CRYOMODULES ENGINEERING DESIGN
MAX School
MAX cryomodule
SPL cryomodule
Patricia Duchesne
IPNO – Accelerator Division
Institut de Physique Nucléaire d’Orsay
ESS cryomodule
SPIRAL2 cryomodule
MAX School
P. 1
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 CRYOGENIC SCHEME OF A CRYOMODULE
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CONCLUSION
2013/10/02
MAX School
P. 2
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
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MAX School
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DESIGN OF A CRYOMODULE
A cryomodule is an unit cell of an accelerator that contains some
Superconducting Radio Frequency (SRF) cavities and all the components
required to their operation at cryogenic temperatures.
INTRODUCTION
Warm quadrupole
Cryomodule
(3 cavities =0.65 )
SPL Layout (2010): segmented architecture
Cryomodule
(8 cavities =1 )
SPL Cryomodule (8 cavities =1)
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MAX School
P. 4
DESIGN OF A CRYOMODULE
A cryomodule is:
A part of an accelerating section
A part of an overall cryogenic system
INTRODUCTION
Type of cavities, number of cavities,
focusing elements:
The accelerator design determines in part
the composition of the cryomodule
Independent cryogenic subsystems or
connected to each other:
The overall cryogenic system impacts on
the segmentation of the accelerator and
therefore on the cryomodule
The design of a cryomodule depends on several parameters:
 The accelerator design (accelerating and guide components, sequence)
 The overall cryogenic system (independent subsystems or connected each other)
 The expected performance of the accelerator (reliability, availability ...)
 The cost
Manufacturing cost: high filling factor (long cryomodule, short interconnections)
Operating cost:  static heat losses (long cryomodules cryogenically connected)
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MAX School
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CRYOMODULES/CRYOSTATS, SEVERAL EXAMPLES
GANIL-SPIRAL2 FRANCE
ESS-LUND-SWEDEN
INTRODUCTION
Beginning in 2019
DESY- HAMBURG-GERMANY
J-PARC-TOKAI-JAPAN
SNS, TENNESSEE-USA
LHC – CERN-SWITZERLAND
CEBAF, J-LAB-VIRGINIA-USA
2013/10/02
MAX School
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CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
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MAX School
P. 7
BASIC FUNCTIONS
BASIC FUNCTIONS
 A cryogenic environment for the cold mass
Cryogenic distribution (piping, phase separator, valves): He coolant (liquid or gas)
at required temperatures
o The vessels of the cavities/magnets are filled with liquid helium at 4K or
lower temperature.
o The active thermal shield can be cooled with helium gas
o The magnetic shield
o The power coupler
 Thermal insulation (shield, vacuum and superinsulation) against all sources of heat
transfer from room temperature to cryogenic temperature
o Heat conduction
o Heat transfer by convection
o Thermal radiation
 Supporting and positioning components
o Structural support of the cold mass
o Precise alignment of the cavities regarding the beam and reproducibility
with thermal cycles
 Interface between the cold mass and the room temperature
o Connection points for integrated systems: current, RF, instrumentation
and cryogenics
 Magnetic protection against the magnetic field from the earth and other sources
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CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
2013/10/02
MAX School
P. 9
MAIN COMPONENTS
 Vacuum vessel


Thermal Insulation
Interface
Vacuum vessel
Cryogenic piping
String of cavities
 Supporting components
MAIN COMPONENTS

