WORKSHOP ON ACCELERATOROPERATION
2003

March 10-14, 2003, GUAS(Hayama) & KEK (Tsukuba)
JAPAN

Minimizing radiation
and beam losses at
the ESRF
By Philippe Duru – Operation Group - ESRF

EUROPEAN SYNCHROTRON RADIATIONFACILITY – Grenoble (France)

Particles

Electrons

Energy6 GeVIntensity

200 mA

Hours/year 5600
Operators

8

Run time

24h/24hBeamlines

47

Objectives:
1. To Operate the Machine in the cleanest way,
2. To fulfil the Radiation protection Regulations andensure Personnel Safety,

One outcome of these efforts:
INJECTION WITH FRONT END OPEN IN ROUTINEOPERATION

European Directives
Radiation limit in the Experimental Hall
ESRF Experimental Hall is classed as a « Free access « zone:

ESRF Personnel classed as « non exposed »Annual dose limitation = 1mSv
Yearly working time = 2000 hours
Dose rate limitation = 0.5 µSv/h (2,5 µSv/h before year 2000)

To operate the Machine in the cleanest way:
Types of losses
Accurate quantification of radiation induced by varied
types of electron losses:• Injection losses due to transverse and/or longitudinal mismatching of

the injected beam,• Partial or total stored beam loss due to a failure of an equipment(magnet power supply, vacuum valve, etc…), a misalignment of a vacuum
component, etc…
• Bremsstrahlung losses due to collision of electrons with residual gas in
the vacuum chambers,

To operate the Machine in the cleanest way:
Losses mechanism studies

Create electron losses at nominal energy and analyseradiation values:•To correlate internal and external doses with beam current,•To characterize the losses distribution,•To determine precisely the places where unavoidable losses are expected,•To predict the final collision point of electrons on vacuum chamber walls.

To operate the Machine in the cleanest way:
Choice of detector
Photon (keV to 100 MeV) and Neutron (eV to 100 MeV)
detection:•During Injection:•During total beam loss:•With stored beam:pulsed radiation
intense radiation
low radiation

Sensitivity required:
0.5 µSv.h-1 to 100Sv.h-1
And able to measure in dose rate and integrated dose

Radiation monitor: Ionisation Chamber and electrometer
Reliability, High dynamic range + High price••Installed inside the storage ring on the floor, below the
first dipole magnet of each cell, they measure absolutevalues and have a large dynamic range (nSv to Sv).
Shielded from Synchrotron radiation with 10mm of lead inorder to measure only Bremsstrahlung radiation.

5 litres Argon at 10 bars locatedunder first dipole of each cell

Price: 10200 Euros
Maintenance cost: calibration cost

UNIDOS electrometerBeam Loss Detector: Perspex fibre & photo-multiplier
Reliability + Measure moderate beam losses in stable stored beam + Low price••

Located at every dipole magnet exit of each cell, in thehorizontal plane of the beam path, they are sensitive enoughto measure moderate beam losses in stable stored beam andhave a fast response time.
They are mostly used during Machine studies.

BLD
e
e

Perspex fibre
d=25 mm

Photo-Multiplier from Electron
Tubes or Hamamatsu

Front Endeγγ

1-cm lead global shielding

BLD 1 informs about losses in the straight section
Shielding shutter

Price: 1800 Euros

BLD 2 about losses in the achromat

Control and Monitoring of the Detectors

2 beam loss
detectors per cell
Dose
rate
Number of cell

1 ionisation chamber
per cellDose
rate
Number of cellBremsstrahlung Detector(Under development)
One prototype installed in the Storage Ring

γ

e+
e-

γ

•The purpose of this type of detector is to quantify the Bremsstrahlung
radiation passing by the Front End to the beamline.
•It gives also information about the vacuum quality; gauges being locatedat both ends of the straight section vacuum vessel, it is then impossible
to determine the vacuum pressure over the full length accurately.

Diagnostics Tools - 1
1.

A great effort has been made to achieve the best injection
efficiency possible by developing tools associated with BLDs:•

Fluorescent screens and cameras to determine with high precision
the position of beam in the transfer lines,•

Current transformers to calculate, monitor and archive theinjection efficiency,•A « turn by turn » measurement to define time structured losses.

2. Lifetime monitoring and archiving:•

Any unexpected change of lifetime is immediately analysed by thecrew on shift,Diagnostics Tools - 2
3. Scrapers:•

Optimum closure of scraper jaws is a compromise between losses
and lifetime,•

Scrapers limit radiation developing with small gap vacuum
chambers; scraper settings are weekly optimised.

4. Beam Position Interlock:•

Designed to trigger a beam kill by stopping the RF transmitterswhen detecting any deviation of the beam above 700 micrometers.

5. Fuse:•To follow the high frequency coherent beam instabilities; should
the beam reach the instability limit, it would be killed by stopping
the RF transmitters.

