KEK Effort for High Field Magnets Tatsushi NAKAMOTO KEK 1 EuCARD - HE-LHC'10 AccNet mini- workshop on a “High - Energy LHC”, 14 -16 October 2010 Villa Bighi, MALTA
Outline Present R&D Status: < 15 T for HL-LHC • Nb 3 Al Superconductor • 13 T Subscale Magnet • Radiation resistance New Study Towards > 15 T • Stress, Strain Issues Summary 2
Outline Present R&D Status: < 15 T for HL-LHC • Nb 3 Al Superconductor • 13 T Subscale Magnet • Radiation resistance New Study Towards > 15 T • Stress, Strain Issues Summary 3
Motivation to Develop Nb 3 Al Critical current density (Jc) of Nb 3 Sn is higher than Nb 3 Al and advanced magnet technology has been developed by US- LARP…….. Jc vs. B 4000 NbTi(4.2K) 3500 NbTi(1.9K) (NbTa)3Sn(PIT) 3000 Nb3Sn(RRP) Nb3Al(RHQT) 2500 Nb3Al(RHQT) Jc (A/mm2) 2000 1500 1000 500 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 B(T) • Better mechanical performance of Nb 3 Al. • KEK & NIMS has developed RHQ-Nb 3 Al for accelerator HFM application with support by CERN. 4
Nb 3 Al Fabrication Process with RHQ Method: High Jc Mono-filament Nb Jerry-Roll: Nb+Al sheets, Nb or Ta core Nb Multi-filament Ta Precursor (Nb/Al) ~2000 ° C Rapid Heating Quenching (RHQ) (Nb/Al)ss Strand w/o Cu Continuous Electroplating for Ta-matrix Wire Cu stabilization / Area reduction Cabling, Coil Winding 2 nd heating (800 ℃ × 10h) Nb 3 Al A15 strand w/ Cu 5 copper 0.17 mm thick : 50 A/dm 2 , 7 m/h
Cu Stabilized Nb 3 Al Strands with Different Matrix (a) F1 strand (b) K1, K3, K4 strands (c) K2 strand ( all Nb matrix ) ( partial Ta matrix ) ( all Ta matrix ) Ta Nb Nb Ta Nb or Ta Dia. w/ Cu: 1.0 mm Dia. w/o Cu: 0.7-0.73 mm Area Reduction: ~70 % 35 m m Filament Dia.: 4-6 m m * ~2 lots production per Barrier Thickness: year… Twist Pitch: 45 mm 6 * Wire breakings Piece Length: < 1 km (400-ton extruder)
Non-Cu Jc of Nb 3 Al 12T: 1200-1400 A/mm 2 15T: 700-870A/mm 2
Magnetization Curves at 4.2 K Dia 1.0 mm, Cu ratio 1.0, Twist Pitch 45 mm, B ramp 1 T/min, Temp. 4.2 K 400 F1 strand 300 ( all Nb matrix ) K2 strand 200 ( all Ta matrix ) M ( kA/m ) 100 0 -100 -200 K1 strand ( partial Ta matrix ) -300 -400 0.0 0.5 1.0 1.5 2.0 2.5 3.0 B ( T ) 8
Magnetization Curve at 1.9 K 150 K2 strand (all Ta matrix) 100 50 0 M ( kA/m ) -50 0.1 Pure Tantalum -100 0.08 T c ; 4.48 K 4.2 K H c ( T ) -150 0.06 0.04 -200 H c ; 0.01 T (4.2 K) 0.02 0.07 T (1.9 K) -250 0 1.9 K -300 0 1 2 3 4 5 T ( K ) -350 0.0 0.5 1.0 1.5 2.0 2.5 3.0 B ( T ) 9
Demonstration of Cable Fabrication Collaboration with Fermilab • Bonding strength of copper electroplating • Cabling with ceramic insulation >> 28 strands, ~20 m long 13 T Sub-scale magnet Cable test at FRESCA *3 cables available K1 cable: Cu ion-plating (<1 m m) + Cu electroplating (150 m m) 10
Wire Breaking with Ta Matrix Nb 3 Al wires by 400-ton extruder (1-km long wire) since 2004 Nb Matrix # of filaments Ta Matrix • Many wire breakings with Ta matrix. • Breaking initiated at Ta matrix. • Need to reduce breaking rate for long wire production. Nb/Al T >> Quality check, improvement of Ta sheets. a Nb/Al T >> Trials with 7 different Ta ingredients are 11 a underway. T Nb/Al a
Outline Present R&D Status: < 15 T for HL-LHC • Nb 3 Al Superconductor • 13 T Subscale Magnet • Radiation resistance New Study Towards > 15 T • Stress, Strain Issues Summary 12
13 T Sub-scale Nb3Al/Nb3Sn Collaboration with LBNL, Fermilab Hybrid Magnet 22 Different straight length design 20 18 Nb3Al Nb3Sn Current (kA) 16 Operation point 14 of Nb3Sn coil 12 Operation point 10 of Nb3Al coils 8 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 Magnetic field (T) • To demonstrate feasibility of Nb 3 Al cable. • Key design points - The common coil concept, and the shell structure, - Three Nb 3 Al coils & two LBL-Nb 3 Sn coils for Higher Peak Field. 13
Present Status - Coil Fabrication - • 2 practice/dummy coil windings and heat treatment with alumina-ceramic tape completed. • Temperature uniformity in vacuum furnace (800 ° C) verified. • Some vacuum impregnations done, but a leak problem … • The 1st Nb 3 Al coil will be wound in this month. New Development: Thin alumina-ceramic tape (t0.08 mm) Cyanate Ester based resin 14