Supporting and positioning
 Thermal shields

Thermal Insulation
 Cryogenic piping

Cryogenic environment
1,80m
 Magnetic shield

Magnetic protection
Thermal shield
Magnetic shield
Supporting components
ESS Spoke Cryomodule
 Cold mass (cavities, magnets)
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COLD MASS (CAVITIES, MAGNETS)
String of dressed superconducting RF cavities (equipped with their helium vessel and
their ancillaries) and possibly presence of superconducting magnets of focalization
SC Cavity: Pure niobium, Helium vessel: titanium, stainless steel
 Assembly string: ultra cleanliness required for the internal walls of the cavity and those of the
MAIN COMPONENTS
coupler  The string is prepared in clean room with mounting of the power couplers, warm cold
transitions and vacuum valves at the extremities
 Cavity: elliptical, spoke, quarter-wave, and half-wave resonators
Warm cold transition
Inter cavity bellows
Helium vessel
Vacuum valve
Cold Tuning system
Power coupler
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ESS String of spoke cavities
MAX School
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MAGNETIC SHIELD
Providing a protection against the earth magnetic field and fields from other sources
(ex: magnet stray fields)
AMUMETAL (nickel-iron alloys) at room temperature, CRYOPERM at low temperatures
MAIN COMPONENTS
 Around the cavity (shield at low temperature)
To be efficient, the shield has to be cooled before the critical temperature of the cavity
(superconductivity)
 Around all the components of the vacuum vessel (shield at room temperature)
Magnetic shield with a cooling
system between two walls
(Cryoperm):
magnetic shield (Cryoperm)
around each cavity:
SPL Short Test Cryomodule
ESS Spoke Cryomodule
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CRYOGENIC PIPING
Pipes providing cryogenic fluids at different temperatures
Stainless steel, aluminium or copper
 Cryogenic piping depends on the cryogenic distribution system of the accelerator
(see § Cryogenic scheme of a cryomodule):
MAIN COMPONENTS
- Cryomodule cryogenically connected to form a cryo-string (minimizing the number of cryogenic feeds)
 Cooling and return pipes integrated into the cryomodule
- Cryomodule cryogenically independent  Each cryomodule is connected to the Cryogenic Transfer
Line (CTL) via a valve box.
 Cryogenic piping provides cryogenic fluids to:
- Thermal shield
- Magnetic shield
- Power coupler
- Warm to cold transition
- Cavity
Cryogenic
valves
Biphasic tube
Thermal
shield tube
Warm to cold
transition pipe
Magnetic
shield tube
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MAX School
Coupler
tube
P. 13
THERMAL SHIELDS
Active thermal shield at intermediate temperature (50-80K)
Passive thermal shield (Multi Layer Insulation)
 To minimize the radiation heat transfer
 Metallic shield: aluminium or copper actively cooled at 50K-80K
Its design is strongly conditioned by the problematic of thermal contractions and of assembly
MAIN COMPONENTS
 MLI (Multi Layer Insulation): composed of some reflective layers (aluminium) alternated of
some insulating spacers (mylar) placed on:
the surface of the thermal shield (~ 30 layers)
the surface of the components at lower temperatures (~ 10 layers)
Thermal shield
MLI
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SUPPORTING COMPONENTS
Supports maintaining all the components in the vacuum vessel
Resin, composite, Titanium alloy, ...
 Stiff and stable over the lifetime: Support the weight of the components and maintain the
good alignment of the cold mass
MAIN COMPONENTS
 Warm to cold transitions: limit conduction heat transfer
Tie rods
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VACUUM VESSEL
Metallic vessel containing the insulating vacuum to minimize convection
heat transfer
Carbon steel, stainless steel, aluminium (pressure requirements, magnetic shield potential, the cost ...)
 A tight structure: guarantee 10-7 bar inside
the vacuum level
MAIN COMPONENTS
 A rigid structure: No risk of buckling
 It must provide:
−
−
−
−
−
Floor fixing supports
Ports for coupler, cryogenic piping, instrumentation ...
Attachment points of the cold mass
Supports for alignment
...
Instrumentation port
Vacuum vessel
Cover ends
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Attachment point
of the cavity
MAX School
Safety valve
coupler port
Optical
alignment
Supports
P. 16
VACUUM VESSEL
Examples of vacuum vessel studied at IPNO:
ESS Spoke Cryomodule:
MAX Spoke Cryomodule:
SPIRAL2 Cryomodule B:
1,3m
1,2m
MAIN COMPONENTS
2,8m
1,9m
2,8m
ESS Elliptical Cryomodule:
1,2m
~ 6,5m
1,16m
SPL Short test Cryomodule:
0,8m
2013/10/02
~ 7m
MAX School
P. 17
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 CRYOGENIC SCHEME OF A CRYOMODULE
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
2013/10/02
MAX School
P. 18
CRYOGENIC SCHEME OF A CRYOMODULE
COOLING MODES
SRF cavities are generally cooled
with an isothermal saturated bath
(equilibrium vapour and liquid phases):
- T = 4.2K and P = 1 bar
- T < 2.1K and P < 30 mbar
Stable pressures, limitation of
pressure fluctuations that have an
impact on the cavity frequency
A bath at T< 4.2K is generated by
isenthalpic expansion, through JouleThomson valves (pumping)
Accelerator magnets are often cooled
with subcooled liquid:
 Surfaces completely covered with
liquid, stabilization of superconductors
2013/10/02
Helium phase diagram
Superfluid
Pressurized
Helium
Helium I
Saturated
Helium I
Pressurized
Helium II
Saturated
Helium II
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P. 19
P&ID (Piping and Instrumentation Diagram)
CRYOGENIC SCHEME OF A CRYOMODULE
Example of P&ID of ESS spoke cryomodule:
Cryogenic Transfer Line (CTL)
Helium supply and
return pipes
19.5 bar, 40K
3 bar, 4.5K
31 mbar
Cold box
Cryogenic distribution
(valves) and Heat
exchanger
Cryomodule
Cool down lines
Filling lines
Helium gas return lines
helium gas line
String of
cavities at 2K
• Safety elements (burst disk,
pressure safety valves),
• Control valves
• Vacuum circuit
• Process diagnostics, Sensors
2013/10/02
Saturated helium II
bath at 2K in the phase
separator pipe
MAX School
P. 20
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
2013/10/02
MAX School
P. 21
PHYSICAL MECHANISMS OF HEAT LOSS
Insulation
vacuum
293K
40K - 80K
RF cavities
2K-4K
 Convection heat transfer:
- Negligible with a good insulating vacuum
into the vessel (< 10-3mbar)
Coupler
THERMAL ASPECTS
 Radiation heat transfer:
- The most important (varies in T4)
Supports
Conduction heat transfer
Radiation heat transfer
 Conduction heat transfer:
- Penetrations from room temperature
(power coupler, instrumentation…)
- Mechanical supports
Identify all heat losses:
 Impact on the choices of materials and geometric shapes
 Total static heat load (in relation to the cryogenic fluid consumption).
Dynamic heat load (operation of the cavity and power coupler):
• Pulsed operation: Pstatic >> Pdynam  get a good thermal insulation
• Continuous wave operation (CW): Pdynam>>Pstatic  focus on the problems of heating
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HEAT CONDUCTION
Transfer by heat conduction  All mechanical supports
Heat load (W) by conduction is given by the Fourier law:
Q
T
A
Q  
L
 λ( T).dT
0
THERMAL ASPECTS
T
1
A
L
l(T)
300 K
4K
T2
: section (m²)
: length (m)
: thermal conductivity (W/mK-1)
L
x
Calculated from:
Q  constant
AISI 304L
To limit Q while guaranteeing mechanical strength:
Q1
Q2 80 K
300 K
4K
 Geometry: A, L
L2
 Material with low conductivity l(T)
L1
 Thermal intercepts at intermediate temperatures:
AISI 304L
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HEAT CONDUCTION
Example: Support rods between the helium vessel and the vacuum vessel
Material: AISI 304L
Diameter D: 8mm
Length L: 665mm
4

