F. Kircher (CEA Saclay/DSM/Irfu/SACM) December 15, 2008

F. Kircher(CEA Saclay/DSM/Irfu/SACM) December 15, 2008 Some points about the superconducting magnet for a CLIC detector

Summary • Introduction • Geometrical, electrical, magnetic and mechanical parameters • Limits • Conductor possible improvements • ILD detector magnet • Conclusions

Introduction • CMS magnet tests were very successful • For the next colliders (ILC, CLIC), most of the detector magnets are CMS-like • Nevertheless, some questions may be asked, such as: • . what are the relevant parameters? • . what is the ultimate limit for such magnets? • . which improvements can be done on CMS elements? • We will give some directions in this presentation (technical aspect, not cost)

Magnet parameters • Three basic parameters for the design: • B0: central field • Ri: coil inner radius (typically: Ri = Rbore + 250 mm) • L: coil length • Other relevant parameters: • Field homogeneity • Fringing field • Coil thickness (in term of radiation length)

CMS Detector (Compact Muon Solenoid) . Superconducting solenoid: 6 m bore diameter 13 m length 4T central field + iron yoke . No special request on field homogeneity . Cold mass thickness: 3.9 X0

From design to realization : 1998-2006 Central field : 4 T Nominal current : 20 kA Stored energy : 2.6 GJ Cold mass Length : 12.5 m Internal diameter : 6.4 m Weight : 220 t

Stored energy of SC magnets An important parameter for magnet safety Among detector magnets, , CMS has both : • the largest stored energy (2.6 GJ) • the largest density of stored energy (11.6 kJ/kg) A value around 12 kJ/kg is now considered as a safe standard for CMS-like magnets

Stored energy/per unit of cold mass E/M (from A. Hervé)

CMS parameters and what can be varied (from A. H.)?

Fringing field • Important parameter: . for the workers around (or in) the magnet . for some hardware (relays, pumps…) . for the other detector in push-pull operation • Unfortunately, in these huge yoke structures, gaps are needed, both for cable passages and for assembly reasons • CMS has an in equivalent iron thickness of about 1.5 m, and is rather field-leaking (typically 500 G near the outside part of the barrel yoke) • For ILD, the foreseen iron thickness is more around 3 m. Nevertheless, because of the gaps, the fringing field is still around 200 G at 2 m outside the yoke • As the mass of iron is huge, both specifications and gaps must be as reasonable as possible • Note also that the metallic structure of the buildings affects the calculations

Actual limitations • My personnal criteria (from experience) B02 * Rc ≤ 60 T2 * m (complementary to the other criteria, where neither B0 nor Ri appear) . CMS: 42*3.2 = 51 T2*m . LDC: 42*3.6 = 58 T2*m . SiD: 52*2.6 = 65 T2*m • Theseare physical, and cost, and not so much technical limitations • The length L is important in the aspect ratio L/Rc for field homogeneity and efficiency of A*t

Summary • Introduction • Geometrical, electrical, magnetic and mechanical parameters • Limits • Conductor possible improvements • 5 ILD detector magnet • Conclusions

CMS conductor Electron beam welding Thermal stabilizer: very high purity aluminium: 99.998% Superconducting cable (32 strands) Mechanical reinforcement: Aluminium alloy 6082 T5

Improved CMS conductor (1) • Replace pure aluminum stabilizer by: • cold drawn Al-0.1wt%Ni alloy • developed for the ATLAS thin solenoid superconductor(A. Yamamoto et al.)

Improved CMS conductor (2) • This proposal was done by several labs involved in the CMS magnet few years ago • Unfortunately, up to now, no funding could be found • Nevertheless, this development is important to be done for future projects: • . the electrical stability will not be affected (RRR* of 500 for CMS overall conductor, starting from a RRR of 3 000 for very pure Al) • * RRR = resistivity at 300 K / resistivity at 10 K • . the mechanical stability will be improved (about 100% of structural material in the conductor, vs about 60% for CMS).

Changing the mechanical stabilizer welding • This is an other way • The EBW (electron beam welding) method used for CMS is costly (about 40 % of the total cost of the conductor) and tricky • Other ways were foreseen during the CMS conductor R&D phase, but not too much time was available for the necessary developments: • . soft soldering • . friction • . laser beam • As some of these methods have been progressing in the last 10 years, it is worthy to do at least some research and reflexion

Cable in conduit conductor? Developed for fusion magnets, with very high fields (10 -12 T range), and high losses Drawbacks: . low current density . short unit length . expensive Not suitedfor medium-range field , DC magnets , as are detector magnets

Version ILD-V2 Saclay Parameters used for ILD-V2 detector magnet: . B0 = 4 T nominal, 3.5 T operation . Rint coil = 3 590 mm . Rext coil = 3 940 mm . L coil = 3 672 * 2 mm Stray field (@ 3.5 T): . Bext ≤ 200 G @ z=10 m from I.P. . Bext ≤ 50 G @ at 15 m in the radial direction Homogeneous field in the TPC volume: z max l (R) = ∫ (Br (R) / Bz (R) dz ≤ 10 mm 0 within the TPC volume: z max = 2.25 m, R max = 1.8 m

Version ILD-V2 Saclay: field homogeneity The field homogeneity is ajusted with: • a FSP (Field Shaping Plate) inside the endcap yoke • and correction currents in some places of the coil (3 inner layers of the two modules at extremities).

ILD-V2: main outputs Electrical parameters (4 T) Inom (kA) 15.9 Eng. J (A/mm2) 9.6 (for Inom) Icor (kA) 18.1 (3 layers * 2 modules) Stored energy (GJ) 2.0 Ws density (kJ/kg)12.2 Integral homogeneity in TPC volume (mm) ≤ 9 Yoke dimensions Rout barel yoke (mm) 7 110 Zout endcap yoke (mm) 7 190

ILD-V2 SACLAY configuration @ 4 Tesla Iron : up to R=7.110m (2.76m thick), up to Z=+/-7.190m (3.27m thick) + 100 mm FSP (Field Shaping Plate) Coil : 4 layers ,7.35 m length subdivided in 5 parts ILD-V2 Br/Bz(z=0 to 2.25 m) for r=0 to 1.8m Bz(r=0) (Br/Bz) vs r (z=0 to 2.25 m) 600 Gauss B(z) (8m<r<9.5m)

Conclusions • CMS detector magnet was a huge step from detector magnets of the LEP generation (Aleph, Delphi) • Because of physical and economical reasons, a similar step is not realistic for the after-LHC detector magnets • Nevertheless, the CMS, and also the ATLAS, experience must be used for the design and realization of the future magnets • Some basic parameters, limitations and directions for R&D concerning the conductor have been mentionned in this presentation. As an application, the work going on for an ILC detector magnet has been briefly presented

F. Kircher (CEA Saclay/DSM/Irfu/SACM) December 15, 2008