A. Bertarelli

1
CERN European Organization for Nuclear Research
Mechanical Engineering and Thermo-mechanical
Analysis of LHC Collimators Alessandro
Bertarelli TS Materials and Mechanical
Engineering Group External Review of LHC
Collimator Project 01 July 2004
2
OUTLINE

• Project Requirements
• Design strategy
• Technical design
• Thermal and Mechanical Calculations
• Conclusions

3
PROJECT REQUIREMENTS

• Functional specification (Mechanical aspects)
• High absorbed heat load (up to 32 kW)
• Very high precision (25mm on 1200mm)
• High robustness in accident cases (up to 700ºC)
• Low-Z, high conductivity materials for jaw
  (carbon based)
• Limited jaw temperature (lt50º C) for outgassing
  reasons
• Easy maintenance
• Schedule (see M. Mayers talk for details)
• Design Activity started in September 2003
• First full prototype TCS by May 2004

4
DESIGN STRATEGY

• How to meet the challenging requirements ?
• Highest priority to Secondary Collimators (TCS)
• Contribution of many experts
• Wide exploitation of LEP experience
• In-depth calculations carried out from the early
  stages of development (concurrent design)
• Mix of traditional and edge technologies.
• Advanced Materials (C/C composites, GlidCop ).
• Specific tests to validate most critical
  technologies (S. Calatronis talk)

5
TECHNICAL DESIGN

• Main Features (TCS design)
• Multi-DoF internal alignment system.
• Monolithic jaw (1200mm) clamped to the support.
• Decoupling and compensation of thermal
  deformations.
• Cooling system.
• RF contacts for low impedance.
• Actuation system (2 step-motors per jaw).
• External alignment system and plug-in
• Electronic controls

6
TECHNICAL DESIGN Mechanical Assembly
Overall length 1480mm Tank width 260mm
Vacuum Tank
Actuation system
Beam axis
Main support and plug-in
External adjustment motor
7
TECHNICAL DESIGN Collimator Cross-section (1/2)
Jaw stroke 30/-5 mm
Jaw (25x80x1200 mm)
Support Bar
Cooling Pipes
Clamping springs
Bellow
Stepper Motor
Return Spring
8
TECHNICAL DESIGN Collimator Bloc
1. Jaws in C/C or graphite 2. Cooling Cu-pipes
and plate pressed against the jaw, brazed to the
bar. 3. GlidCop support bar and clamping plates

• Low thermal contact resistance (P35 bar)
• Differential thermal expansion allowed
• Deformations minimized (compensation)

1
2
3
9
TECHNICAL DESIGN Actuating System
1. Jaw actuated by 2 stepper-motors via a roller
screw (10 mm/step) 2. Return spring for semi -
automatic pullback and play recovery 3.
Rack-pinion system to prevent misalignments 4.
Vertical sliding of the jaw surface (? 10mm)
3
2
1
2
3
1
10
TECHNICAL DESIGN Cooling System

• Jaw cooled by 2 Ø6 OFE-Cu pipes (3 loops each)
• Outer section squared (?9) to allow brazing to
  internal and external plates
• Water from general cooling circuit (Inlet temp.
  up to 27ºC)
• Water flow 5 l/min (20 l/min per collimator)
  leading to a 3 m/s velocity

11
THERMOMECHANICAL ANALYSIS

• Main problems to tackle in analysis and design
• How to evacuate heat loads?
• How to join graphite jaw and metal support?
• How to keep thermal deformations to a minimum?

12
THERMOMECHANICAL ANALYSIS

• Extensive analytical and numerical calculations.
• Semi-analytical models for Thermal contact
  resistance, Convection, Thermal bending
• Many FE models (ANSYS) of the TCS were studied
• 2- and 3-dimensional
• Different materials (C/C, C, Cu, Steel,
  Glidcop)
• Input thermal load imported from FLUKA
  simulations
• Different load cases (nominal, accident,
  transient)
• Complex boundary conditions

13
THERMOMECHANICAL CALCULATIONS
How to evacuate heat and allow free expansion
P
RMS Roughness Rq
kG
EG
kCu
Mean Asperity Slope Da
P

• Less than 1 of the interface surfaces is usually
  in contact
• Pressure is necessary to increase the effective
  contact surface
• Thermal conductance might be evaluated
  analytically

14
THERMOMECHANICAL CALCULATIONS
How to minimize thermal deformations
M1
M2
DT
M3
uiaDT/B duL2/8
the principle of compensation is used
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THERMOMECHANICAL CALCULATIONS
FEM Model for 3-D analysis
Convection (12360W/m2/K) inlet temp. (27ºC)
Temperature - dependent properties (when
available)
Geom. B.C. Hinged Free expansion
Deposited Heat Power (W/m3)
Contact elem. (friction therm. Conductance)
Preloaded Springs (5 bar)
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THERMOMECHANICAL CALCULATIONS

• Remarks on jaw materials
• Several materials were analyzed for the jaws
• Snecma NB31 3-d C/C (Y max X min)
• Snecma NB31 3-d C/C (Z max Y min)
• SGL C1001 2-d C/C
• Tatsuno AC150 2-d C/C
• SGL R4550 isotropic graphite
• Out of these only AC150 and R4550 were retained
  since they present the best compromise in terms
  of deformations, strength and availability.

17
THERMOMECHANICAL CALCULATIONS
Thermal analysis Nominal Conditions 7 TeV 8e10
p/s Steady-state (p5 bar)
2-D C/C AC150 TMax 47ºC
Graphite R4550 TMax 51ºC
18
THERMOMECHANICAL CALCULATIONS
Displacement analysis Nominal Conditions 7 TeV
8e10 p/s Steady-state
2-D C/C AC150 dMax20mm
Graphite R4550 dMax14mm
19
THERMOMECHANICAL CALCULATIONS
Displacement analysis Nominal Conditions 7 TeV
4e11 p/s Transient (after 10s) To be confirmed
2-D C/C AC150 dMax30mm
Graphite R4550 dMax47mm
20
THERMOMECHANICAL CALCULATIONS
Stress Analysis Nominal Conditions 7 TeV 8e10 p/s
steady-state
2-D C/C AC150 sMax7.8MPa
Graphite R4550 sMax5.8MPa
21
THERMOMECHANICAL CALCULATIONS
Stress Analysis Accident case 7 TeV 9.1e11 p (200
ns)
AC150 Tmax 724º R4550 Tmax 698º
Courtesy A. Dallocchio
22
THERMOMECHANICAL CALCULATIONS
Load case summary
Notes Rsadm(1-n)/Ea
23
CONCLUSIONS

• Based on the given requirements, technical layout
  is a mix between traditional and new solutions
• Mechanical design was finalized
• Feasibility confirmed by prototype manufacturing
  
• Extensive thermo-mechanical analyses results
  predict that tough specification should be
  attained within reasonable limits,
• provided available data are correct (material
  characterization results are forthcoming)
• and new Fluka simulations confirm previous
  loads.
• In nominal conditions stresses are well below the
  limits.
• Special attention must be given to accident
  scenarios, where stresses come close to
  admissible limits (see O. Aberle talk)