A
 Without any thermal intercept: Q  
λ( T).dT  0.23W by rod
L 300
L
300K
THERMAL ASPECTS
 With a thermal intercept at T=80K:
80

4

A

   A λ( T).dT
Q


λ(
T).dT
Q
80
4
L  x  300
x 80
The optimal position x can be defined by minimizing the power required to dissipate
the heat taking into account Carnot efficiency

with Ẇ: Required work for refrigerator to
Tc
Q



Ideal Carnot cycle:
dissipate Q at Tc (Tw=300K)
Tw  Tc
W
220 
296 
==> W  W 80  W 4 
 Q80 
 Q4
80
4
a1
a
x
==> W   
 2  Optimum: x/L = 0.65
x
 L  1 x
L
L


Q
80  0.59W Q4  0.04W
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MAX School
x
80K
With a thermal intercept at 80K
Without any thermal intercept
0
4K
0.65
Ẇ=17.2W against Ẇ=4.8W
P. 24
HEAT CONDUCTION
THERMAL ASPECTS
Example: Support rods of SPIRAL2 CRYOMODULE B
Lateral rods between the
cavity and the vacuum
vessel, thermalized at 80K
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Copper tresses between the
rods and the thermal shield
MAX School
P. 25
HEAT CONDUCTION
Example: Support posts of cryomodules type TTF (XFEL, ILC)
Heat loads:
 A
Q
L
T2
 λ( T).dT

Q
70  9.6W

Q
4.5  0.84W

Q
1.8  0.04W
T1
THERMAL ASPECTS
Estimation of the refrigerator load:
Carnot efficiency
 W
 W
 W
  93.3W
W
70
4.5
1.8
Without thermal intercepts:
  2.79W
Q
Aluminium disk connected to
the thermal shield at 70K
300K
L1=27mm
70K
Tube G-11 thickness 2.2mm, ext=300mm
L2=37mm
L3=10mm
  462.2W
W
4,5K
Aluminium disk connected to
the thermal shield at 4,5K
1,8K
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P. 26
HEAT RADIATION
Transfer by heat radiation All surfaces of the components
Heat load (W) by radiation is given by the Stefan-Boltzmann law:
THERMAL ASPECTS
Q12   .F12.S1.(T14  T24 )

