CERN, Geneva (European laboratory for Particle Physics)

2 L. Dassa What is CERN ? CERN is the European Organization for Nuclear Research, the world's largest particle physics centre. Here physicists come to explore what matter is made of and what forces hold it together. Founded in 1954, the laboratory was one of Europe's first joint ventures and includes now 21 Member States. 2014: 21 Member States: A, B, BU, CH, CK, D, DK, E, F, GB, GR, H, I, N, NL, PL, P, S, SF, SK, IL Size: 490ha F, 112ha CH Budget : 1280 MCHF (~825MEuros)

3 L. Dassa Who works at CERN ? CERN employs representatives of a wide range of skills - physicists, engineers, technicians, craftsmen, administrators, secretaries, workmen,… Staff members: ~2550 ~81 physicists in research ~977 engineers ~862 technician ~427 clerks and administrative ~203 hand workers Fellows: 215 Scientific associates : 293 Users: ~ 6200 coming from 483 institutes and universities with 80 nationalities And about 2000 peoples from external enterprises

4 L. Dassa The Large Hadron Collider (LHC) Some numbers: ~ 5,000 LHC superconducting magnets ~ LHC cryogenics need 40,000 leak-tight pipe junctions ~ 12 million liters of liquid nitrogen are vaporized during the cool down of 31,000 tons of material and the total inventory of liquid helium is 700,000 liters. The LHC, the world’s largest and most powerful particle accelerator, is the latest addition to CERN’s accelerator complex. It mainly consists of a 27 km ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.

5 L. Dassa ATLAS: A generic LHC experiment / CMS: Compact Muon Solenoid

6 L. Dassa EN/MME GROUP 1 INTERNAL CONTRAT (30 P.) & 2 EXTERNAL CONTRATS

7 L. Dassa Mechanical & Materials Engineering The MME group is in charge of engineering support for the maintenance of CERN facilities and the manufacturing of prototypes as required for CERN projects. This encompasses various activities such as the mechanical design and manufacturing, as well as the selection, the characterization and the treatments of surfaces and materials. The drawing tools that we are using are : AUTOCAD© Mechanical and CATIA ©

8 L. Dassa Metallic Productions : Niobium-Titanium, Niobium-Tin, Copper… Linac 4 CLIC RF Module

9 L. Dassa Metallic Productions : Copper, Niobium, Stainless Steel… RF Cavity Isolde RF Cavity SPL Cryo-Module LHC

10 L. Dassa Metallic Productions : Tungsten, Carbon Carbon, Glidcop, Macor… LHC Collimator Jaw PS Pick-Up

11 L. Dassa Composite Productions : Fiber Glass Epoxy BUSBAR Insulation Coil Spacer

12 L. Dassa Some project: cryostat for superconducting cables (1)

13 L. Dassa Some project: cryostat for superconducting cables (2)

14 L. Dassa Some project: standard and “special” pressure equipment He guard (SM18) Bolts able to hold up the pressure load Insert for cryostat (superconducting magnet test station) Bolts at cryo T, often with heavy load)

15 L. Dassa Common use at CERN for UHV: Bufab (ex Bulten) hexagon head screw, class A4-100, 316L stainless steel Bulten screws at CERN: LHC long straight section bolts nuts washer (machined in A4-100) threaded rod in A A4-100 used because the deformation during baking is lower than A4-80. It is better for sealing tightness.

16 L. Dassa Tightening test bench (1) Design Office request : - Development of a tightening test bench to evaluate the force applied on the structure versus the tightening torque; - Evaluation of the friction coefficients for several materials of screws and supports - Application range: M2 to M20 Collaboration: - Design of the setup : Design Office (MME) - Instrumentation (Force sensor, torquemeter) Measurements lab (MME) - Validation testsMeasurements lab (MME) - Validation resultsMME Courtesy of M. Guichard (EN-MME-EDM)

17 L. Dassa Theoretical Approach Γ : Tightening torque [N.m] F : Force obtained during tightening [N] D : Maximum diameter of the support [m] d : Nominal diameter[m] γ : Helix angle [rad] ρ : Friction angle [rad] p : Pitch [m] d 2 : Thread diameter [m] αa : Thread flank angle [rad] μ 1 : Thread friction coefficient μ 2 : Screw head friction coefficient Tightening test bench (2) Courtesy of M. Guichard (EN-MME-EDM)

18 L. Dassa Torquemeter ±0.2% Force sensor ±0.5% Screw Test bench Tightening test bench (3) Courtesy of M. Guichard (EN-MME-EDM)

19 L. Dassa Tightening test bench (4) Results Courtesy of M. Guichard (EN-MME-EDM)

20 L. Dassa LHC diodes: bolted joints characterisation (1) LHCDQDDP to to … Torque (Nm)5.510 ScrewM6x20M6x25 WashersFlat one in stainless steel 4 CuBe spring washers Length of engagement in the heat- sink (mm) 8.5Maxi 10 Courtesy of M. Guichard (EN-MME-EDM) GOALS : To verify the behavior of the bolted joints at warm/cold, including the spring washers; To check consistency with the expectations ; To verify the behavior of the big washers that preload the diode.

21 L. Dassa Base lineWith LoctiteAfter Loctite LHC diodes: bolted joints characterisation (2)

22 L. Dassa LHC diodes: bolted joints characterisation (3)

23 L. Dassa LHC diodes Bolted joints characterisation (4) In-situ bolted joints evaluation – Correlation with FEA r Heat sink Bolt M6x20 Bus-Bar Spring washers (assumed to be completely flat) z Location of the strain gagesContact bolt –bus bar zoom Courtesy of M. Guichard (EN-MME-EDM)

24 L. Dassa LHC diodes Bolted joints characterisation (5) The engagement length of the bolted joints (Heatsink / busbar) is very close to the design limit according to the VDI ; The initial compression force generated by the screw is equivalent to 7kN for 10Nm for a baseline configuration ; The assembly cycles and loctite  can degrade the compression force provided by the screws ; The loctite  can generate a very bad resistance contact ; The assembly of 4 M6 Spring washers in CuBe provide a spring effect up to 8kN ; For the baseline configuration (M6x25, 4 spring washers, 10Nm), the stress evolution with the thermal cycles is stable; Experimental results confirm the FEA calculation performed on the sub-systems. Courtesy of M. Guichard (EN-MME-EDM)

25 L. Dassa Discussion

26 L. Dassa PED compliance? “BUMAX 88 is the first bolt on the market with PMA approval (Particular Material Appraisal) under PED 97/23/EC.” Special order? Every Bumax 88? Material certificate? Questions for discussion (1) Courtesy of Bufab

27 L. Dassa Questions for discussion (2) High strength bolts: test at cryo T? test at high T? Radiation? Raw material (bars) in high strength stainless steel?? Exotic material for screws (Inconel, Titane – for experiment -, …) Courtesy of Bufab

28 L. Dassa Questions for discussion (3) Cryogenic tests: reports? High temperature tests: reports? Radiation performances? Tests? Effects on structure? On the new materials?

29 L. Dassa Magnetic permeability? Test reports? Questions for discussion (4) Courtesy of Bufab

30 L. Dassa Are you interested in special coatings? Molykote coating on bolts (issues with thickness? / some optimization? 10 cycles? Today after some cycle they are replaced) Kolsterising / Bodycote? Could you mark a set of screw with special CERN stamps? Which is the minimum amount of pieces? Questions for discussion (5)