Diagnostics Tools - 3
6. Vacuum pressure:•

7 gauges per cell survey the quality of the vacuum in the
Storage Ring;•

Any pressure above 3.10-6 will close the automatic valves andthereby stop the RF transmitters,•

The product I(mA)xP(mBar) is monitored for each cell. If agiven threshold is exceeded the Safety Engineer performs
Bremsstrahlung measurements.

OBJECTIVES REACHED TODAY-

Injection efficiency now close to 100%
Optimisation of settings of in-vacuum undulators (gaps & offsets)
Detection and localization of leak development thanks to correlation
with radiation monitors and beam loss detectors,
Correlation of beam loss location relative to beam loss origin,
Localization and determination of any aperture limitation (physical or
dynamical).

Thanks to these diagnostic tools and their archiving in a huge
database (Oracle), all the events can be analysed:-

Measures are then taken to reduce the amount of losses,
This data leads to an improved understanding of the Machine’s
behaviour.

The unavoidable beam loss locations are well known: This importantmatter contributes to the improvement of the protection of
personnel and equipment.

One example of correlative analysis

Machine studies

Lifetime

Beam current

Pressure
PressureBeamlossSeveral tracks to achieve the bestprotection of Personnel and Environment
1. Recall of European Directives fixing new annual dose in freeaccess zones,
2. Reinforce and improve Radiation shielding, also motivated by
future higher current in the Machine whilst respecting legal
annual dose,
3. Fence off the zones where radiation may reach the limit during
routine operation and Machine days,
4. Monitoring of Radiation level in the Experimental Hall,
5. Minimize Bremsstrahlung losses,
6. Implementation of Safety procedures,
7. Construction of a shielded hutch to store activated pieces ofequipment,

European Directives
Radiation limit in the Experimental Hall
ESRF Experimental Hall is classed as a « Free access « zone:

ESRF Personnel is classed as « non exposed »Annual dose limitation = 1mSv
Yearly working time = 2000 hours
Dose rate limitation = 0.5 µSv/h (2,5 µSv/h before year 2000)

Reinforce and improve Radiation shielding
Additional lead shielding on tunnel’s concrete structure,

Steel/Lead covers… on false
floor’s
tiles
covering
cables andpipingtrenches,

Shielded chicanes… around RF waveguides on
top of Storage Ring roof,

Shielded rotating sill

Shielded false floor’s tiles

Monitoring of Radiation level in theExperimental Hall
64 Neutron detectors have been installed on the roof of theStorage Ring to monitor the ambiant radiation level of theExperimental Hall and to assure the dose rate limitations.
Sensitivity:
Sensitivity: 7 bubbles per µSv

Apfel
REMbrandtTM
SDDSDD-100 vials

Not used as online diagnostic but as integrating diagnostic, tosurvey the overall losses,
losses, loss distribution and radiation
protection.

Price: 5500 Euros
Maintenance: 150 Euros/yearMonitoring of Radiation level in theExperimental Hall

The level is limited to 2µSv (1/3 photons & 2/3 neutrons) over a
period of 4 hours. Should the measure exceed the limit, theInjector is then interlocked.

Cell 4 neutron
detectors
located in afenced area
(injection zone)

2 Neutron
detectors per cell

2µSv: Injector
Interlocked
1µSv: Alarm inControl Room

To minimize Bremsstrahlung losses

1. Improve vacuum chamber design, material and coating,
2. Implementation of protocol to intervene on vacuum component,for dismounting, installation and bake out:•••

Pre-baking of new component,
Nitrogen venting,Monitoring of parameters (Temperature, pressure, time etc…) during
bakeout,

3. Perform Vacuum Conditioning night shifts after any venting ofvacuum chambers and prior to delivering the beam to the Users,

Improve Vacuum chamber design, materialand coating“10 mm” Al (57x8) HOR x VER Elliptical Aperture, 5073 mm Long

Improve Vacuum chamber design, materialand coating

he choice of a design, a material
and a coating is a compromise
between cost and quality,
or low gap chambers, NEG coatedaluminium profile allows quite ashort conditioning time andtherefore reduce sthe downtime
after vacuum intervention forbeamline operation.

15mm Al coated

10mm SS coated

10mm SS uncoatedVacuum conditionning
Dynamic pressure DP/I (mbar/mA

Upstream pressure (thermal effect due to absorber)

Downstream pressure (without absorber)

Integrated beam dose (A*hour)Reinforcement of Safety policy
1.

Implementation of Safety procedures for R & D activities using
the Booster:•••

Avoid losses at high energy during cycle,
Operate Linac gun at 1Hz and not at 10Hz, in long pulse,
Reduced intensity to tune the injection thanks to high resolution ofdiagnostic tools (stripline pick-up, beam loss detectors and current
transformers).