S1
F12
: Stefan Boltzmann constant (=5.67x10-8 W/m²K-4)
: Surface area (m²)
: View factor (depends on geometry and emissivity)
Where Q12 is the thermal radiation power from surface 1 to surface 2.
Q12
F12 
Infinite coaxial cylinders:
1 S1
(simplified model of a thermal

1 S 2
shield with the vacuum vessel)
1
 1

  1
 2 
To limit Q12 :
 Material with low emissivity  (shiny surfaces...)
 Active thermal shield at intermediate temperature
 Passive thermal shield MLI (MultiLayer superInsulation)
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HEAT RADIATION
Example: Heat load by radiation with or without thermal shields
Vacuum vessel in stainless steel:
Diameter = 0.8 m
 = 0.2
T° = 293K
Cold mass (string of cavities):
Diameter = 0.5 m
 = 0.1
T° = 2K
THERMAL ASPECTS
 Without any shield:
Q cold mass  53W
 Active aluminum thermal shield:
Q thermalshield  68W
Q
 0.2W
Diameter = 0.7 m
 = 0.1
T° = 75K
cold mass
 MLI layers around active aluminium thermal shield:
30 MLI layers from 293K: 1.5W/m²
Q thermalshield  3.3W
Q
 0.2W
cold mass
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HEAT RADIATION
Example: Thermal shields of the Cryomodule B – SPIRAL2
THERMAL ASPECTS
MLI placed on the magnetic shields
of each cavity, piping and bellows
MLI placed on the thermal shield
Active thermal shield
in copper
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MAX School
P. 29
EVALUATION OF THE STATIC HEAT LOAD
From the heat load budget  cryogenic fluids consumption
(dimensioning of the cryogenic plant)
Example: Heat load budget of a cryomodule
Static heat load at 4K:
•Helium port
Static heat load at 50K:
Rod
THERMAL ASPECTS
•Thermal shield
•Warm to cold transition
293K
50K
Cavity
Warm to cold
transition
Static heat load at 4K:
Helium vessel
4K
•Warm to cold transition
Thermal shield
•Power coupler
•Supporting system
Vacuum vessel
Static heat load at 50K:
•Supporting system
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EXAMPLES OF THE STATIC HEAT LOAD
ESS Spoke Cryomodule (in progress)
Cryomodule B – SPIRAL2
Static loads at 80K
[W]
THERMAL ASPECTS
Components
Static loads at 4K
[W]
Thermal shield
46.7
0.42
Supporting system
(rods)
3.93
2.55
Warm to cold
transitions
1.67
1.54
Two power couplers
10
1.5
Two cold tuning
system
1.07
0.16
Instrumentation
0.3
2.30
Total
64
8.5
Components
Static
loads at
50K [W]
Static
loads at 2K
[W]
Thermal shield
10
0.4
Supporting system (rods)
4
0.2
Warm to cold transitions
6
0.4
Safety equipement
4.1
0.25
Two power couplers
-
2.
Control valves
3
1.5
Instrumentation
8
0.2
Total
35
5.
MAX Spoke Cryomodule (in progress)
Components
Static
loads at
70K [W]
Static
loads at
10K [W]
Static
loads at
2K [W]
Thermal shield
<30
-
0.2
Space frame
16
1
<0.1
Warm to cold
transitions
4.34
-
0.2
Safety equipement
<2.
-
0.1
Two power couplers
<35
<7
<2.1
Instrumentation
<5
Total
<92
Cryomodule Type TTF
Static loads at
40/80K [W]
Total
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70
Static loads at
4K [W]
13
Static heat
loads at 2K
3.5
MAX School
0.5
<8
<3.2
P. 31
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
2013/10/02
MAX School
P. 32
MECHANICAL STRENGTH
Gravity: 1g
MECHANICAL ASPECTS
 Temperature field
• Thermal contractions
• Thermal stresses
Patm
Patm
 External pressure
50K
293K
Cavities
2K or 4K
 Gravity
• Weight of the components
Vacuum
Thermal shield
Patm
Vacuum vessel
Patm
Impact on the alignment and the stability of the components
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P. 33
TEMPERATURE FIELD
Temperature field in an assembly  Thermal contractions and stresses
2-4K
MECHANICAL ASPECTS
After the cool down,
the temperature field in
a cryomodule:
50-80K
300K
String of cavities
Thermal shield
 Some thermal contractions appear on all components:
 With different temperatures String of cavities at 2/4K: niobium, titanium, stainless steel...
Thermal shields at 50/80K: copper, aluminium
 With different materials
Cryogenic lines from 2K to 300K: stainless steel, aluminium...
Supports from 2K to 300K
 Theses contractions can create some high thermal stresses.
Solving problem of stresses will depend on the type of connection between the components
according to their function:
- Supporting,
- Transferring cryo fluid
- Vacuum circuit
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P. 34
THERMAL CONTRACTIONS AND STRESSES
How to estimate the thermal contractions and stresses?
Thermal contractions:
T1
 A rod:
MECHANICAL ASPECTS
DL = a . L . DT
L
a : Thermal expansion coefficient (1/K or 1/°C)
L : Characteristic length (m)
DT : Difference between final and initial temperatures (K or °C)
T1
 A tube:
DL
T2
Thermal expansions of different materials DL/L:
R
DR
DR = a . R . DT
T2
Thermal stresses:
If a tensile force F is applied to extend the length to the
initial length:
According to the Hooke Law:

