μm Not milled < d > = 440 nm < d > = 850 nm < d > = 1.4 µm < d > [ mm ]

18 J c [A/cm 2 ] 10 6 Upper Critical Field (T) T = 5K B perp ab Applied field [T] Increasing milling time improves the in field J c performance, increasing H c2. The pinning force behavior is well described by grain boundaries based pinning model, F / F Pmax suggesting that ball milling process increased the number of grain boundaries lowering the average grain size Effect of ball milling on J c (B,T) c F p = b 0.5 (1-b) 2 not milled perp not milled para milled perp milled para Temperature (K) not milled increasing milling time T = 5 K H / H * K

19 I c [A] Effect of ball milling and 0.5% C doping Critical current measurements in LHe at GHMFL T = 4.2K 2t milled with carbon 10 1 Standard m 0 H [T] Milled with carbon 10 4 A/cm 2 Milled (no anisotropy) 10 4 A/cm 2 at 4.2K and 13T

20 Wire design: different configuration Nickel + OFHC Copper Monel_Ni Material MgB 2 Copper Iron Nickel Vol % Material MgB 2 Nickel Monel Vol % J c eng = A/cm at 4.2K, 2.5T (Ic= 340 A) J c eng = A/cm 2 at 4.2K, 2.5T (I c = 520 A) Monel_Copper_Ni Cupronickel_Nb Material Vol % Measurements in progress MgB 2 Nickel Copper Monel Material MgB 2 Nb CuproNickel Vol % J c eng = A/cm 2 at 4.2K, 2.5T (I c = 530 A) I c = 250A at 20K,1.2T Expected to be a low AC loss conductor

21 Critical Current (A) Wire design: I c at 4.2K Nickel + OFHC Cu Monel + Ni Monel + Cu + Ni Tape Magnetic Field (T)

22 Thermal Conductivity (W / m K) Thermal conductivity 250 Nickel + OFHC Copper 210 W / m 20K Monel_Copper_Ni Temperature (K) Cupronickel_Nb Monel_Ni For the evaluation of the basic quench characteristics on the stabilized tape configuration see: Good transport properties Need to add stabilization material A. Stenvall, by Wire A. Korpela, in Channel R. Mikkonen technique and G. Grasso Supercond. Sci. Technol. 19 (2006) Stability considerations on multifilamentary MgB 2 tapes

23 Stress (MPa) Mechanical properties K De-chucking 296K Strain (%) Mechanical performance was investigated using Instron-type test machine at room temperature and 113 K. H. Kitaguchi, NIMS-Tsukuba (JP)

24 I c /I c (Zero External Strain) T Ic-strain relation Sample No. 1 Sample No K(Liq. He) 4T Tape Surface Soldered to SUS304 Rig External Strain (%) H. Kitaguchi, NIMS-Tsukuba (JP)

25 Bended (d c < 5 cm) SEM on bended tape

26 I c [A] Requirements for application T = 4.2K 2t milled with carbon 10 1 Standard m 0 H [T] J c > 10 4 A/cm 2 has been already demonstrated by several groups Much more progress in high fields yet to come Milled with carbon 10 4 A/cm 2 Milled (no anisotropy)

27 How to meet the future wire demand? MgB2 based conductors can be designed in a number of drastically different configuration according to customers specifications Requirements must be clearly comprehended to choose: right MgB 2 powder (low or high field) materials shape-section number of filaments Customer oriented All the wires must be produced without degradation in Km-class length

28 Texas Center for Superconductivity 1 Tesla cryogenic-free solenoid magnet MgB 2 technology demonstrators INFN-Genova 2.35 Tesla dipole magnet for particle accelerators Ansaldo Breda CRIS 1 Tesla cryogenic-free solenoid magnet ASG Superconductors Paramed Medical System Open-Sky MRI CERN LHC bus bar MgB2 cable with Ic>17 ka, 18 mm in diameter SINTEF Norway Induction heater Cesi Ricerca LNe Fault current limiter Chinese Academy of Science 1.5 Tesla cryogenic-free solenoid magnet

29 Open sky MRI Patient comfort Flexible positioning of the patient Interventional MRI possibility of interaction between the patient and the medical staff The system is cryogenic free Easy installation No cryogenic liquid refill Quench No problem of dangerous over pressure due to boiling helium inside the cryostat

30 Cryogenic free magnet The magnet consists of a U-shape ferromagnetic yoke and two MgB2 coils (one for each pole, 12 Double pancake total) Main Magnet Parameters Nominal Field 0.5 T Peak Field on the Conductor 1.3 T Nominal Current 90 A Conductor critical current 400 A Conductor price ( /kam) at 20 K, 1 T < 7 Number of Pancakes 12 Conductor Length (total) 18 Km Inductance 60 H Overall Dimensions 2x2x2.4 m Patient Available Gap 0.6 m Weight Kg

31 Aluminium billet induction heater New design with DC induction heating Objectives of ALUHEAT (FP6) are: an improving the energy efficiency; an improving of the production quality; to validate the technical and economical feasibility of the new concept by building a kw aluminium billet induction heater and test it in an industrial aluminium extrusion plant. MgB 2 based coils have been already realized and tested individually: 32 double pancakes with 550 m each, and the magnet will be operated at 20K, 1.5 T

32 LHC bus bar Design of an MgB 2 feeder system to connect groups of superconducting magnets to remote power converters 12 wires around a multi strand copper 6 x 12 wires 8 x 3 wires 7 times (b) 8 times (c) First test of the 3 ka cable successfully completed at CERN using our strands I c exceeded 11 ka at 4.5 K and self field, probably reaching the optimal target of 3 ka up to 30 K A total demand of about Km of MgB 2 strands is expected for this application during the next 3 years

33 Today MRI magnets ASG, Siemens, General Electric Tomorrow Power quality and storage Market potential FCL Fault current limiter SMES SC Magnetic energy storage High energy physics Energy Motors and generators (eolic and hydroelectric field) CERN, INFN, Enea In the next 10 years * SC will have a great impact on industrial processes in several fields Transportation High efficency industrial process Marine motors Magnet levitation train Transformer Induction heater Magnetic filtering * Energy Dept-USA, METI-Japan, Connectus-EU

34 Market potential Superconductivity company are working to extend their bussines from MRI to other applications The selection of MgB 2 will mostly depend on its $/ka m ratio compared to HTS There is a high probability that MgB 2 will reach a $/ka m ratio similar to NbTi but at 15-20K. Actually NbTi is about 2 /ka m a 4.2K, 4T and MgB 2 is 8 /ka m a 20K, 2T and refrigeration cost at 4.2K is about 10 times cost at 20K. Having available round wires, SC joints, low AC losses, etc, will make Mgb2 a winning solution for some of new applications Extend our Know-How on devices, expecially in the field of energy, and their potential market Select interesting applications and find industrial and R& D partner Improve collaboration between University and research Institution

35 Info any details on tapes or wires any kind of samples for your research activities please write me: Thank you for your attention