1. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Challenges to design (construct) and test fast ramped superconducting dipole magnets P.Fabbricatore INFN-Genova, Italy In the years 2007-2012 INFN developed and tested a prototype of a superconducting fast cycled dipole magnet for FAIR SIS300 synchrotron. Ac losses and field quality were relevant (fundamental) parameters for the design. In this talk I will briefly summarize the experience on these aspects. We will see that high ac losses are partly due to mechanisms intrinsic to superconducting cable and partly to eddy currents in mechanical structures. Dynamic multipoles are mainly due to to sc cable. Some considerations for SC magnets in hadrontheraphy done at the end. This presentation is based on the work of many colleagues of INFN and GSI working in the frameworks of DISCO_RAP (INFN project) and CRISP WP5 (EU-FP7)

2. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach SIS300 dipoles: fast cycled and curved magnet 100 Tm (1.5 T) 300 Tm (4.5 T) 1 T/s

3. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Ramp 1T/s  ac losses  Premature Quench  Costs of Cryogenics  Dynamic multipoles Hence: Development of a low loss conductor Design with loss minimization (taking care of eddy currents in structures) 10 7 cycles  Fatigue  Mechanical design and materials optimization Aperture (mm) B (T)dB/dt (T/s)  (T 2 /s) Q (W/m) LHC538.340.0080.0670.18 RHIC803.50.060.210.35 SIS3001004.51 <10 Criticities of SIS300 dipoles in respect of the fast ramp Consideration: If you are fact cycling a magnet, you probably want the the magnet performing many cycles. This is indeed tha case of SIS300:

4. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Basic Mechanisms in the superconducting cable 1-Persistent currents in superconducting filaments This contribution is important both for ac losses and multipoles (b3, b5) but...while for ac losses the fast ramp can cause large power loss (in W), from field quality point of view nothing change wrt static case. THE PERMANENT CURRENT IS NOT REALLY A DYNAMIC EFFECT! Strand diameter (mm)0.826Number of strands36 Filament diameter (µm) Number 2.5 ~40000 Core Cable dimensions (mm) 1.362/1.598 x 15 Interfilament matrix Cu-Mn Ic@5T, 4.2K (kA)>18

5. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Effect of persistent currents on DISCO_RAP dipole Field quality is depressed at low field. This effect is independent on ramp rate Ac losses at 1T/s of the magnet are as high as 3W/ at low field and 1.8 W at maximum field Ref. M. Sorbi, F. Alessandria, G. Bellomo, P. Fabbricatore, S. Farinon, U. Gambardella and G. Volpini. Field Quality and Losses for the 4.5 T Superconducting Pulsed Dipole of SIS300 - IEEE Trans.Appl.Supercond.,18,138

6. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach 2- Inter-filaments coupling currents This a completely dynamic effect contributing to both ac losses and perturbation of the field quality. It can be kept as low as possible by reducing the twist pitch (p) or increasing the transverse resistivity

7. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Effect of IF coupling currents on DISCORAP dipole In terms of field quality at 1T/s the coupling currents contribute for maximum 0.6 unit (about 17% with respect persistent currents). In terms of ac losses for 1 W/m (about 1/3 of the persistent current).

8. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach R&D on conductors for limiting the IF coupling currents: try to reduce twist pitch and transverse resistivity Ic degradation due to twist pitch for 0.825 mm wire For the transverse resistivity, from measurements we got ρ t = 0.3 nΩ m at 0 T. This value is somewhat lower than the value predicted by the computations, 0.46 nΩ m. We suspect that the high filament distortion, may have broken the Cu-Mn sheath surrounding the filaments, putting the Nb-Ti in direct contact with the bulk Cu matrix, and thus lowering the transverse resistivity Low Loss Nb-Ti Superconducting Rutherford Cable Manufacture for the SIS300 INFN Model Dipole By: Volpini, G.; Alessandria, F.; Bellomo, G.; et al. IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY Volume: 21 Issue: 3 Pages: 3334-3337 Part: 3 Published: JUN 2011

9. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach An intensive R&D activities for developing fine filaments immersed in a Cu-Mn matrix Investmement of the order of 700 k€. Only six lengths (350 m each) produced Two firms involved in strand production. Only one was able to produce significant lengths (the second one has just produced long strand lengths last month) Many breakages during wire production A low loss wire will be one of the main issues for future developments

10. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach 3- Inter-strand coupling currents Two kinds of coupling: a) opposite strands; b) adjacent strands 2c 2b A ss core cuts down this term

11. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach B 0 (T) 0.5 db 3 / db 5 1.5 db 3 / db 5 3.0 db 3 / db 5 4.5 db 3 / db 5 Excel code0.03 / -0.080.01 / -0.030.00 / -0.01 Roxie0.04 / -0.150.01 / -0.040.00 / -0.020.00 / -0.01 Sextupole and decapole field harmonics (units) due to inter-strands coupling currents at r=35 mm In terms of field quality at 1T/s the inter-strand coupling currents contribute for maximum 0.15 unit (completely negligible with respect persistent currents). In terms of ac losses for 0.45 W/m (about 20% of the persistent current). Once again the dynamic effects reflect in large ac losses rather than in significant perturbation of the field quality!

12. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Ac losses in the magnet body (no end coils contribution) SIS300 4.5T 100mm boreA (future) LHC injector @ 4T Total loss when ramping from 1.5T to 4.5T at 1 T/s: 7.7 [W/m] Total loss when ramping from 0.4 T to 4.0T at 1.5 T/s: 15.5 [W/m] Hysteresis30 % D fil effect =3.5  m (2.5  m geom. 3  m eff.) 30% Coupling Strand9 % CuMn ρ t = 0.43 nΩ·m (0.3 nΩ·m ) lp 5 mm (7 mm ) 11% Interstrand Ra+Rc6 % Cored cable 7% Total conductor(45 %)(48%) Collars + Yoke eddy + Prot. sheets 6 % Collar 3 mm tick Iron 1 mm tick 7% Yoke magn24%H c (A/m)=3517% Beam pipe14 % Collar-Keys-Pins8 %10% Yoke-Keys-Pins3 %4%

13. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach At 1 T/s the effects on field quality due to eddy currents in metallic structures are negligible (if yoke and collars are laminated), but at coil ends (B field normal to lamination) Laminated (1 mm) yoke Laminated (3 mm) ss collar The eddy currents in beam tube just affect only dipole field

14. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach AC losses measurement done during the magnet test at INFN-LASA AC Losses Measurement of the DISCORAP Model Dipole Magnet for the SIS300 Synchrotron at FAIR By: Volpini, G.; Alessandria, F.; Bellomo, G.; et al. IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY Volume: 24 Issue: 3 JUN 2014 Field ramp rate [T/s ] Reduced power loss [J/T]

15. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach … and what about field quality during ramp? Not yet a result for this magnet (to be tested at GSI). We can look at the experience with GSI001 (GSI BNL collaboration). A RICH type short dipole with not optimized strands (but a cored cable) b3 b5 Presented by G.Moritz at ECOMAG-05 Frascati

16. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach Central field (T)2.03 Curvature radius (m)3.31 Over all current density (A/mm 2 ) 52 Current (A)1000 Turns189 Inductance (H)1.8 Stored Energy (MJ)0.9 Weigh (t)41 GFR (mm × mm)(200 × 200) Field uniformity in the GFR < 5 10 -4 Iron yokeLaminated (1mm) warm CoolingIndirect (cryo-cooler) Coil supporting structureAl alloy Extrapolating: some considerations regarding ac losses in sc dipoles for gantries in hadrontheraphy Cross section of an iron dominated 90 degree magnet. dB/dt (T/s)P hysteretic P is P Ra P eddy P structure P total 0.11.50.21.110.44.2 0.23.00.64.53.81.513.4 0.34.51.310.18.53.427.8 0.46.02.318.015.26.047.5 For a treatment we calculated in total a loss of 487 J in 30 s giving 15.83 W of average power. This value is too high for being removed in steady state condition by cryo-coolers

17. Challenges to design and test fast ramped superconducting dipole magnet P.Fabbricatore INFN-Genova Beam Dynamics meets Magnets-II 1-4 December 2014 Bad Zurzach CONCLUSIONS When involving superconducting magnets the field rate limitations are mainly determined by ac losses. The corresponding practical field rates (few T/s) should not be an issue for the field quality if looking at the eddy currents in metallic structures and yokes Excluding the permanent currents, affecting field quality also in dc conditions, the intrastrand coupling currents are the major (but not dramatic) source of field quality perturbation.