F
DL
E
 E  a  D
S
L
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P. 35
THERMAL CONTRACTIONS AND STRESSES
Limiting the thermal stresses  according to the type of connections
- For supporting,
- For transferring cryo fluid
- For the vacuum circuit

F
DL
E
 E  a  D
S
L
MECHANICAL ASPECTS
 Material with low expansion coefficient: a
Ex: Resins, composites, TiA6V
Bellows
 Material with low Young modulus: E
Ex: Resins, composites
 Geometry:  Flexibility
Ex: compensator bellows, curved tube...
 Boundary conditions: Release some
degrees of freedom
Ex: Rotary joint, slide link
 Material with high Re (yield stress)
or Rm (Ultimate stress)
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Curved tube (lyre)
MAX School
P. 36
THERMAL CONTRACTIONS AND STRESSES
Example: Support rod between the helium vessel and the vacuum vessel
1.
Temperature profile in the rod:
T
A
Q  
x

A
λ( T).dT  
L
MECHANICAL ASPECTS
T1
Helium
vessel
T
T2
 λ( T).dT  Cst
300 K
4K
T1
0
2.
Vacuum
vessel
L
x
Contraction of the rod:
Cutting the rod in several sections, each defined by an average temperature:
DL 
3.

DLi 
L
293
i
 LTi 
For L=400mm:
Contraction of the helium vessel:
For R=150mm:
DR = a . R . DT
4.
AISI 304L:
G10:
TIA6V:
DL = 0.67 mm
DL = 0.47 mm
DL = 0.36 mm
AISI 304L: DR = 0.38 mm
Titanium: DR = 0.19 mm
Thermal stress in the rod:
D L  DR
  E   E 
L293
2013/10/02
(Helium vessel and vacuum vessel
are supposed infinitely rigid)
For Helium vessel AISI 304L:
Rod in AISI 304L :
 = 525 MPa
Rod in TIA6V:
 = 200 MPa
MAX School
P. 37
THERMAL CONTRACTIONS AND STRESSES
Example: Support posts of MAX cryomodule
Complex shape  FEM analysis (behaviour during cool down)
1.
Cavity Sliders
Displacements at 2K – Stationary state:
MECHANICAL ASPECTS
~ 3K
DZ
~ 80K
~ 295K
2.
~ 10K
Invar Rods
Table Slider
DZ
DX : 0.1 mm
DX : 0.4 mm
DX : 3,5 mm
Fixed Point
Mobile Point
Transient temperature gradients during the cooling down:
Non uniform temperature of the table during the
cooling down due to the non-balanced flow in the
table cooling tubes
80K
150K
300K
Transient
state
Stationary
state
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DT max
dX
dY
dZ
 V.M.
70 K (150-80)
3,4 mm
2,7 mm
1 mm
43 MPa
0 (80-80)
3,4 mm
1,6 mm
1 mm
50 MPa
P. 38
EXTERNAL PRESSURE
The external pressure generates on the walls of the vacuum vessel:
 Some deformations  Risk of misalignment
 Some compressive stresses  Risk of buckling
MECHANICAL ASPECTS
Each country has an applicable construction standard norm for the pressure vessels:
Requirements for the design, the materials, the fabrication, the control tests.
Ex: CODAP (France), European norm EN 13445, ASME(United States).
Patm
P=0
In the CODAP:
• Classification of the pressure vessels according to the volume, the maximum allowable
pressure and the nature of fluid.
• A vacuum vessel does not fall into a risk category but the design and the fabrication
follows the rules.
Theses requirements are applicable for the design of: the vacuum vessel, the nozzles, the flanges and the
bellows.
Determine the critical buckling pressure:
 For simple shapes:
• Using of design by formulae (CODAP, European norm) with a safety factor (takes into
account the manufacturing defects: geometry, materials)
• Analytical formulae (Roark) without safety factor
 For more complex shapes:
• Finite Element Model analysis
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P. 39
EXTERNAL PRESSURE
Example: unstiffened cylindrical vacuum vessel
Material: Steel P235GH NF EN 10028-2
External diameter De: 800mm
Length L: 6500mm
Thickness: 10mm
L
De
MECHANICAL ASPECTS
 CODAP: Calculation of the maximal allowable pressure
Pa 
4 B
K
3 De / e
K=1
: for normal operation
K=1.35 : for exceptional operation
- From a chart, determine the coefficient A = f(
L De
)  A  0.0002
,
De
e
- From a chart, determine the coefficient B = f(A, material, T°)  B  20 ( MPa)
Pa = 0,33 MPa
 Roark Formulae: Calculation of the critical buckling pressure
E  e2  1  e2
Pcrit  0,807
4 

