MgB 2 ten years after: present state and perspectives for superconducting wires

1. MgB2 ten years after:present state and perspectives for superconducting wires Giovanni Grasso July 5th, 2011

2. Columbus Superconductors SpA • Established in 2003 as a start-up of CNR/INFM with minro industrial participation from ASG Superconductors aiming at the development of MgB2 products 2003 2006 Once a targeted R&D result achieved Columbus Superconductors srl Columbus Superconductors spa 1st superconducting wire in MgB2 longer than 1 Km Industrial shareholders take the Company control in order to sustain investments and plant development 75% CNR+Researchers 25% ASG

3. In January 2001 superconductivity at 40K in MgB2 was unexpectedly announced I invested about 200 € from my own pocket to buy 100 grams of MgB2 powders online from Alfa-Aesar the night after the day I knew..

4. Doesitmakeanysensetodevelopwireslooking at the basic MgB2properties? High enough for 20K operation High enough to reduce weak links Nanoparticles are propedeutic for high jc(B) High enough to produce useful fields Basic parameters are interesting enough to try making wires with an easily scalable process.. but properties are NOT exceeding LTS at 4.2 K nor HTS at 10 K+ Is there a real good reason to develop MgB2 then?

5. The LTS lessontellsthat1.Cost / 2.Strength / 3.Performance oftencounts in this ranking when the selection of a superconductingwireis made (NbTi market share typicallyoverwhelms Nb3Sn)WhileHTSmayallow for some applications at LN2 temperature, in most of the casesthey are forced to operation in the 20-50 Krangebecause of the insufficientbehavior in a magneticfield -> the comparisonbetween HTS and MgB2 can be mostlydone on a similarcooling penalty basisthanLTS 1.Cost / 2.Strength / 3.Performance

6. reaction at 900°C in Ar MgB2 Production intoWires Ex-situ PIT process Columbus plant in Genoa Chemical phase Metallurgical phase + B Mg Manufacturing of MgB2wires + bysimpleex-situPowder-In-Tubemethod Has its own production facilities in Genoa with leading capability to produce and supply MgB2 wires on a commercial basis since three years – mostly used for MRI so far MgB2 More flexibility on wire design thanHTS • The present plant is fully operational for MgB2wire production with a throughput of 2 Km/day, and is under scaling up to 3’000 Km/year according to our new market forecast with an investment > 5M€ • Wire unit length today up to 4 Km in a single piece, easily scalable by increasing billet size/length • Total plant area 3’400 m2 – 60% of it in use today, to be increased by further 1’000 m2becoming available by end of 2011 • Production for MRI so far exceeded 700 Km of fully tested wires • MgB2 compound production now also fully implemented • Increased interest from developing power applications

7. + MgB2 B Mg Commercial MgB2 High energy ball milling wire drawing to 2 mm cold rolling tube filling Flash sinteringat 900-1000°C in Ar MgB2 P.I.T. ex-situ method Possible routes: Commercial precursors Doped boron B Mg MgB2 MgB2(doped) B(doped) Mg dopant B + + + Home made boron MgB2 B Mg B2O3 +

8. Will MgB2 become soon a material for production of very high magnetic fields? • Initial results of very high Hc2 were really promising • Best results easily achieved in thin films though • Grain boundary pinning, nanoprecipitates flux pinning, structural disorder and low-temperature synthesis are the combined reasons to achieve best results

9. Requirements for applications Cost vs. performance targeted figures Theremight be some room for 10-12 Tesla magnetsifmechanicalpropertiesexceed Nb3Sn onesappreciably Realpotentialisforcryogenic-freemagnets up to 3-6 Tesla – enoughfor MRI and perhaps SMES energystorage Criticalcurrent density largerthan 100 A/mm2 at fields >> 10T alreadydemonstrated Significantresultsachieved at 20K aswell, whileoptimalproperties in high magneticfieldhavebeenachieved at 12 K High field performance demonstrated in MgB2 R&D wires by many groupsMuch more progress yet to come

10. Even MgB2as HTS mayneed some degreeoftexturingtoachievemaximum performance i.e. jc > 100’000 A/mm2 MgB2thinfilms Connectivityas low as5%asextracted from Rowellanalysis of electricalresistivitycannotexplainsystematicallylow jcvalues in the best bulk and wirematerials - lack of texturereducessuperconductingcouplingcapabilitybecause of the 2-band nature of superconductivity in MgB2 An improvement by atleast an order of magnitudeisstillfeasible by focusing on microstructureoptimization

11. Solutions for DC conductors • Rectangular and round wires are preferrable with respect to flattapesbecause of easiermagnetwindingtechnology • Large magnetsmayrequiresignificantcopperfraction in order to protectthem in case of a rapiddischarge/quench • Monolithic ex-situ wires are hardlycompatible with large copperfractionsbecause of lack of MgB2density and strong chemicalreactivity with it

12. Solutions for DC conductors 20-37% MgB2 10-16% MgB2 15-22% MgB2 20-25% MgB2 Copperabsent -> highestjcs 2*105 A/cm2at 20K 1 T, 105 A/cm2at 2 T Central Copper core -> jcsreduced by 10-20% Coppersurrouding the filaments -> jcsreduced by 30% Coppersurrouding the conductor -> jcsreduced by 66%

