Hugo Shiers - VACUUM SYMPOSIUM

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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.

Hugo Shiers - VACUUM SYMPOSIUM

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