Thermal and Structural FEA simulations
of the CLIC Accelerating Structures.
4 April 2011
CLIC Test Module WG meeting
Tessa Charles
Monash University,
Australia
Accelerating Test Structures
CLIC Test Structure
• Simplified inner geometry
• No beam
• For thermal tests in June
2011
4 April 2011
CLIC Module WG – Tessa Charles
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Heat Load Calculations
Pulse Shape
4 April 2011
Operation
mode
Thermal
dissipation
to accel.
structure.
(W)
Mean
power in
the load
(W)
Mean
power
in the
beam (W)
Unloaded
(no beam)
410.6
357.6
no beam
Loaded
(with beam)
336.2
219.2
212.8
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Results - Thermal
Heat transfer coefficient: 5000 W/(m°C)
Ambient temp: 22°C
Mesh
Heat load
4 April 2011
Steady State solution
Transient solution
CLIC Module WG – Tessa Charles
4
Results - Structural
Von Mises Stress
• Maximum stress = 5.96 MPa
(yield of OFHC copper ≈ 200 MPa)
• Indication of where cracks may initiate
4 April 2011
CLIC Module WG – Tessa Charles
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Pulsed RF Heating
• Eddy currents induced by tangential magnetic fields heat the
structures surface.
• For CLIC, 32 MW of RF power deposited in 240 ns.
• Create a thermal shock wave as heat travels faster than material
can expand
• Repetition rate of 50 Hz, can lead to thermal fatigue
Surface Temperature Rise due to thermal shock:
where P = thermal flux,
ρ = density, c= specific heat
p
t_p = pulse length,
k = thermal conductivity
2P
T(t) 
t
kc
4 April 2011
CLIC Module WG – Tessa Charles
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Pulsed RF Heating
Skin Depth:

1
0f rep
 0.599 m.
where μ0 is the magnetic permeability,
σ is the conductivity, and
frep is the repetition frequency
Diffusion length:
Dd 
4 April 2011
k tp
 c
 5.23 m.
where k is the thermal conductivity and
tp is the pulse length,
ρ is the resistivity, and
c is the specific heat capacity
CLIC Module WG – Tessa Charles
7
Results - Detailed Transient
• Only inner iris modelled to
observe surface effect
• Very fine mesh of the order of
1μm
• Time step of the order of 10 ns.
(Shape is of interest)
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CLIC Module WG – Tessa Charles
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Comparison with theory
2P
T(t) 
tp
kc
From previous
slides
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CLIC Module WG – Tessa Charles
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Conclusions
• Water cooling sufficient for removal of bulk material
heating
• 130 s until steady state reached for test structure.
• Confirmed that ANSYS is capable of modelling detailed
transient solution of pulsed surface heating
• ... and identified max. surface temperature as possible
problem
4 April 2011
CLIC Module WG – Tessa Charles
10
Further Work - final year engineering project
• Flow induced vibrations study
– Using FLUENT to determine the conditions under which vortex shedding occurs.
– Studying a range of Re numbers to hopefully place a limit on the mass flow rate.
• Develop a numerical model to describe the thermal shock
wave phenomenon using Finite Element Analysis (FEA).
– i) Set up a three dimensional model of the electromagnetic field distribution within
the accelerating structure. (HFSS)
– ii) Using this simulation, calculate the heat induced by Ohmic heating at the cavity
surface
– iii) Set up a model using a transient-structural solver (ANSYS 13) to describe the
thermal shock wave as it travels through the structure.
• Compare simulations with results taken experimentally.
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Additional Remarks
• Are more/different simulations required?
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Acknowledgements
Many thanks to...
•
•
•
•
Germana Riddone (CERN)
David Wang (AS)
Rohan Dowd (AS)
Mark Boland and Roger Rassool (ACAS)
Thank you for your attention 
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CLIC Module WG – Tessa Charles
13
Back up slide
Eigenmode analysis of TD26 structure
Preliminary Results
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CLIC Module WG – Tessa Charles
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