L  R  1  2  R 2
(Formulae available for short tube)
Pcrit = 1,04 MPa
Safety factor ~ 3: Pcrit (Roark) = 3,15 x Pa (CODAP)
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P. 40
EXTERNAL PRESSURE
Example: SPL Short Test Cryomodule
Top cover
Material: Steel type P235GH
External diameter De: 800mm
Length L: 7000mm
Thickness: 10mm (bottom) / 6mm (top)
Flat flanges + O-ring
Complex shape  FEM analysis
Bottom part
MECHANICAL ASPECTS
 Linear buckling
SPL Cryomodule (last version)
Pcrit=23 bars (no safety factor)
 Extended study: Non linear buckling
• Elasto-plastic material
• Introduction of a geometrical defect
Elastic material
Elasto-plastic material
Non linear buckling:
Pcrit=8 bars
Linear buckling:
Pcrit=42 bars
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SPL cryomodule (old version)
MAX School
Buckling
P. 41
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
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P. 42
DIFFERENT CONCEPTS OF SUPPORTING
All structural supports of the components inside the vacuum vessel (cavities, shields...)
DIFFERENT CONCEPTS OF SUPPORTING
Whatever the type of support, the required functions are:
 To be a transition from the room
temperature to a low temperature
Limit the conduction heat transfers
Thin and long structure
Low conductivity material
 Supporting the components
 Position accuracy and preserving
the stability of the cold mass
Have a sufficient stiffness
Limit thermal contractions and stresses
Thick and massive structure
The mechanical design of the supports depends on 2 technical contradictions
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P. 43
DIFFERENT CONCEPTS OF SUPPORTING
 Tie rods
 Compressive posts
Vacuum vessel
 GRP with support posts
Vacuum vessel
Tie rods
Support posts
DIFFERENT CONCEPTS OF SUPPORTING
Vacuum vessel
Cold mass
Cold mass
Gas
Return
Pipe
Cold
mass
Compressive posts
 Space frame
 Others ...
Vacuum vessel
The choice depends on:
Tie rods
Cold mass
Pad supports
Spaceframe
• Assembly methods
• Alignment strategy (warm / cold / inside / outside)
• Cold mass weight (LHC)
• Length of the string of cavities
• Cryogenic distribution system (large GRP)
• Team member’s experience
•...
 There is no only one solution...
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P. 44
DIFFERENT CONCEPTS OF SUPPORTING
TIE RODS
 Using of the antagonist rods
• Preservation of the alignment in the plane formed by the
rods: The rods have the same thermal contraction
• Limitation of thermal stresses: the rod does not undergo
the thermal contraction of the cold mass
• Longer supports: Limit the conduction heat transfers
Vacuum vessel
Identical DL
Cold mass
 Join the rods to the vacuum vessel
Possibility to align after cooling down
Example: Cryomodule B - SPIRAL2
Antagonist rods in horizontal
o To adjust lateral alignment
o To maintain the lateral alignment of the cavity
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Vertical rods
o To support the weight
o Vertical displacement of the
cavity to anticipate for alignment
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P. 45
COMPRESSIVE POSTS
DIFFERENT CONCEPTS OF SUPPORTING
 Using of some pad supports (with table)
• The alignment of the string of cavities is realized outside the vacuum vessel
• The alignment is then realized by adjusting the vacuum vessel with an
external referential (transfer beam axis)
Vacuum vessel
Cold mass
 Use sliding supports and invar rod
• The thermal contractions of the table is not transmitted to the cavity
• Longitudinal position of the cavity is fixed by the invar rod
Pad supports
Example: MAX Cryomodule for spoke cavities
o To adjust alignment
Sliding support o To maintain alignment
Invar rod
o To maintain longitudinal
alignment of the cavity
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Sliding table o To maintain alignment
o To support the weight
adjustable pods o Vertical displacement of the cavity
to anticipate for the alignment
MAX School
P. 46
GRP WITH SUPPORT POSTS
Support posts
DIFFERENT CONCEPTS OF SUPPORTING
 Use Helium GRP as structural support
• Large diameter pipe (because of pressure drop)