Development of Cyanate Ester Based Resin Better radiation resistance than Epoxy Resin Collaboration for accelerator HFM application (LHC upgrade): Mitsubishi Gas Chemical: provider of Cyanate Ester resin Univ. of Hyogo: evaluation (bonding & mechanical properties) JAEA: gamma-ray irradiation, evaluation (evolved gas) KEK: coil impregnation, evaluation - 60 Cyanate Ester / 40 Epoxy - low viscosity, low reaction temperature < 150 ° C - pot life: 24hr@ 60 ° C - mechanical strength Not present study. Irradiated at 340K Test at 77K Impregnation trial with dummy coil 15 Fabian and Hooker et. al., presented at “HHH -AMT, Topical Meeting on Insulation and Impregnation Technologies for Magnets”
Neutron Irradiation at Cold Severe radiation in the beam insertion system for the LHC upgrade. Degradation of stabilizers: even below 10 21 n/m 2 (??) - Quench protection is very concerned. Low temperature irradiation facility at KURR (Kyoto Univ. Research Reactor): r0: 0.098 14MeV n on T irrad. from 10 K to 370 K r -irrad : 0.191 Max. fast-neutron flux: 1 x 10 16 n/m²/s (5MW) Cu at 4K (n W m) J. Nucl. Materials, 133&134, p357 (1985) Sample candidates: copper, Nb3Al, (Nb3Sn, HTS), pure aluminum, - Threshold fluence of degradation start - Anneal effect on recovery by warm-up to RT First irradiation test will be carried out in November 2010. Fluence up to 1*10^21/m2. Only 80% recovery by TC to RT. 16
Outline Present R&D Status: < 15 T for HL-LHC • Nb 3 Al Superconductor • 13 T Subscale Magnet • Radiation resistance New Study Towards > 15 T • Stress, Strain Issues Summary 17
Strain Effects on Superconductor Performance of superconductor (A15, HTS) strongly influenced by "Strains". • Measurement with Walter Spring in High Field Magnet. >> Strains applied by fixture. • Residual strains in composite SC due to different thermal contractions. >> D T ~1000 K Could we know the real (3d) strains of SC in composite? 18
Stress/Strain in the SC Coil Stress/Strain issues are unavoidable in HFM for HE-LHC (~20 T). • Coil stress at operation: ~200 MPa at 15T ( > 300 MPa at HE-LHC?) >> Higher local strain at crossover, kink?? • Role of impregnation as reinforcement: w/ or w/o resins Compressive Load How could we have better understanding on local strain behavior in the SC coil? Neutron diffractometer at J-PARC with 10-stack cable sample 19 under various loads would be a nice tooling…
Strain Study at J-PARC Neutron Facility • Currently 120kW >> 1 MW • The “lattice parameter” of Nb 3 Al, Nb 3 Sn, HTS by the neutron diffraction at 4 K to RT, - De / e < 0.005%, penetration depth > 50 mm, - Residual strains of SC wires, - Direct strain measurement under loads, - Strain distribution of stacked cables. • Cryogenic loading frame (4K, 50kN) in JFY2010. • Preliminary test: Clear peaks of Nb 3 Al crystals. Residual strains by different matrixes. • Beam time of 5 days in 2010B approved: >> Nb 3 Al wires (K1-K4, F1), Nb 3 Sn wires (PIT, RRP) from CERN. Cu-(111) Sample Measurement Nb 3 Al Simulation Cu-(200) Cu Simulation Intensity (a.u.) Ta Simulation Cu-(311) Cu-(220) Cu-(222), Ta-(310) Cu-(331), Ta-(400) Ta-(110) Ta-(431, 510) Ta-(211) (310), Ta-(200) Cu-(422), Ta-(420) (622, 630), Ta-(411, 330) Cu-(420) Cu-(440) (420), Ta-(220) Cu-(511, 333) (611, 532) Cu-(400) (521), Ta-(222) Cu-(600, 442) (211) (210) Ta-(321) (321) Ta-(332) (320) (222) Cu-(531) Ta-(422) (421) (400) (520) (200) (332) (610) (440) 20 0.5 1 1.5 2 2.5 3 d (Å)
Strain Study at HFM Lab. at Tohoku Univ. • Collaboration with HFM Lab. at Tohoku Univ. since this year. • SC performance evaluation under various strains. >> Correlation with neutron diffraction measurement at J-PARC. >> Nb 3 Al wires (K1-K4, F1), Nb 3 Sn wires (PIT, RRP) from CERN. 21
Outline Present R&D Status: < 15 T for HL-LHC • Nb 3 Al Superconductor • 13 T Subscale Magnet • Radiation resistance New Study Towards > 15 T • Stress, Strain Issues Summary 22
Summary • Development of Nb3Al superconductor is underway by KEK and NIMS with support of CERN. • Industrialization of Nb3Al must be necessary for practical use. - cost, time, piece length, reduction of breaking, quality control • Magnet technology R&D with Nb 3 Al: - 13 T sub-scale magnet - radiation resistance • For HFM application like HE-LHC, strain study on superconductors (A15, HTS) should be done. Engineering neutron diffractometer would be a nice tooling. 23
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Participants / Collaborators KEK: T. Nakamoto, T. Ogitsu, K. Sasaki, N. Kimura, S. Kin, A. Terashima, K. Tsuchiya, Q. Xu, A. Yamamoto, NIMS: A. Kikuchi, T. Takeuchi, N. Banno In cooperation with: CERN: L. Rossi, G. de Rijk, L. Bottura LBNL: G. Sabbi, S. Caspi et al. Fermilab: A. Zlobin, E. Barzi, R. Yamada CEA/Saclay: B. Bourdy et al. 26
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