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Diamond Project Close-out Report
Project Title
Crystal Clamping Project
Project Manager
Peter Docker
Date
02/12/14
Budget
£13,000
Committed
£10,878
Expenditure
£10,749
Project Start
Apr-13
Planned Project End
Nov-13
Actual Project end
Aug-14
1. Project Summary and Conclusions
Brief overview of the project, and whether objectives were achieved,
Overview of Project
The project was initiated to explore different clamping regimes for the first crystals for the I20
monochromator. As the crystals are cooled by indirect clamping, clamping forces are required to
achieve and maintain a sufficient thermal interface whilst not imposing detrimental mechanical strains
within the crystal. These tests were instigated to try and explore different indium thicknesses and pre
clamping pressures on crystals performance due to cooling and potential mechanical distortion.
Before the tests detailed in the project proposal were started remedial tests were carried out to
explore the crystal/ heat exchanger interface using pressure sensitive paper and a load cell was used
to ensure clamping pressures applied by calibrated springs were in fact applying the pressures
assumed. Once these tests were completed 3 thicknesses of Indium were explored with 3
preclamping pressures. Each configuration was then cooled to cryogenic temperatures in a vacuum
environment and interrogated optically using the miniFIZ interferometer. The results from these tests
were used to try and predict an optimum configuration which was then interrogated using X-rays on
B16. Interrogation was carried out to determine if the data yielded from the miniFIZ does represent
how the clamping regime will perform when exposed to X-rays. This is vital as it will determine
whether miniFIZ results are pursued for future interrogation of monochromator crystal clamping
configurations. On completion of the X-ray tests the crystal assembly was checked for alignment
using a laser to see if the assembly had maintained alignment during the Xray tests.
During this project new hardware was developed as an additional project to facilitate the crystal cage
to be cooled with flowing LN2 as it is in service at the same time as being able to input up to 200
watts of power into the crystal surface. This was modelled with good correlation in the empirical and
modelled results.
Load cell tests
The Belleville washers that hold the crystal clamping assembly together in service and the helical
springs used to apply the preload to the sample used to yield the indium prior to service were
calibrated by clamping a load cell as shown in figure 1 and figure 2.
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Figure 1 Callibration of Belleville washers
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Figure 2 Callibration of helical springs
By deforming the different spring configurations with the load cell incorporated true loads for known
spring compressions could be obtained and predicted loads clarified
Figure 3 Load cell test results
For the helical springs it was found that the load they were applying for a given compression was only
half the load predicted. This resulted in the overal force applied to the copper cooling cheek and
crystal was not sufficient nt to yield the indium placed at their interface. The data from this graph
allowed for loads to be applied to the crystal assembly that would yield the indium when required. The
spring rate for the Belleville washers was incorrect by 20% and the data again allowed for accurate
clamping of the crystal assembly.
Use of pressure sensitive paper to analyse crystal / heat exchanger interface.
This paper is manufactured by Sensor Products Inc and is called Pressure-micro Green. Two
separate films are placed together in the interface and the pre load is applied to give a predicted
pressure and released. The paper records the positions of maximum pressure and indicates if the pre
load is in fact exerting a unifrom pressure or very high localised pressures.
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Initial trials showed that the heat exchangers to be used in these tests did not clamp the crystals with
uniform pressure.
Figure 4 Crystal clamped between heat exchanger of the current design
Figure 5 Same crystal clamped between solid cheeks
From figure 4 it can be seen that the pressure applied to the crystal surface is not uniform. The
reasons why the pressure is such is due to the cooling channels within the heat exchanger
deforming. This problem could be corrected by increasing the thickness of the cheek walls. In this
case if it is believed that the load is being supported by only 20% of the crystal surface then
pressures applied in these areas are 5 times higher than expected. Note the excessive pressure
adjacent to the crystal surface, a part of the crystal required to remain unstressed in service. When
compared to the paper clamped between solid heat exchangers seen in figure 5 where it can be seen
a good uniform pressure has been applied. A pressure that has been presumed between heat
exchangers such as those in figure 4 that are currently in service
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Tests carried out using the MiniFIZ
During these tests, solid heat exchangers were manufatured to eliminate the unknown contribution of
uneven clamping. Pressure has major influence on thermal conductance between interfaces. 9 tests
were carried out using a 3 indium thickness’s and three preclamping pressures and one clamping
pressure applied to maintain the interfaces during service. The experimental set up can be seen in
figure 6
Figure 6 Crystals mounted for MiniFIZ tests
MiniFIZ / X ray measurments
The application of the MiniFiz for measuring strains in clamped crystals was investigated. Changes in
surface deformation were identified. Three indium thickness’s were used (100, 250 and 500 micron)
in colaboration with three Preclamping pressues (0, 1 and 2 MPa) and one holding pressure
(0.02MPa). An example of surface maps can be seen below in Figure 7
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Figure 7 Examples of miniFIZ results
The pressures that yielded the least deformation along with the optimal indium thicknesses thermally
were applied to a final configuration to be tested on B16. For reference these were 500micron indium
preclamped to 2MPa and held at 0.02MPa with the idium cut back 1cm from the top surface. The set
up for these tests can be seen in figure 8 and 9. The vacuum vessel and crystal cage mounting
configeration had to be altered and Kapton windows fitted to allow for the X ray tests
Figure 8 ProE image of setup for X ray tests on B16
Figure 9 Schematic of apparatus used to measure strains in test crystal at B16. The diffractometer
was not used but is included for reference.
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Results form the X ray tests carried out on B16 can be seen S:\Science\Optics\Crystal
clamping\B16_NT4920_ExpRep.docx
As the tests progressed it became clearer that the result for each test was ‘stand alone’ in that none
were directly comparable to other tests configurations. Components in the test cell like the window
