Shielding Magnetic Fields Of Several Tesla: The FCC SuShi Project
Shielding magnetic fields of several Tesla: the FCC SuShi project http://cern.ch/sushi-septum-project Kristóf Brunner, Dániel Barna Wigner Research Centre for Physics, Budapest, Hungary Miro Atanasov, Alejandro Sanz-Ull CERN K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 1
The Future Circular Collider Baseline: 50 50 TeV proton-proton collider 100 km ring Using existing CERN infrastructure as injector Targeted problem: extraction of the 50 TeV beam towards the beam dump K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 2
Extraction scheme Beam is dumped when: Something misbehaves At the end of the cycle K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 3
Doing it at the LHC: the Lambertson septa B 1.2 T Coils Iron yoke Mu-metal layer on vacuum chamber Circulating & extracted beams S. Bidon, et al: Steel septum magnets for the LHC beam injection and extraction, Proc EPAC 2002 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 4
Doing it at the LHC: the Lambertson septa B 1.2 T Coils Iron yoke Mu-metal layer on vacuum chamber Circulating & extracted beams Using μr 1 to „suck out” the field lines from the circulating beam Can't go above 1.5 T due to saturation of iron S. Bidon, et al: Steel septum magnets for the LHC beam injection and extraction, Proc EPAC 2002 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 5
FCC parameters for extraction At top energy (most difficult): Septum integrated field Available space for septum 190 Tm 120 m } Need 2 T field (to accomodate gate valves, pumps, etc) (Space would be even more tight in the „high-energy LHC” - LHC tunnel with FCC technology) B 2 T (target: 3 Tesla) – Not easy with normal-conducting devices – need superconductors? Must follow the ring energy to be ready for beam-abort at any time (quasi-DC mode) Field homogeneity: 1% Leakage field at circulating beam: 10-4 relative K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 6
Doing it at the FCC: the SuShi idea If cooled down in 0 field, a superconductor can shield the outside field Persistent currents Homogeneous high field 5-7 cm Concept is similar to eddy current septum, but can work in DC mode, (because the eddy currents are persistent) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 7
Doing it at the FCC: the SuShi idea If cooled down in 0 field, a superconductor can shield the outside field Persistent currents Homogeneous high field 5-7 cm Concept is similar to eddy current septum, but can work in DC mode, (because the eddy currents are persistent) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Using μr 1 material to expel the field lines Stray fields workshop, 2017, slide: 8
Pros & cons Pros Shielding currents arranged by nature (high precision zero field) Continuous 2D current distribution (unlike a winded magnet) perfect shielding Bulk shield, better mechanical, and thermal stability Cons Superconductor in high rad zone (quench) Hysteretic behavior, always have to start from virgin state To erase ‘memory’ of shield, temperature has to be increased Highest possible current density(critical state model) thinnest shield K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 9
Combining μr 1 and μr 1 The „magnetic cloak” μr 2 2 2 2 R R 2 1 2 1 R R R1 Ferromagnet absorbs the induction lines expelled by the superconductor Seems a natural choice, since it does not distort the external field R2 μr 0 Does not work for FCC with realistic geometrical parameters: field in ferromagnet would be too high: 13-18 T K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 10
Homogeneity at various field strengths Flat wall homogeneity despite significantly different penetration depths At injection pos. winding neg. winding 0.5 T At top energy 3T K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 12
CERN Bubble chambers In the '70ies: superconducting tube to shield high magnetic field To introduce low-momentum particles into the high field of the bubble chamber Different materials, and techniques could bring the shielded field strength from 2 T up to 5.9 T Superconductor tube M.Firth, et.al.: Performance of the superconducting field shielding tube for the CERN 2m hydrogen bubble chamber M.Firth, L.Krempasky, F.Schmeissner: Preliminary work on field-free particle beam paths from hollow superconducting shielding tubes – Proc. 3 rd. Int. Conf. Magn. Tech. (1970) 1178 tore/ Public/46/027/46027030.pdf K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 13
SLAC B F.Martin, S.J.St.Lorant, W.T.Toner: A four-meter long superconducting magnetic flux exclusion tube for particle physics experiments – NIM 103 (1972) 50 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 14
MgB2 450 mm Produced by the Reactive Liquid Magnesium Infiltration (RLI) process (G. Giunchi, Int.J.Mod.Phys.B17,453) Extra large boron grainsize (160 μm) to be stable against flux jumps (G.Giunchi et al, IEEE Trans. Appl. Supercond. 26, 8801005 ) 8. 5 m m 50 mm K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 15
Testing of prototypes at SM18 LHC corrector magnet MCBY Shield Long aluminium support tube Hall sensors Transverse alignments K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 16
MgB2 magnetization cycle Field outside the shield Field inside the shield K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 17
MgB2 magnetization cycle 2 minute plateaus for relaxation measurement Ramp rate: 0.1 A/s 5 mT/s on external sensors (realistic for FCC: 3 T/10 minute) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 18
MgB2 magnetization cycle Smooth penetration at 2.6 T Complete shieldig below 2.6 T K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 19
MgB2 magnetization cycle No flux jump on the virgin curve up to the highest field Flux jumps at low fields, after the shield has been exposed to high fields Smooth penetration at 2.6 T K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 20
MgB2 magnetization cycle K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 21