 Use composite thermalized support posts
• At the centre: support fixed to the vessel
• At the extremities: sliding supports for removing the effect of thermal
contractions of the GRP
Gas
Return
Pipe
Vacuum
vessel
Cold
mass
 Use sliding supports and invar rod
• The thermal contractions of the GRP are not transmitted to the cavity
• Longitudinal position of the cavity is fixed by invar rod
Example: TTF Tesla Test Facility cryomodule
Same solution for XFEL and ILC
Support post
Vacuum vessel
GRP
Invar rod
2 phase
pipe
Sliding
support
Coupler
port
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70K shield
4K shield
Cavity
P. 47
DIFFERENT CONCEPTS OF SUPPORTING
SPACE FRAME
 Using of a space frame
• The alignment of the string of cavities is realized outside the
vacuum vessel
• The alignment is then realized by adjusting the vacuum vessel with
an external referential (transfer beam axis)
 Using of the antagonist rods
Preserve the alignment of the cavities
Vacuum vessel
Tie rods
Spaceframe
Cold mass
Pad supports
Example: ESS Cryomodule for elliptical cavities (solution type SNS)
Biphasic He pipe
Spaceframe (300K)
50K Thermal
shield
Supporting rods
He tank &
Cavity
Positioning
jacks
(3 at 120°)
Coupler
Vacuum vessel
Door knob and
RF wave guide
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P. 48
OTHER: SUPPORTING BY POWER COUPLER
DIFFERENT CONCEPTS OF SUPPORTING
 Using of the double walled tube of the power coupler as support
• Provides the alignment of each cavity along beam axis (fixed point)
 Using of the inter-cavity supports
• Relative sliding between adjacent cavities along the beam axis
• Provides a second vertical support (limits vertical self-weight sag)
Example: SPL SHORT CRYOMODULE
Inter-cavity supports
RF coupler double-walled tube
flange fixed to vacuum vessel
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P. 49
CONTENTS
 INTRODUCTION
 BASIC FUNCTIONS
 MAIN COMPONENTS
 THERMAL ASPECTS
 MECHANICAL ASPECTS
 DIFFERENT CONCEPTS OF SUPPORTING
 ASSEMBLY PROCESS
 CRYOGENIC SCHEME OF A CRYOMODULE
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P. 50
ASSEMBLY STEPS
ASSEMBLY PROCESS
 Inside the clean room
• Assembly of the string of cavities with its power couplers with a preliminary
alignment
 Outside the clean room: Insertion of all components inside the vacuum vessel
• Assembly of the other equipments of the string of cavities: Cold tuning system,
magnetic shield, instrumentation,...
• Assembly of the thermal shields, cryogenic distribution lines,...
• Insertion inside the vacuum vessel
• Procedure of alignment
For each step, it’s necessary to provide:
- Some specific tooling
- Some suitable infrastructures
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P. 51
ASSEMBLY PROCESS OF CRYOMODULE B – SPIRAL2
Inside the clean room:
Assembly of the cavity with:
- the power coupler
- the cold tuning system (CTS)
CTS
Insertion and connections of the
cavities in the intermediate part
of the vacuum vessel:
ASSEMBLY PROCESS
Cavities
Clean room
handling
apparatus
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Power coupler
One part of the
vacuum vessel
MAX School
Transport
carriage
P. 52
ASSEMBLY PROCESS OF CRYOMODULE B – SPIRAL2
Outside the clean room:
ASSEMBLY PROCESS
Magnetic shield & MLI
Closing of the top cover
Raising of the assembly
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Top plate with cryogenic
line, part of thermal shield
Withdrawal of the carriage
MAX School
thermal shield
Finish with the bottom
of the vacuum vessel
Cylinder of the vacuum vessel
Ready to be tested
P. 53
ASSEMBLY PROCESS OF MAX CRYOMODULE
Outside the clean room:
Inside the clean room:
Assembly of the string of cavities with
the power couplers on the sliding table
Pre-alignment
Finalization of the dressing of the cavities:
- Cold tuning system,
- Magnetic shield,
- Some cryogenic pipes,
- thermal shield
ASSEMBLY PROCESS
Adjustment of
alignment
Cryostating:
- Displacement of the vacuum vessel for the insertion
- Assembly of supporting posts,...
- Closing of the vacuum vessel
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P. 54