13. Increase Cu stabilizationwithoutdecreasingjcssignificantly The typicalwiresinteringabove 850°C brings RRR of OFHC to a valueaslowas 40 Application of a copperfraction once the wires are fullyreactedshould help in making the conductors more flexible and comparablylowercost to be manufactured Wire-in-channel and sandwich conductors are under advanceddevelopment Copperelectrodeposition and sprayingmay be alternative routes for improvingconductorcopperfraction

14. AC-lossissues with MgB2conductors • Use non-magneticmatrices • Reduce filamentsize • Increasefilamentdecoupling • Reduce wireaspect ratio near to 1:1 • Reduce reactionlayersurrounding MgB2filaments • Reduce twist pitchlength

15. Towards a low AC lossconductorarchitecture Increasefilamentcount with f.f. > 15% in order to bringfilamentsize down to 10-20 micron Ni Fe Ti MgB2Ni2.5 Nb Ni Nb-Ni Ni Iron, Niobium and Titanium are muchlessreactivethan Nickel with MgB2 Because of magneticreasons, Titanium and Niobium are ourmaterials of choice for the sheath of low-Aclosswires

16. Towards a low AC lossconductorarchitecture Wiretwisting down to 60 mm do notaffect the transportpropertiesdramatically Combining high filamentcount, Titaniumsheath, and strong twisting in a round wireshouldresult in a verylow-AC lossconductor Furtherscaling up with the filamtncountwillbecomeavailablewhenlargerinitialbilletswill be implemented

17. Is the MgB2wiretechnologyalreadyavailable?Veryactive MgB2devicedevelopmentisongoing Texas Center for Superconductivity 1 Tesla cryogenic-free solenoid magnet Brookhaven National Laboratory Cryogenic-free pancake magnet Ansaldo Breda CRIS 1 Tesla cryogenic-free solenoid magnet INFN-Genova 2.35 Tesla dipole magnet for particle physics ASG Superconductors Open-Sky MRI Some of the devicesrecentlyrealizedemployingW&R Columbus MgB2wires CERN MgB2 cable with Ic>17 kA, 6 mm in diameter Scaled up to 125 kA on a 62 mm cable SINTEF NorwayInduction heater Cesi Ricerca LNe Fault current limiter Chinese Academy of Science 1.5 Tesla cryogenic-free solenoid magnet

18. The MRI system “MR Open” First commercial systems installed in hospital in EU and North America >10 magnetsystemsproduced so far – 6 more systemswillbeshippedtocustomersworldwideby end of the year

19. DC InductionHeaterdevelopment =90% Assembly of MgB2 DC induction heater • Objectives of the project are: • to dramatically reduce energy consumption and life-cycle costs in one of the large-scale electrotechnical components with poorest energy efficiency and at the same time improve the production quality • To validate the technical and economical feasibility of the new concept by building a 200-300 kW aluminium billet induction heater and test it in an industrial aluminium extrusion plant • The magnet uses about 20 Km of MgB2 wires, and it has been successfully tested at design specs (200A, about 2 Tesla)

20. The IGNITOR nuclear fusion project Tobeinstalled in Russia withina close partnership with Italy ThisTokamakisvery compact ( about 6 m diameter), and basicallyconsistsofresistive Coppercoilscooledtocryogenictemperatures, due to the extremely high magneticfield ( >> 20 Tesla), and operated in quasi-pulsed mode. The helium gas coolingtechnologycompatiblewith the useof MgB2 The outerpoloidalfieldcoilsexperience a fieldwhichiscompatiblewithtoday’s MgB2 MgB2 cable for outer poloidal field coils Why MgB2 in this machine?To prove feasibility of future systems with muchhigher duty cycle

21. Racetrack magnetforparticleacceleratorsINFN MARIMBO project The magnet reached about 2.5 Tesla in cryogenic-free conditions Magnet was R&W with a layer by layer structure

22. 20kV distribution system DC resistive FCL design based on MgB2 A rectifier bridge and a smallinductance are usedto operate anantinductive MgB2coil in almost DC mode, reducinglosses and thereforecryogenicload Universityof Bologna development

23. Conductor manufacturing forcableapplications We are in the advanceddevelopmentphase of MgB2 round wires for cableapplications Wires are produced with differentouterdiameter of 1.1 (1 mm2) and 1.6 mm (2 mm2)

24. MgB2 for cableapplications By using round 1.6 mm strands with 1-2 kA x strandcapability, itshould be possible to be able to carryvery large DC currents by a reasonably compact cable Unit length for thisstrandislimited by ourbilletsize, of about 40 Kg today, but R&D to go up to 90 Kg iscurrentlyongoing, and a furtherstep to 300 Kg hasbeenalreadyplanned

25. Conclusions.. • Weexpect a bright future for MgB2being a reasonable compromise between pro/cons of LTS and HTS • Having a commercial MRI productnowselling with 18 Km of conductor x system and under operation from as long as 5 yearsflawlessyis a prof that the technologyisconsistent • The relativelylimitedeffortworldwide on MgB2hassomewhatslowed down the conductordevelopment in recenttimes - thatshouldbecomeagainfasterifwemanage to attract more support and understanding of the potential of the material • I amnot a richpersonyet.. but I willdefinitely update you in tenyears