WORKSHOP ON ACCELERATOR OPERATION

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

JAPAN

By Philippe Duru – Operation Group - ESRF

Minimizing Minimizing radiation radiation and beam losses at and beam losses at

thethe ESRFESRF

8Operators24h/24hRun time47Beamlines

5600Hours/year

200 mAIntensity6 GeVEnergy

ElectronsParticles

EUROPEAN SYNCHROTRON RADIATION FACILITY – Grenoble (France)

1. To Operate the Machine in the cleanest way,

Objectives:

2. To fulfil the Radiation protection Regulations and ensure Personnel Safety,

One outcome of these efforts:

INJECTION WITH FRONT END OPEN IN ROUTINE OPERATION

European DirectivesRadiation limit in the Experimental Hall

ESRF Experimental Hall is classed as a « Free access « zone:

Annual dose limitation = 1mSv

Yearly working time = 2000 hours

Dose rate limitation = 0.5 µSv/h (2,5 µSv/h before year 2000)

ESRF Personnel classed as « non exposed »

To operate the Machine in the cleanest way:

Types of Types of losseslosses

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 studiesLosses mechanism studies

Create electron losses at nominal energy and analyse radiation 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 Choice of of detectordetector

Photon (keV to 100 MeV) and Neutron (eV to 100 MeV) detection:

•During Injection: pulsed radiation•During total beam loss: intense radiation

•With stored beam: 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 electrometerReliability, High dynamic range + High price

5 litres Argon at 10 bars located under first dipole of each cell UNIDOS electrometer

• Installed inside the storage ring on the floor, below the first dipole magnet of each cell, they measure absolute values and have a large dynamic range (nSv to Sv).

• Shielded from Synchrotron radiation with 10mm of lead in order to measure only Bremsstrahlung radiation.

Price: 10200 EurosMaintenance cost: calibration cost

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 the horizontal plane of the beam path, they are sensitive enough to measure moderate beam losses in stable stored beam andhave a fast response time.

• They are mostly used during Machine studies.

Price: 1800 Euros

Photo-Multiplier from Electron Tubes or Hamamatsu

Shielding shutter

Perspex fibre d=25 mm

1-cm lead global shielding

γ

Front End

BLD

e e

e

γ

BLD 1 informs about losses in the straight section

BLD 2 about losses in the achromat

Control and Monitoring of the Detectors

2 beam loss detectors per cell

Number of cell

Dose rate

Dose rate

1 ionisation chamber per cell

Number of cell

Bremsstrahlung Detector(Under development)

•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 located at both ends of the straight section vacuum vessel, it is then impossible to determine the vacuum pressure over the full length accurately.

One prototype installed in the Storage Ring

γ

γ e-e+

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 the injection 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 the crew on shift,

Diagnostics Tools - 23. Scrapers:

• Optimum closure of scraper jaws is a compromise between lossesand 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 theStorage Ring;

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

• The product I(mA)xP(mBar) is monitored for each cell. If a given 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 important matter contributes to the improvement of the protection of

personnel and equipment.

One example of correlative analysis

PressurePressure

Lifetime

Beam current

Beamloss

Machine studies

2. Reinforce and improve Radiation shielding, also motivated by future higher current in the Machine whilst respecting legal annual dose,

4. Monitoring of Radiation level in the Experimental Hall,

5. Minimize Bremsstrahlung losses,

6. Implementation of Safety procedures,

Several tracks to achieve the best protection of Personnel and Environment

7. Construction of a shielded hutch to store activated pieces of equipment,

1. Recall of European Directives fixing new annual dose in free access zones,

3. Fence off the zones where radiation may reach the limit duringroutine operation and Machine days,

European DirectivesRadiation limit in the Experimental Hall

ESRF Experimental Hall is classed as a « Free access « zone:

Annual dose limitation = 1mSv

Yearly working time = 2000 hours

Dose rate limitation = 0.5 µSv/h (2,5 µSv/h before year 2000)

ESRF Personnel is classed as « non exposed »

Additional lead shielding on tunnel’s concrete structure,

… on false floor’s tiles covering cables and piping trenches,

… around RF waveguides on top of Storage Ring roof,

Reinforce and improve Radiation shielding

Steel/Lead covers Shielded rotating sill

Shielded false floor’s tilesShielded chicanes

64 Neutron detectors have been installed on the roof of the Storage Ring to monitor the ambiant radiation level of the Experimental Hall and to assure the dose rate limitations.

Monitoring of Radiation level in the Experimental Hall

ApfelApfelREMbrandtREMbrandtTMTM

SDDSDD--100 vials100 vials

SensitivitySensitivity: 7 : 7 bubbles per bubbles per µµSvSv

Not Not used used as as onlineonline diagnostic but as diagnostic but as integrating integrating diagnostic, to diagnostic, to survey the overall lossessurvey the overall losses, , loss loss distribution distribution and and radiation radiation

protection.protection.

Price: 5500 EurosMaintenance: 150 Euros/year

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

Monitoring of Radiation level in the Experimental Hall

2 Neutron detectors per cell

2µSv: Injector Interlocked

1µSv: Alarm in Control Room

Cell 4 neutron detectors

located in a fenced area

(injection zone)

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 of vacuum chambers and prior to delivering the beam to the Users,

To minimize Bremsstrahlung losses

Improve Vacuum chamber design, material and coating

“10 mm” Al (57x8) HOR x VER Elliptical Aperture, 5073 mm Long

Improve Vacuum chamber design, material and coating

he choice of a design, a material and a coating is a compromise

between cost and quality,

or low gap chambers, NEG coated aluminium profile allows quite a

short conditioning time and therefore reduce sthe downtime

after vacuum intervention for beamline operation.

10mm SS uncoated15mm Al coated

10mm SS coated

Vacuum conditionning

Dynamic pressure DP/I (mbar/mA

Integrated beam dose (A*hour)

Upstream pressure (thermal effect due to absorber)

Downstream pressure (without absorber)

1. Implementation of Safety procedures for R & D activities usingthe 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 of

diagnostic 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 anyMachine-related equipment,

Reinforcement of Safety policy

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

Management of parts removed from tunnels

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.

Construction of a shielded hutch to store activated pieces of equipment

Work permit for any

intervention on Machine

equipment

European Synchrotron Radiation Facility

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: Period of validity (to be filled by Operation) I certify that all the conditions and hazards

have been explained to the persons under my responsibility and in charge of the works.

The ESRF person in charge of the intervention: 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 and access 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):

White: Responsible of intervention – Yellow: Operation group

Name, signature and date

PERMIT TO INTERVENE DURING MDT

M.D.T. of: (Day/month/year/time)

Signature and date

RP name, signature and date

My signature is needed after intervention: YES NO

TO BE RETURNED TO THE CTRM AFTER COMPLETION OF WORK

Name, signature and date

RP name, signature and date

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,

To ease interventions during breakdown or maintenance shutdown

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 installation and control has been set up to avoid any similar event.

Injection with Front Ends open

OBJECTIVE:OBJECTIVE:

To reduce the thermal load variation during injection on the beamline optics.

CONSTRAINTS: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: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 the dose 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 the dose limit is reached.

Radiation monitor on every Beamline

Control and Monitoring

75% of normalize dose: Alarm

100% of normalize dose: BL shutter closure

42 beamlines

In conclusionIn conclusionTo comply with the new European Directives theESRF 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 conclusionIn conclusionTo comply with the new European Directives theESRF 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.