Advanced Endplate - mechanics:
Development of a Low-Material TPC Endplate for ILD
Dan Peterson
Laboratory for Elementary-Particle Physics, Cornell University
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The ILD central tracker is a
TPC
with
outer radius 1808 mm
inner radius 329 mm
half length 2350 mm
Reporting on R&D
toward the mechanical endplate of the ILD TPC
which, along the way,
involves a new endplate for the LCTPC LP1
and other small prototypes.
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Goals of the ILD TPC endplate
Detector module design:
Endplate must be designed to
implement Micro Pattern Gas Detector (MPGD) readout modules.
Modules must provide near-full coverage of the endplate.
Modules must be replaceable without removing the endplate.
Low material - limit is set by ILD endcap calorimetry and PFA:
25% X0 including readout plane, front-end-electronics, gate 5%
cooling
2%
power cables
10%
mechanical structure
8%
Rigid - limit is set to facilitate the de-coupled alignment of
magnetic field and
module positions.
Precision and stability of x,y positions < 50μm
Thin - ILD will give us 100mm of longitudinal space
between the gas volume and the endcap calorimeter.
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In 2008, Cornell constructed two endplates for the LCTPC Large Prototype (LP1).
These were shipped August 2008 and February 2010, and are currently in use.
Inside the chamber
Outside the chamber
The endplate construction was developed to provide the precision required for ILD,
precision features are accurate to ~30 μm,
but not to meet the material limit specified for the ILD TPC;
the bare endplate has mass 18.87 kg over an area of 4657 cm2,
(mass/area) / (aluminum radiation length (24.0 g/cm2) ) = 16.9% X0,
2x the goal.
The accuracy was achieved with a 5-step machining process developed at Cornell.
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The ILD endplate design is a space-frame
and shown here as the solid model used for
the Finite-Element-Analysis (FEA).
(inside view)
This is the “equivalent-plate” design space-frame; the separating members are thin plates.
This design has rigidity and material equivalent to a strut design, which has also been studied.
(More on that later.)
This model has a full thickness of 100mm, radius 1.8m, and a mass of 136 kg.
The material thickness is then 1.34g/cm2, 6% X0.
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FEA calculations of deflection and stress (stress is not shown)
Endplate Support:
outer and inner field cages
deflection=0.00991 mm/100N
100N is the force on LP1 due to 2.1 millibar overpressure
(area of ILD)/(area of LP1) =21.9
deflection for 2.1 millibar overpressure
on the ILD TPC endplate (2200N)
= 0.22 mm
Without the space-frame structure,
the simple endplate deflects by 50mm.
rigidity vs thickness
It was expected that the strength could be
improved by asking ILD for more longitudinal space.
However, the improvement with thickness
diminishes (deviates from power law) above 100mm.
Note small buckling in inner layer.
Rigidity is improved with modest increase
in the back-plate thickness.
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This ILD endplate design results from several studies:
LP1 current endplate, measurements and FEA
LP1 space-frame designs, FEA of models,
small test beams,
FEA and measurements.
Future studies will include
construction and measurements
using a new LP1 endplate.
“strut” space-frame design
LP1 2008 endplate
“equivalent plate” space-frame design
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small test beams
that represent
one diameter of the
LP1 endplate
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In the first validation of the FEA,
deflection of the current LP1 endplate was measured and
compared to the FEA.
The load of 100N (22lbs) was placed
“uniformly” in the center module location.
Deflection, measured across 2 lines, agrees on average.
location number
7
6
5
4
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2
1
0
-1
“deflection 1”
-2
-3
-4
Stress is <1% yield.
-5
-6
-7
“deflection 2”
8
Various LP1 models were compared.
mass
kg
LP1
18.87
16.9
33
1.5
8.93
8.0
68
3.2
Al 7.35
C 1.29
7.2
(68-168)
(3.2-4.8)
Al 7.35
6.5
168
4.8
8.38
7.5
23
Lightened
Al-C hybrid
(channeled plus fiber)
Channeled
material deflection stress
%X0
microns
Mpa
(yield: 241)
Space-Frame
4.2
(strut or equivalent plate)
Material: space-frame has slightly more material than
the simple “lightened” design
or the “Al/C hybrid”.
Rigidity: space frame deflects less than LP1,
~3x more rigid than the lightened (all Aluminum),
and (3 to 7)x more rigid than the Al-C hybrid.
The FEA will be will be tested with a constructed space-frame.
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Validation of the FEA with small test beams
2008
The small test beams represent sections of the LP1 endplate
across the diameter of the LP1 endplate (slide 7).
For each small test beam, there is a
solid model that was used for the FEA
and an assembly model for construction.
Al-C Hybrid
Deflection of the small beams was compared to the FEA.
100 mm
The “equivalent plate” space-frame was constructed in carbon-fiber.
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Comparison of deflection for small test beams: FEA vs. measurements
20100408
mass
LP1
0.63 kg
20101111
center load
FEA
mm/100N
0.755
20101104
20110202
20110316
center load
center load
center loaded
MEASURED MEASURED MEASURED
mm/100N
mm/100N
mm/100N
0.88
Al-C hybrid ( 1.0 part fiber : 1 epoxy )
Al-C hybrid ( 0.25 part fiber : 1 epoxy )
LP1 (channeled)
0.37 kg
0.75
0.78
1.71
2.12
2.224
2.40
(channeled for the hybrid, but without adding carbon fiber)
space-frame (“strut”)
space-frame (“equivalent-plate”)
0.76 kg
0.111
0.111
0.11
0.12
0.14
The standard LP1 beam agrees with the FEA, except for some problems
in the first measurement, probably sloppy centering the load.
