Minimizing radiation and beam losses at the ESRF

Transcription

1 WORKSHOP ON ACCELERATOR OPERATION 2003 March 10-14, 2003, GUAS(Hayama) & KEK (Tsukuba) JAPAN Minimizing radiation and beam losses at the ESRF By Philippe Duru Operation Group - ESRF

2 EUROPEAN SYNCHROTRON RADIATION FACILITY Grenoble (France) Particles Electrons Energy 6 GeV Intensity 200 ma Hours/year 5600 Operators 8 Run time 24h/24h Beamlines 47

3 Objectives: 1. To Operate the Machine in the cleanest way, 2. To fulfil the Radiation protection Regulations and ensure Personnel Safety, One outcome of these efforts: INJECTION WITH FRONT END OPEN IN ROUTINE OPERATION

4 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)

5 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,

6 To operate the Machine in the cleanest way: Losses 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.

7 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

8 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 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. 5 litres Argon at 10 bars located under first dipole of each cell UNIDOS electrometer Price: Euros Maintenance cost: calibration cost

9 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 and have a fast response time. They are mostly used during Machine studies. Perspex fibre d=25 mm 1-cm lead global shielding γ BLD e e Photo-Multiplier from Electron Tubes or Hamamatsu Front End γ e BLD 1 informs about losses in the straight section Shielding shutter BLD 2 about losses in the achromat Price: 1800 Euros

10 Control and Monitoring of the Detectors Dose rate 2 beam loss detectors per cell Number of cell Dose rate 1 ionisation chamber per cell Number of cell

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

12 Diagnostics Tools 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,

13 Diagnostics Tools 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 transmitters when 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.

14 Diagnostics Tools Vacuum pressure: 7 gauges per cell survey the quality of the vacuum in the Storage Ring; Any pressure above 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.

15 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.

16 One example of correlative analysis Machine studies Lifetime Beam current Pressure Pressure Beamloss

17 Several tracks to achieve the best protection of Personnel and Environment 1. Recall of European Directives fixing new annual dose in free access 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 of equipment,

18 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)

19 Reinforce and improve Radiation shielding Additional lead shielding on tunnel s concrete structure, Steel/Lead covers Shielded rotating sill on false floor s tiles covering cables and piping trenches, Shielded chicanes Shielded false floor s tiles around RF waveguides on top of Storage Ring roof,

20 Monitoring of Radiation level in the Experimental Hall 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. Sensitivity: : 7 bubbles per µsv Apfel REMbrandt TM SDD-100 vials Not used as online diagnostic but as integrating diagnostic, to survey the overall losses, loss distribution and radiation protection. Price: 5500 Euros Maintenance: 150 Euros/year

21 Monitoring of Radiation level in the Experimental 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, the Injector is then interlocked. Cell 4 neutron detectors located in a fenced area (injection zone) 2 Neutron detectors per cell 2µSv: Injector Interlocked 1µSv: Alarm in Control Room

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

23 Improve Vacuum chamber design, material and coating 10 mm Al (57x8) HOR x VER Elliptical Aperture, 5073 mm Long

24 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. 15mm Al coated 10mm SS coated 10mm SS uncoated

25 Vacuum conditionning Dynamic pressure DP/I (mbar/ma Upstream pressure (thermal effect due to absorber) Downstream pressure (without absorber) Integrated beam dose (A*hour)

26 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 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 any Machine-related equipment,

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

28 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.

29 White: Responsible of intervention Yellow: Operation group Work permit for any intervention on Machine equipment European Synchrotron Radiation Facility PERMIT TO INTERVENE DURING MDT TO 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) Radiology hazard(s) Specific instructions: Equipment to be isolated: Electrical isolation made by: Specific individual protection: Maximal duration of the intervention: RP name, signature and date My signature is needed after intervention: YES NO 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 my responsibility and in charge of the works. Name, signature and date The ESRF person in charge of the intervention: The Operation Group representative: Name, signature and date 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): Signature and date RP name, signature and date

30 To ease interventions during breakdown or maintenance 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,

31 Radiation Protection Map 0,5 µsv/h < < 2,5 µsv/h > 2,5 µsv/h

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

33 OBJECTIVE: Injection with Front Ends open 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.

34 SOLUTIONS: Injection with Front Ends open 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.

35 Radiation monitor on every Beamline Control and Monitoring 100% of normalize dose: BL shutter closure 75% of normalize dose: Alarm 42 beamlines

36 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.

37 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)

38 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.