MgB2: field penetration 2.6 T plateau (full shielding) OUTSIDE Significant creep on the plateaus (smooth, not an avalanche-like jump!) INSIDE 64 A magnet current K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 22
MgB2: field penetration 2.6 T plateau (full shielding) OUTSIDE Significant creep on the plateaus (smooth, not an avalanche-like jump!) Full shielding ( 0.1 mT) deeper inside Field penetration at open end of the tube INSIDE INSIDE K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, 88 mm from shield's end Stray fields workshop, 2017, slide: 23
MgB2: linearity Measured external magnetic field is non-linear as a function of magnet current! K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 24
MgB2: linearity realistic MgB2 Jc(B) J0 exp( – γ B) Increasing field more penetration Effective shielding surface drifts away from Hall sensor Less field concentration at sensor COMSOL simulation in precise model of MCBY magnet Hall sensor K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 25
MgB2: linearity realistic MgB2 Jc(B) J0 exp( – γ B) COMSOL simulation in precise model of MCBY magnet Hall sensor J0 and γ are strongly correlated K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 26
MgB2: linearity realistic MgB2 Jc(B) J0 exp( – γ B) COMSOL simulation in precise model of MCBY magnet Hall sensor J0 and γ are strongly correlated K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 27
MgB2: linearity realistic MgB2 Jc(B) J0 exp( – γ B) COMSOL simulation in precise model of MCBY magnet Hall sensor J0 and γ are strongly correlated K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 28
MgB2: linearity shield inner surface From observed nonlinearity one can get some info on Jc(B) At 64 A different parameters give B penetration profiles with same, almost full depth B profiles 1.5 mm shield outer surface 64A 60A 40A 50A 30A 20A 10A Shielding current profiles K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 29
HTS tape covered tube m 450 m Ø46.5 mm Layers overlapping Copper support 25 layers of helically wrapped tube SuperOx 2G HTS tape, softsoldered Little current loops K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Superposition Stray fields workshop, 2017, slide: 30
HTS: Shielding performance No flux jumps! Smooth, full penetration above 0.25 T Due to limited Jc? Shielding up to 0.25 T (not perfect, as we will see!) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 31
HTS: penetration at low field! Continuous penetration from zero field! Attenuation is about 10-3 here Due to geometry? (non-continuous geometry, small gaps between tape layers, small current loops) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 32
NbTi/Nb/Cu multilayer shield Consists of multilayer sheets of 0.8mm, containing 30 layers of 9 µm NbTi From previous tests it seems possible to shield 2.5T field with 3 sheets ( 2.4mm) A 4-sheet shield will be tested in the beginning of next year I.Itoh, K.Fujisawa, H.Otsuka: NbTi/Nb/Cu Multilayer Composite Materials for Superconducting Magnetic Shielding, Nippon Steel Technical Report No. 85, January 2002 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 33
Shielding performance NbTi/Nb/Cu multilayer sheet (various conditions) [1] Exponential Jc(B) J0·exp(-γB) leads to exponential increase of required thickness: d d0·exp(γB) with d0 1/γμ0J0 Large-grain MgB2 (estimates from our tests, using simulation) For MgB2: roughly x3 increase for 1 T [1] I.Itoh, T.Sasaki, Cryogenics 35 (1995) 403 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 34
Shielding performance MgB2 cheaper NbTi/Nb/Cu multilayer sheet (various conditions) [1] Exponential Jc(B) J0·exp(-γB) leads to exponential increase of required thickness: NbTi perfo more rman t Large-grain MgB2 (estimates from our tests, using simulation) d d0·exp(γB) with d0 1/γμ0J0 For MgB2: roughly x3 increase for 1 T [1] I.Itoh, T.Sasaki, Cryogenics 35 (1995) 403 K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 35
Outlook Passive superconductors: – Perfect shielding if thickness is sufficient – Up to very high fields – DC and AC mode – Very attractive if space is tight – Very versatile: MgB2: large bulk, complex shapes, EDM machining, cheap NbTi multilayer: ductile, robust, formable Future plans: – Measurement of third prototype – Construct a full demonstrator K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 36
Thank you for your attention! Acknowledgements FCC Study group CERN SM18 (M. Bajko, H. Bajas, M. Strychalski) CERN TE-MSC-MM (C. Petrone, M. Buzio) CERN TE-ABT (B. Goddard, J. Borburgh, M. Atanasov, A. SanzUll) G. Giunchi (MgB2) A. Molodyk (SuperOx) European Commission (FP7/EUCARD-2, grant agreement no. 312453) Hungarian Academy of Sciences Wigner Research Centre for Physics, Budapest K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 37
Additional slides K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 38
Measurement possibilities Rotating coil to measure field quality (during tests only) Shield thick enough to ensure perfect shielding safely. Most important: detect flux-jumps (very quickly and reliably) beam abort Hall sensors close to the shield (off the mid-plane) (tests & real app. ?) Hall sensor to measure the „zero field” (during tests only) Do not need to be high precision Pick-up coil to detect fluxjump (tests & real app.) K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 39
MgB2: long-term relaxation If external field at a safe level below full penetration. .relaxation is small, can be compensated by the excitation current K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, 0.25% Stray fields workshop, 2017, slide: 40
K. Brunner, D. Barna: Shielding magnetic fields of several Tesla: the FCC SuShi project, Stray fields workshop, 2017, slide: 10 Combining μ r 1 and μ r 1 The „magnetic cloak" R 1 R 2 μ r 0 μr R2 2 R 1 2 R2 2 R 1 2 Ferromagnet absorbs the induction lines expelled by the superconductor Seems a natural choice, since it does not .
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