The “strut” space-frame agrees with the FEA. The model accurately predicts the
strength at the joints and the design is useful for ILD.
The “equivalent-plate” space-frame was made with commercial carbon-fiber
plates that were claimed to have the modulus of aluminum; the modulus is ~20% low.
The cast-in-place carbon-fiber does not come close to having the modulus of aluminum.
(Possibly, with a a heat-cured epoxy, the result would have been better.)
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Deflection of the “strut” space-frame
agrees with the FEA in detail.
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It is possible to simply reduce the material in the LP1 endplate
from 18.85kg to 7.35kg or 16.9% X0 to 6.5 X0,
with a deflection increase to from 33 μm to 168 μm.
But, when the lightened endplate design (or even the LP1 original 2008 design)
is scaled up to the ILD endplate the deflection is unacceptable.
Only a space-frame design provides the rigidity and material limit for the ILD.
The space-frame design, with 100mm total thickness
can be made with 7.5 X0 material and 23 μm deflection.
When scaled up to the ILD endplate, the deflection is 220 μm .
Prototypes of sections have been constructed and compared to the predictions of the FEA.
A new LP1 endplate (another prototype section of the ILD endplate) will be constructed
to further validate the FEA of the ILD endplate,
and understand complexities of the design.
Note that I am typically measure and compare longitudinal rigidity(deflection),
when we are ultimately concerned about lateral rigidity and stability.
Longitudinal rigidity is readily measured in the prototypes;
for now, it gives an indication of the relative lateral rigidity and stability.
Stability will be monitored in longer term studies of a new LP1 endplate.
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The next phase of prototyping/validation in the ILD endplate study:
construction and measurement of a fully functional LP1 endplate in a space-frame design.
The “strut” space-frame is chosen because the construction is simpler.
The “equivalent plate” design was developed because the FEA failed for ILD in the “strut” design.
The “equivalent plate” while providing a simple model for the FEA, is more difficult and messy to construct.
How does one glue in the plates beyond #3 ?
The solid model has been converted to an assembly model,
compatible with LP1 modules, field cage, field cage termination, alignment devices.
There has been further lightening of the mullions.
Modification of the outer scallops (from that of the original solid model) allows 2-axis, vertical tool machining.
Mass: 6.56 kg in main plate, 0.81kg in back plate, 1.72kg in struts, =9.2 kg total
(LP1 2008 = 18.9 kg)
(Some mass is added due to the reality of the mounting fixtures and machining tools.)
The bid is in; I will make 2.
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New “module backframes”
will have ~50% of the original mass,
slightly more clearance.
New “mounting brackets”
are required to clear the strut mounts.
Different versions are required for
new and old module backframes.
The entire assembly will be
available for testing in 2012.
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Summary
There has been modeling and FEA at several scales of ILD development:
small beams, LP1, ILD.
The space-frame design is expected to provide the required rigidity
and is a viable construction.
A “strut” space-frame version of the LP1 endplate will be constructed
this summer for further study of this possible ILD design.
lateral rigidity and stability: much more work is required
The new space-frame version of the LP1 endplate will be used in this study.
The preliminary ILD spaceframe design can provide
0.22 mm deflection (2.1 millibar overpressure)
with a contribution of 6% X0 material (bare endplate)
and 2% X0 from the module back-frames.
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Summary Slides
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Goals of the ILD TPC endplate
Detector module design:
Endplate must be designed to
implement Micro Pattern Gas Detector (MPGD) readout modules.
Modules must provide near-full coverage of the endplate.
Modules must be replaceable without removing the endplate.
Low material - limit is set by ILD endcap calorimetry and PFA:
25% X0 including readout plane, front-end-electronics, gate 5%
cooling
2%
power cables
10%
mechanical structure
8%
Rigid - limit is set to facilitate the de-coupled alignment of
magnetic field and
module positions.
Precision and stability of x,y positions < 50μm
Thin - ILD will give us 100mm of longitudinal space
between the gas volume and the endcap calorimeter.
20110518-LCTPC-Peterson
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The ILD endplate design is a space-frame
and shown here as the solid model used for
the Finite-Element-Analysis (FEA).
This model has a full thickness of 100mm, radius 1.8m, and a mass of 136kg.
The material thickness is then 1.34g/cm2, 6% X0.
This is the “equivalent-plate” design space-frame; the separating members are thin plates.
This design has rigidity and material equivalent to a strut design, which will be used for a new LP1 endplate.
20110518-LCTPC-Peterson
(inside view)
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The next phase of prototyping/validation in the ILD endplate study:
construction and measurement of a fully functional LP1 endplate in a space-frame design.
FEA shows that an LP1 endplate in the space-frame design
with material 7.5% X0, deflects by 33 μm.
when center loaded with the force due to 2.1millibar overpressure.
Also, FEA shows that the current LP1 endplate (2008)
with material 16.9% X0, deflects by 23 μm.
This is confirmed with measurements of the LP1 endplate.
Measurements of small test beams also validate the
FEA predictions of the space-frame properties.
The new LP1 space-frame endplate will be used to
further validate the FEA, understand complexities of the construction, and study lateral rigidity and stability.
It is compatible with LP1 field cage, modules, field cage termination, alignment devices.
Mass: 6.56 kg in main plate, 0.81kg in back plate, 1.72kg in struts, =9.2 kg total
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(LP1 2008 = 18.9 kg)
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