orientation added error to the results that differed between tests. Mechanical assembly needed more
consideration. How the crystal cage was to be mounted for measurement would yield discrepancies in
the results. Expecting cooling by conduction to a fixed cryostat of LN2 rather than a continuous flow
through the side cheeks would also add doubt to performance in service. The current clamping
configuration does not lend itself to being assembled in a repeatable manner. Macro tools are used to
assemble a configuration that requires sub micron accuracy. Even the smallest of differences in
mounting forces will affect the crystals orientation and structure. Indium preperation and surface finish
all have to be considered with direct cooling. Since the use of the pressure paper has become
available, similar uneven clamping has been identified with big mirror assemblies (see figure 10) but
due to the low powers they are exposed to, this unknown issue has not become a problem. This is
also the case with the cooling of monochromator crystals with side cooled crystals with lower power
requirements that such configurations are suitable.
Figure 10 Results from using pressure paper on a large mirror assembly
The key result drawn from the tests carried out on B16 is that the results from the MiniFIZ are not
directly comparable with the real performance that a crystal set up will give when used with X rays.
Only after doing both can you determine whether the data would be accurate. See report
S:\Science\Optics\Crystal clamping\B16_NT4920_ExpRep.docx. It was found after the system was
brought back up to room temperature that the crystal were optically not still aligned. This highlights
the issues with clamping crystals in such a configuration. There is no component ensuring alignment
is maintained. Clamping forces are required to ensure alignment, thermal throughput and to not
distort the crystal lattice. Errors incurred by such a configuration can continue to perform in more
foregiving power/ crystal regimes. In addition alignment was only achieved by non uniform clamping
of the indium at the crystal heater exchanger interface. During the project it was found this kind of
configuration required a lot more personal ‘knowhow’ than technical rigor in assembly.
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Test rig for temperature measurements for Monochromator first crystal assemblies under
cryogenic cooling.
Introduction
A test rig was built to allow for power to be input into a monochromator crystal’s surface as it would in
service due to X ray power. The system uses a 200 watt 15mm square heater which can have the
power varied to it in increments. This system facilitated flowing LN2 cooling as the crystal would see
in service by being able to connect directly to a cryocooler. These tests were not previously possible
at Diamond
Set up
Below can be seen the complete set up with key parts labelled. The cryocooler and the vacuum cart
do not need explanation but the other key parts are detailed in the subsequent sections
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Figure 11 the complete set up
Crystal cage set up
Figure 12 details the crystal cage assembly with the power input system and PT100 thermometry
attached. The heater is clamped in place with a Peek beam with a PT100 positioned on top of it. Data
will then be compared to FEA models to validate them. This would allow the worker to generate
empirical data on proposed cryo cooling regimes being used on current monochromators and review
performances for future designs. Peek was used to clamp the heater and to isolate the crystal cage
from the chamber to ensure power generated by the heater was absorbed into the cooling system
ignoring the negligible loss due to radiation
Figure 12 Crystal cage
Power Supply
The power supply is limited to 52 volts for Health and Safety but can supply up to 1500 watts at 30
amps. The heater element was 15mm squared and rated up to 200 watts. This power was
incrementally increased and the PT100 readings taken at each power increase once the temperature
increase had reached steady state.
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Figure 13 Power supply, feed through and heater element
The Chamber
The figure below details the ports on the modified vacuum chamber. By facilitating flowing LN2
through the heat exchangers of a crystal cage ‘true, in service’ conditions can be interrogated off line.
The chamber was designed to include a burst valve set to burst catastrophically at 0.2bar above
atmospheric to protect the user in the event of a LN2 leak in the vacuum chamber.
Figure 14 Modified vacuum chambers
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Initial results and FEA comparison
The experiment was modelled using COSMOS FEA that runs from Solid works software. The
components were all modelled as having intimate contact and the thermal conductivity entered as
such as it changed with temperature. Below are some snapshots of the FEA showing the heater
emitting 200watts and its direct affect on the crystal below it. Note the PT100 on the copper cheek
only increased in temperature by 1kelvin so was modelled as a constant
Figure 15 Model set up
Figure 16 FEA of configuration receiving 200 watts of power
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Figure 17 Subsequent heat being input into the crystal surface
The results below show very good correlation between the FEA and experimental.
temp increase versus FEA prediction
110
Temp Kelvin
105
100
95
90
FEA
Experimental
85
80
0
25
50
75
100
125
Power Watts
150
175
200
Figure 18 Comparison of experimental PT100 readings compared to FEA model (note measurements
taken from top surface of the heater in Figure 16)
This correlation gives confidence in assumptions made in the model allowing more predictive
exploration in future designs. The model was kept the same and the heater removed and power input
directly into a known area on the surface to mimic beam hitting the crystal’s surface.
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Figure 19 Configuration of model inputting power directly into the crystal
Figure 20 Temperature gradient with 1000watts entering the crystal’s surface
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Figure 21 Section of crystal temperature gradients within the crystal
power in v temp increase
115
110
Temp Kelvin
105
100
95
90
85
80
0
100
200
300
400
500
600
700
800
900
1000
Power (watts)
Figure 22 Temperature increase with Power
From this model we can see there is a predicted increase in local temperature of the crystal surface of
approx 30 Kelvin at 1000watts. The assumptions made in this modelling will be directly fed into to the
work that will be carried out by the PhD studentship this project has yielded with Birmingham City
University. If further tests prove to correlate with their models many virtual iterations of cooling
regimes can be explored prior to any hardware being manufactured. The test rig developed in this
work will prove invaluable in future cryocooling designs.
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Conclusions
 Load cells allow true calibration of clamping fixtures such as Bellevile washers and springs

