1. Engineering Department ENEN Screwed solutions for the new tertiary collimator jaw assembly Federico Carra (CERN EN/MME) Geneva, 4 th September 2014 4th September 2014F. Carra– CERN / EN-MME1

2. Engineering Department ENEN  Engineering in the MME design office  Example of screwed assembly design: LHC tertiary collimator Outlook 4th September 2014F. Carra– CERN / EN-MME2

3. Engineering Department ENEN 10 Engineers in MME design office (mechanical, aeronautical, materials, …)  Project coordination  Calculations in pre-design and design phases  Analyses on components already installed in the accelerators  Diagnostics on device malfunctioning  R&D: materials, test organization and design, etc.  Engineering specifications, safety files, safety procedures Engineering at MME design office 4th September 2014F. Carra– CERN / EN-MME3

4. Engineering Department ENEN  Engineering in the MME design office  Example of screwed assembly design: LHC tertiary collimator Outlook 4th September 2014F. Carra– CERN / EN-MME4

5. Engineering Department ENEN  Beam-induced accidents represent one of the most dangerous and though less explored events for Accelerators.  Beam Intercepting Devices (BID) are inherently exposed to such events  LHC beam energy is 2 orders of magnitude above previous machines. Stored energy density is 3 orders of magnitude higher.  Novel, yet-to-characterize, composite materials are under development to meet these challenges.  New sophisticated and powerful Numerical Tools (Hydrocodes) are used to simulate accidental events. 4th September 2014F. Carra– CERN / EN-MME5 LHC Collimators: Context

6. Engineering Department ENEN 6 4th September 2014F. Carra– CERN / EN-MME Vacuum tank Jaws Actuation system Jaws  40µm surface flatness on 1m  10µm positioning accuracy  Heat load: up to 30 Kw

7. Engineering Department ENEN Tungsten (Inermet® IT180) TCTP collimator: brazed vs. screwed 4th September 2014F. Carra– CERN / EN-MME7  50 M4 stainless steel screws (A4-100 silver-coated) are used to fix tungsten blocks to the housing  2 options for the assembly housing/cooling circuit/stiffener:  Brazing with a silver alloy  Screwing with 54 M4 screws (A4-100 silver coated)  All the calculations of tightening torque and preload are done according the German Standard VDI2230 Brazing

8. Engineering Department ENEN TCTP collimator: brazed vs. screwed 4th September 2014F. Carra– CERN / EN-MME8 BRAZED  Good thermal contact between the components  No risk of relaxation at the interfaces in operation  Expensive and complicated procedure SCREWED  Simple and quick assembling  Cheap  Thermal contact dependent on the screw preload  Risk of stress relaxations at the interfaces, especially during bake-out cycles at 250 ˚C

9. Engineering Department ENEN Thermal contact at the interfaces 4th September 2014F. Carra– CERN / EN-MME9  In a screwed contact, the thermal conductance is a function of the pressure at the interface:  The higher the conductance, the lower the jaw maximum temperature in operation and the thermally-induced deformations!  With the pressure given by the M4 screws, the calculated conductance is 7000 W/m 2 K  A thermo-mechanical finite element analysis was necessary to understand if the conductance granted by the screws was high enough to guarantee temperatures and deformations within the component specification. Thermal conductance Contact pressure

10. Engineering Department ENEN Temperatures Deformations Conductance 7000 W/m 2 K Initial temperature: 27 ºC Flow rate inside cooling pipes: 5 l/min Bulk temperature of cooling water: 27 ºC Thermally induced deflection ~ 50  m; Deflection provoked by gravity ~ 25  m; Total deflection ~ 50 + 25 (worst case) = 75  m Specification: 100  m  OK! Thermo-mechanical behaviour The conductance theoretically achievable with the screws (7000 W/m 2 K) would be enough to guarantee temperatures and deformations during operation within the specification

11. Engineering Department ENEN Experimental conductance measurement  The conductance calculation was validated with experimental measurements performed by I. Leitao with an ad-hoc setup  The prototype produced contained 1 screwed jaw and 1 brazed  The screwed jaw has an acceptable conductance in every measured section  Surprisingly, the brazed jaw has a conductance not so much higher than the screwed one!