2. New Safety rules regarding the presence of external companies :•No external companies are allowed to work around the accelerators before
Radiation Protection rounds are performed at restart from 5mA to 200mA,•

Restriction of access in tunnels to entitled ESRF staff during interventions
time slots.

3. New work permit to carry out any task at any time on any
Machine-related equipment,

Management of parts removed from tunnels
Every piece, cable or waste coming out of the tunnels is controlled by Radiation
Protection staff.

Construction of a shielded hutch to store
activated pieces of equipment
Located in the accelerator, this hutch has leaded walls and access is limited to
Safety staff. Anything presenting a trace of activation is stored here.

Work permit
for any
intervention on
Machineequipment

European Synchrotron Radiation Facility
PERMIT TO INTERVENE DURING MDTTO BE RETURNED TO THE CTRM AFTER COMPLETION OF WORK
Name of all persons in charge of the intervention:

Place of intervention:
Description of the intervention:

Maximum duration of the intervention:
Removal of RP shields

Dismounting of prot. covers
ladders, false floor tiles, etc...

Please indicate the exhaustive list of items selected above:

Safety (to be filled in by Operation group and Safety group when required)Electrical hazard(s)Equipment to be isolated:
Electrical isolation made by:Radiology hazard(s)Specific individual protection:
Maximal duration of the intervention:

Specific instructions:

RP name, signature and date

My signature is needed after intervention: YES

Period of validity (to be filled by Operation)
M.D.T. of:(Day/month/year/time)

I certify that all the conditions and hazards
have been explained to the persons under myresponsibility and in charge of the works.
Name, signature and date

The ESRF person in charge of the intervention:
Name, signature and date

The Operation Group representative:

Acknowledgement of the completion of work
The works subject to this permit are completed. All equipment has been removed, all protection andaccess means removed by us have been reinstalled and the area is clear of work debris.

The ESRF person in charge of the intervention:
The Safety engineer (if required):NO

Signature and date

RP name, signature and date

White: Responsible of intervention – Yellow: Operation groupTo ease interventions during breakdown ormaintenance shutdown
1. Machine operating low intensity modes are scheduled prior to the
shutdown to limit the risk of equipment activation,
2. Radiation Protection survey of the equipment before any
intervention or, of all the tunnels at the start of the shutdown,
3. Use of non-destructive control, such as radiogammagraphy, on
suspected vacuum components prior to deciding any intervention,

Radiation Protection Map

0,5 µSv/h << 2,5 µSv/h> 2,5 µSv/h

Radiogammagraphy
Example of a damaged RF finger assembly; a procedure for installationand control has been set up to avoid any similar event.

Injection with Front Ends open
OBJECTIVE:
To reduce the thermal load variation during
injection on the beamline optics.
CONSTRAINTS:
To protect the beamline from electron beam,
To protect the beamline from high dose rates due
to injection losses.

Injection with Front Ends open
SOLUTIONS:
Develop a dedicated current monitor, integrated in the
Machine Personnel Safety System, to inject with Front Ends
open IF, AND ONLY IF, 5mA are already stored in the
Machine,Install a Radiation monitor on every beamline to ensure thedose rate limitation:•An alarm is triggered in the Control Room if the dose
rate is above 75% of dose limit,•The Front End shutter is automatically closed if thedose limit is reached.

Radiation monitor on every
Beamline

Control and Monitoring

100% of normalize dose: BL shutter closure
75% of normalize dose: Alarm

42 beamlines

In conclusion

To comply with the new European Directives the
ESRF has been incited to:•Considerably expand the understanding of losses
mechanism and their associated parameters,•Develop precise and reliable diagnostic tools,•Improve the design of the vacuum chambers,•Reinforce the radiation protection shielding,Consequently the operation of the Machine has been
improved.
The crew are now more safety aware during the routine
operation and machine studies.

Acknowledgement
Paul Berkvens, Safety manager, ESRF (F)Patrick Colomp, Safety engineer, ESRF (F)Laurent Hardy, Operation manager, ESRF (F)Roberto Kersevan, Vacuum group manager, ESRF (F)Graham Naylor, Diagnostic engineer, ESRF (F)Ioannis Papaphilippou, Physicist, ESRF (F)Jean Luc Revol, Operation manager, ESRF (F)Kees Scheidt, Diagnostic engineer, ESRF (F)Udo Weinrich, Physicist, GSI Darmstadt (D)In conclusion

To comply with the new European Directives the
ESRF has been incited to:•Considerably expand the understanding of losses
mechanism and their associated parameters,•Develop precise and reliable diagnostic tools,•Improve the design of the vacuum chambers,•Reinforce the radiation protection shielding,Consequently the operation of the Machine has been
improved.
The crew are now more safety aware during the routine
operation and machine studies.