The pressure sensitive paper allows future clamping configurations to be investigated for
uniformity in mating surfaces

The Minifiz system can measure optical surfaces for flatness to micron accuracy. Due to
mechanical assembly a system can only be confidently measured in its final assembly. If
further reasembly is required future performance cannot be guarenteed by earlier results

More understanding of the ‘errors’ incurred by the measuring stages needs to be understood
such as the windows. To allow the user to know if the error by the windows is big enough to
mask the potential difference presented by a different configuration being tested

Results measured using the MiniFIZ do not directly aid prediction of how a configuration will
perform under Xray conditions.

Unless cooling and mounting of a configuration can be presented to the beam during the X
ray tests on B16 results wont reflect performance in service.

Exhaustive FE analysis is required to fully understand what forces can be applied to a crystal
to deform it sufficiently that it is unable to perform its purpose. This in turn should be compared
with clamping forces required to ensure good thermal throughput for the unwanted Xray
power to the cooling system.

The PhD with Professor Mike Ward at BCU as a collaborator to investigate such current
configurations and explore future approaches is due to start on the 3rd of November

There is a need for a system that can be assembled repeatably and not require ‘black art
know how’ to attempt full alignment

Decoupling of alignment clamping forces and cooling is desirable

Reports obtained during the duration of the project detailed direct cooling approaches that are
already in service and can meet the power requirements we require.

Current crystal clamping configuration needs to be addressed:
o
o
o
Single crystal configuration
New crystal cage design
Move over to direct cooling

The new chamber shows great promise for facilitating the input of power into optics whilst
under service conditions

The New system allows for empirical data to be obtained to input directly into the models
being developed in the PhD program being run with BCU
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
These tests were hard to schedule for, as there is no complete spare Cryocooler. If Diamond
sees the facility to test cryocooled assemblies and input power routinely then the spare
cryocoolers should be fully recomissioned

A need for short and long term plan to be discussed
Lessons learnt
Ensure full assembly protocol is documented and repeatable
Ensure external influence on the assembly is considered. For example in this assembly the
connection to the LN2 system could have significant affect on any pre alignment
Ensure mechanical interfaces are as predicted using pressure paper and load cells
Current clamped direct cooling assemblies are not repeatable.
Non uniform clamping to achieve alignment may well not remain permanent in service due to
relaxation/movement within the indium interface
Recommendations
Consider direct cooling for I20 and for future beam lines with high energy requirements for the
following reasons:




Allows for decoupling of clamping forces on cooling performance
No interface material required to ensure cooling performance
No clamping forces required that will actively deform the crystal
A currently available system is in service capable of meeting the power demands we need
Run the PhD with BCU to review current and ‘blue sky’ future designs (completed)
Re-commission the spare cryocoolers