Prospects of MgB 2 Superconductor in Energy and Magnet Applications

Transcription

1 Prospects of MgB 2 Superconductor in Energy and Magnet Applications S. Berta, S. Brisigotti, V. Cubeda, M. Palombo, D. Pietranera, L. Rostila, A. Tumino, and G. Grasso November 4 th, 2010

2 Outline Considerations on MgB 2 The ex-situ manufacturing process Main properties Industrial production Applications Conclusions

3 Considerations There is a significantly growing interest towards LHe-free applications of superconductivity Superconducting windings operated above 10 K will profit from a higher stability and reluctance to quench Easier installation and operation in a non-ideal environment are in favor of a cryogenic-free system Operation at higher temperatures helps making superconducting devices, particularly AC, more efficient and competitive Superconducting devices become more competitive on large scale devices, therefore R&D and prototyping are high risk activities

4 Considerations Adequate conductor protection in case of a magnet quench, particularly in large stored-energy windings, obliges one to add significant quantities of stabilizing material, that reduce the engineering critical current to a level that might be well below the superconductor current density Most of these large devices (motors, heaters, MRI, etc.) do not frequently need the production of a magnetic field higher than 2-5 Tesla Very long lengths exceeding several Km are required to reduce the number of joints and make the magnet manufacturing cheaper and faster Round/rectangular wires with low aspect ratio (1:2, 2:3) are highly desirable for simpler solenoid winding React & Wind conductors make series production of windings much more attractive

5 Is MgB 2 representing a possible solution? It currently represents a reasonable compromise between the present status of LTS and HTS materials Composition MgB 2 High enough for 20K operation Critical temperature 39 K High enough to reduce weak links Coherence length 5 nm Nanoparticles are propedeutic for high j c (B) Penetration depth 120 nm High enough to produce useful fields Upper critical field T MgB 2 development makes sense only if it has very attractive /kam!

6 I c /I c (Zero External Strain) T Upper critical field H c2 [T] Very simple crystal structure MgB 2 Polycristalline materials carry large currents Very high current densities observed in films Moderately high T c Sample No. 1 Sample No. 2 2 T c of 39K Good mechanical properties K(Liq. He) 4T Tape Surface 4 Soldered to SUS304 Rig External Strain (%) MgB 2 presents very promising features Low cost low weight MgB 2 precursors: 250 /Kg today MgB 2 mass density: 2.5 kg/dm 3 Factor of 10 larger than in bulks; room for large improvement in wires still available from R&D Potentially high critical field bulk dirty limit thin film dirty limit wire SiC doped clean limit Temperature [K] Larger than 60 Tesla at low T

7 Enhancements in the P.I.T. ex-situ method Possible routes: + B Mg MgB 2 Commercial precursors B Mg MgB 2 + MgB 2 (doped) Doped boron B(doped) Mg + B + dopant Commercial MgB 2 Home made boron MgB 2 B + Mg B 2 O 3 High energy ball milling tube filling wire drawing to 2 mm cold rolling reaction at

8 MgB 2 -> Boron Control of powder production process is crucial to achieve optimal particle size -> j c (B) Commercial MgB 2 30 μm MgB 2 from commercial Boron 1000 nm 450 nm MgB 2 from special Boron

9 Requirements for applications High field performance demonstrated in R&D wires by many groups

10 MgB 2 wire development Ex-situ PIT process Columbus plant in Genoa Chemical phase Metallurgical phase Has its own production facilities in Genoa with leading capability to produce and supply MgB 2 wires on a commercial basis since three years most used for MRI so far Manufacturing of MgB 2 wires by simple exsitu Powder-In- Tube method The new plant is operational for a wire production readily scalable up to Km/year if requested by the market in 3-6 months time Wire unit length today up to 4 Km in a single piece Total plant area m 2 60% of it in use today Production for MRI so far exceeded 500 Km of fully tested wires MgB 2 compound production now also fully implemented Increased interest from developing power applications B + reaction at 900 C in Ar MgB 2 Mg + Great flexibility on wire design compared to HTS

11 MgB 2 development Our MgB 2 production process (ex-situ) is unique as it allows to: Manufacture flexible wires (Ɛ cr 0.5-1%) Use low cost precursor materials Production process similar to LTS Reach considerable performance at moderate fields ( up to 5 Tesla so far) Manufacture very long lengths with a scalable process (up to 4 Km already today) Manufacture conductors of virtually any shape/size/matrix materials with comparable performance What we produce and supply today totally fits with our low-cost, easy scalability strategy Production of MgB 2 wires in our Company is expected to grow twice each year for the next three years Because of the higher volumes and optimized manufacturing methodologies, from it is expected that the conductor price would have reached its final target value within 20 40%

12 Monolithic design Two basic monolithic wire designs for magnet application are currently under production Currently produced in three sizes (w x t): 2.5 x 1.5, 2 x 1, 1.5 x 0.7 mm A) Nickel 201 Iron 99.5% Copper OFHC C10200 MgB 2 Monel 400 B) Nickel 201 Copper OFHC C10200 MgB 2 Monel 400 Type A): Standard Columbus MgB 2 wire with one ring of superconducting filaments Iron barrier between the filaments and the Copper core Type B): Newer MgB 2 wire with no Iron barrier between the filaments and the Copper core higher engineering critical current and no Iron content in the conductor, MgB 2 filaments more near to the neutral plane to enhance resistance to bending long lengths under development Drawback of the monolithic wire design: Copper fraction hard to be varied significantly