12. Engineering Department ENEN Could creep-induced deformations occur during bake-out (~ 250 ºC)?  Eq. stress on CuNi < 60 MPa  Eq. stress on Glidcop Al-15 < 100 MPa  No significant creep deformations expected on TCTP jaw components Copper OFE Copper OFS CuNi alloys Glidcop Creep Resistance Low High Zoom on Glidcop stiffener: stress under the head of a screw Orange area: equivalent stress comprised between 60 and 100 MPa Stress relaxation: FEM analysis 4th September 2014F. Carra– CERN / EN-MME12

13. Engineering Department ENEN  In case creep and stress relaxation occur, a decreasing in conductance is expected  To rule out creep, we performed complete 3 bake-out cycles (~6days at 250 ˚C), measuring the thermal conductance between pipes and jaw before and after the treatment Stress relaxation: experimental validation 4th September 2014F. Carra– CERN / EN-MME13  No negative effect has been observed!

14. Engineering Department ENEN 4th September 2014F. Carra– CERN / EN-MME14 Conclusions  Two different jaw designs were proposed for the new tertiary collimators: brazed and screwed  Numerical and analytical calculations, followed by experimental measurements, ruled out problems of unsufficient thermal conductance and creep resistance of the screwed assembly  The prototype produced features one brazed jaw and one screwed, and could potentially be installed in the LHC to prove the validity of the two solutions

15. Engineering Department ENEN Department of Mechanical and Aerospace Engineering (DIMEAS) F. Carra– CERN / EN-MME154th September 2014

16. Engineering Department ENEN 4th September 2014F. Carra– CERN / EN-MME16 Conclusions  MME design office engineers are involved in several phases of a component life (pre-design, design, installation, operation).  Analytical and/or empirical techniques are often adopted when studying problems that can be simplified to a certain extent.  For complex structures, implicit FEM codes like ANSYS are usually adopted to perform structural analyses (static, transient, modal, harmonic, …) as well as multiphysics calculations (e.g. thermo-structural, electro-thermal, etc.).  In some exceptional cases, involving material explosion, spallation, change of phase, high non-linearities, the study is performed with Hydrocodes like Autodyn or LSDyna.  An intense material R&D program is also pursued, in collaboration with other MME sections (MME/MM, mechanical laboratory, mechanical workshop), different CERN groups and departments, as well as external European partners, mainly in the frame of the Eucard collaboration (PoliTo, Kurchatov Institute, GSI, RHP, BrevettiBizz, EPFL, etc.).

17. Engineering Department ENEN Primary Collimator p e p Core Unavoidable losses Shower Beam propagation Impact parameter ≤ 1 mm Primary halo (p) p C-C Collimators are affected by intrinsic limitations which may ultimately limit LHC performances: Poor electrical conductivity (High RF impedance) Limited Radiation Hardness (Reduced Lifetime) Low-Z material (Limited Cleaning Efficiency) C-C Collimators are affected by intrinsic limitations which may ultimately limit LHC performances: Poor electrical conductivity (High RF impedance) Limited Radiation Hardness (Reduced Lifetime) Low-Z material (Limited Cleaning Efficiency) Absorber C-C WW Super- conducting magnets SC magnets and particle physics exp. Courtesy: R. Assmann Novel Materials for Collimators Absorber Phase II Collimator Secondary Collimator The collimation system must satisfy 2 main functions: Multi-stage Beam Cleaning, i.e. removing stray particles which would induce quenches in SC magnets. Machine Protection, i.e. shielding the other machine components from the catastrophic consequences of beam orbit errors. The collimation system must satisfy 2 main functions: Multi-stage Beam Cleaning, i.e. removing stray particles which would induce quenches in SC magnets. Machine Protection, i.e. shielding the other machine components from the catastrophic consequences of beam orbit errors. 4th September 2014F. Carra– CERN / EN-MME17