ASSEMBLY PROCESS OF ESS SPOKE CRYOMODULE
Outside the clean room:
Inside the clean room:
Assembly of the string of cavities with
the power couplers on a specific tooling
Finalization of the dressing of the cavities:
- Magnetic shield,
- Some cryogenic pipes,
- Supporting rods
- Thermal shield
ASSEMBLY PROCESS
Pre-alignment
Cryostating:
- Insertion in the vacuum vessel
- Assembly of supporting rods
- Cold tuning system, cryo. Pipes,...
- Closing of the vacuum vessel
Adjustment of
alignment
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P. 55
ALIGNMENT
Objective:
Align the beam tubes of all cavities along the beam axis.
The beam tubes are not accessible when the cryomodule is close
Transfer the beam tubes axis: External references (new fiducials)
ASSEMBLY PROCESS
1. Align the cavities inside the cryomodule
2. Align the cryomodule with respect to the others
Measurement equipments:
retroreflector
Laser tracker
Total station (Theodolite)
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Taylor Hobson sphere
P. 56
ALIGNMENT STRATEGY FOR CRYOMODULE B SPIRAL2
Offsets of the beam axis on the helium vessel:
The tolerated maximum static errors for the global alignment are:
- ± 1 mm for the displacement of the cryomodules
- ± 0.3° for the rotation (X,Y) of the cryomodules
2nd offset axis
1st offset axis
ASSEMBLY PROCESS
Beam axis
2nd offset axis
1st offset axis
Fiducialization bench (=section of the linac structure):
- Alignment of the cavities in the cryomodule
- Offset the beam axis on the support of the cryomodule
Beam axis
2 Offset axes
of the cavity
Offset axis of
the cryomodule
Reference axis for alignment of all
components on the accelerator
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P. 57
ALIGNMENT OF SPL CRYOMODULE
Example of budget tolerance: SPL Cryomodule
ASSEMBLY PROCESS
Specific tooling for the alignment
of the string of cavities:
4 spheres by cavity to
adjust the alignment
Step
Cavity and He vessel assembly
± 0.1 mm
Supporting system assembly
± 0.2 mm
Vacuum vessel construction
± 0.2 mm
Transport and handling
(± 0.5 g any direction)
N.A.
± 0.1 mm
Testing/operation
Vacuum pumping
Cool-down
RF tests
Warm-up
Thermal cycles
± 0.2 mm
Cryo-module assembly
2013/10/02
BUDGET OF TOLERANCE
Sub-step
Tolerances (3σ)
MAX School
Total envelopes
Positioning of the
cavity w.r.t. external
referential
± 0.5 mm
Reproductibility/
Stability of the cavity
position w.r.t. external
referential
± 0.3 mm
P. 58
CONCLUSION
The mechanical design of a cryomodule depends on a variety of parameters
that need some knowledge in:
CONCLUSION
Mechanical, thermal, vacuum and cryogenics.
At IPNO Laboratory, the mechanical design of the cryomolules is assumed by the
design office:
- 6 engineers
- 7 draughtman designers
Supported by other colleagues from the Accelerator Division (total: 90 persons):
- Expert in cryogenics and vacuum
- Expert in RF cavity design
- Expert in beam dynamics
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P. 59
References
• H. Saugnac, IPN Orsay, “Cryostat : construction et mise en oeuvre”, Journées cryogéniques d’Aussois, 2003
• Paolo Pierini, INFN-Milan, “overview of cryomodules for proton accelerators”, ESS Bilbao initiative workshop, 2009
• N. Ohuchi, KEK, “Fundamentals of cryomodule”, SRF 2009 tutorial program, 2009
• T. H. Nicol, Fermilab, “Fundamentals of Cryomodule Design: Theory and Practice, Part II – Mechanical Considerations”, SRF
2011 tutorials
• V. Parma, CERN, “Cryostat design II: Application to cryostat design”, Cryostat Design Seminar at GSI, 2005
• H. Saugnac, IPN Orsay, “Design review of the SPIRAL2 cryomodule B”, 2008
• P. Duthil, S. Rousselot & P. Duchesne, IPN Orsay, “ SPL Cryomodule Conceptual Design Review - Vacuum Vessel and Assembly
Tooling”, 2011
• D. Reynet, P. Duthil & S. Bousson, IPN Orsay, “Engineering Design of the ESS Spoke Cryomodule”, SLHIPP meeting, 2013
• G. Olivier & J.P. Thermeau, IPN Orsay, “ESS Cryomodule for elliptical cavities (Medium and high beta)”, SLHIPP meeting,
2013
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P. 60
THANK YOU FOR YOUR ATTENTION
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P. 61