13 Expected wire performance evolution with respect to time Type A) wire Time Process J e (A/mm 2 ) at 10K, 2 T J e (A/mm 2 ) at 10K, 4 T Now Carbon doping Early 2011 Ball milling End 2012 Improved Boron High pressure process For type B) wire we do expect 10% higher J e J e calculated overall (entire wire cross section) J e at first approx is independent from the overall wire cross section S, i.e. I c can be calculated by I c =J e x S For approximate numbers at 20K, just divide magnetic field by a factor of two ( i.e. J e at 20K, 2 T ~ J e at 12K, 4 T)

14 Other wire configurations These conductors are conceived for conventional magnet application Different wire designs can be produced according to customers request (low AC-losses, high filaments count, wire-in-channel, etc.) Sandwich conductor is becoming our best proposal for a magnet wire f.f. of 30%, adjustable Copper fraction, lower cost, higher overall j e, easier than WIC for MgB 2

15 Jc [ A/cm2] Titanium sheath Titanium as been used as matrix material instead of Nickel, because of its higher resistivity and amagnetism Preferable solution for AC applications Ni Nickel alloy Titanium alloy Ti MgB Undoped MgB Ni MgB 2 Ni 2.5 T = 5 K ,5 1 1,5 2 2,5 3 3,5 4 4,5 5 applied field [ T ] MgB 2

16 MgB 2 device development Texas Center for Superconductivity 1 Tesla cryogenic-free solenoid magnet ASG Superconductors Open-Sky MRI Brookhaven National Laboratory Cryogenic-free pancake magnet INFN-Genova 2.35 Tesla dipole magnet for particle physics Ansaldo Breda CRIS 1 Tesla cryogenic-free solenoid magnet Some of the devices recently realized employing W&R Columbus MgB 2 wires CERN MgB 2 cable with Ic>17 ka, 6 mm in diameter Scaled up to 125 ka on a 62 mm cable SINTEF Norway Induction heater Cesi Ricerca LNe Fault current limiter Chinese Academy of Science 1.5 Tesla cryogenicfree solenoid magnet

17 The Magnet MR Open Magnet assembly The magnet consists of a U-shape ferromagnetic yoke and two MgB 2 coils (one for each pole, 12 DP total) Main Magnet Parameters Nominal Field Peak Field on the Conductor Nominal Current Conductor critical current 0.5 T 1.3 T 90 A 400 A Conductor price ( /kam) at 20 K, 1 T < 7 Number of Pancakes 12 Conductor Length (total) Inductance Overall Dimensions Patient Available Gap Weight 18 Km 60 H 2x2x2.4 m 0.6 m Kg A number of full magnets already produced new generation currently under development

18 To be soon constructed in Russia within a partnership with Italy This Tokamak is very compact ( about 6 m diameter), and basically consists of Copper coils cooled to cryogenic temperatures, due to the extremely high magnetic field ( >> 20 Tesla ) Cooling technology compatible with the use of MgB 2 The outer poloidal field coils experience a field which is compatible with today s MgB 2

19 Ignitor italian fusion project Parameters Symbol Value Unit Major Radius R m 0.47, Minor radius a,b m 30K He gas cooled 0.86 copper conductors are Aspect ratio A 2.8 currently expected to Elongation k 1.83 be used in this Triangularity d 0.4 machine Toroidal magnetic field B T 13 T Toroidal current I p 11 MA Maximum poloidal field B p,max 6.5 T Mean poloidal field 3.44 T Poloidal current I q 9 MA Edge safety factor (@11MA) q y 3.6 Confinement strenght 38 MA T Plasma Surface S 0 34 m 2 Plasma Volume V 0 10 m 3 ICRF heating (140 MHZ) P RF 6 (*) MW

20 MgB 2 cable conductor for Ignitor

21 Construction of a DC induction heater 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 Cryogenic system has been recently tested One of the two superconducting coils has been tested successfully

22 Design of an MgB 2 feeder system to connect groups of superconducting magnets to remote power converters 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

23 20kV distribution system DC resistive FCL design based on MgB 2 Nominal Rate Nominal Voltage Quenching current Inductance Quenched resistance 25 MVA 20 kv 1225 A 5 mh 5 Cross section mm 2 Number of MgB 2 filaments 8 Superconducting section 19.1 mm 2 Stabilization material Cu Sheath material Steel Quenched resistance per unit length 0.1 /m

24 Racetrack magnet for particle accelerators MARIMBO project The magnet reached about 2.5 Tesla in cryogenic-free conditions Magnet was R&W with a layer by layer structure

25 Conclusions Our MgB 2 wire production is steadily improving and showing satisfying reproducibility and reliability Low cost raw materials and techniques have to be used in order to bring MgB2 to the 1 /kam price vs performance target within the next 3-5 years Due to the incompatibility of MgB 2 with Copper, the sandwich conductor will be one of our low-cost solution for magnet applications in the upcoming future The market conditions and R&D opportunities we are experiencing are making us confident that the growth rate of MgB 2 production and use will meet our targets