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RGA11 Page 1 of 34
Hugo Shiers Diamond Light Source, UK
RGAs operating on the Diamond Light Source
RGA’s on Diamond
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Diamond Light Source is the UK’s national synchrotron light
source currently with 22 operating beam lines and their
associated experimental end stations. Diamond is
incorporated within a large scale vacuum system and currently
has a total of 196 RGA units installed.
RGAs used on the system are an essential tool to diagnose
vacuum issues such as pressure spikes, contamination and
leaks. The RGAs are used in a qualitative mode rather than
quantitative so an absolute calibration is not required instead
they are normalized using the sum of the peaks against a
standard total pressure gauge.
How these RGAs are calibrated and incorporated into the
Diamond vacuum controls along with examples of problem
solving and monitoring of the vacuum systems using RGAs will
be discussed here.
.
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Purpose of RGAs on Diamond
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• Demonstrate cleanliness of vacuum from conditioning process.
• Leak detection.
• Observing relative gas compositions of the vacuum systems.
• Analysis of pressure bursts in the vacuum system.
• Interlocking.
• Trending gasses with time
• Trending together with beam parameters
Control of RGAs and Data storage on Diamond
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• Need global control of RGAs
• Normalization/calibration of RGAs
• Data storage in Diamond
• Trend data to be incorporated with general Diamond data
• Direct user interface for calibration, leak detection, contamination issues
Storage ring tunnel
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RGA Storage ring
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RGA Installation in Storage ring
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RGA Network
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Primary network
Serial link
Serial
Secondary network connect using remote desktop
Control computers Control
Room user
RGA Electronics
Office Computer
Vacuum Engineer
RGA Head
RGA Head
RGA Head
RGA Electronics
RGA Electronics
IOC
RGA PC
RGA PC, showing communication with EPICS
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RGA PC
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RGA Windows PC Display
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Storage ring cell GUI with RGA
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EPICS control
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EPICS EDMS
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New GUI
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Vacuum RGA viewer
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Tuning and calibration procedure
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• Tune high and low mass resolution to get 10% valleys
• Tune mass alignment to get peaks in the correct place
• Calibrate so that sum of masses is equal to total pressure gauge
RGA local control spectra of Arc04 showing easyview tuning window
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Analogue signal showing total pressure as Sum of scanned masses.
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RGA PC, showing Arc4, RGA-01 in local control
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Show calibration
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Calibration menu
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Kapton insulated wire problem
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IR mirror and x-ray absorber in beamline
B22
Kapton insulated wire problem
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Kapton insulated wire contains unexpected FEP binder which
breaks down due to scattered x-rays
CF3+ also seen with electron irradiation
(5keV) in test system
Solution: remove Kapton insulated wire near x-
ray beam absorber
New RGA display including 69 peak
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RGA Archive data Warming of RF cavity
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Conditioning Storage ring Girders
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Pre-bake
Post Bake
Conditioning of a All metal valve
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Pre bake data
Post condition data
Diamond Storage Ring Vacuum Performance
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• 3.5 years into operation, storage ring
• 3000 A.h of accumulated beam dose at 3 GeV
• Static pressure (no beam) 2.6 x 10-10 mbar
• Dynamic pressure (250 mA) 5.6 x 10-10 mbar (spec < 10-9 mbar)
Uncalibrated RGA
scan with beam off
Typically >95% H2,
<5% CO, also CH4,
CO2, H2O + some low
level contaminants at
the 0.05% level
RGA from Pump cart
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Pressure spikes from Ferrofluidic seals
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Oxygen bleed into Mirror vessels
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Conclusions
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•The quality of the vacuum is critical for machine performance.
•RGAs are an essential tool for qualitative analysis of machine vacuum.
•Calibration is limited to normalising the sum of peaks to a local total pressure
gauge.
•Absolute partial pressure calibration is not easily achieved with the quadrupole
and would be difficult to achieve on 100’s of RGAs on the machine. However
normalisation to total pressure is adequate in our case.
•The ability to swap controllers with limited tuning and calibration is proving
important, as it is generally not possible to calibrate the faraday again on the
machine.
•A list of factory defaults for calibration and tuning figures should be available for
each head.
•For a large scale installation the reliability and ease of use is of more importance
than extended functionality.