1. M. Körfer, DESY Salzau 22.01.2003 1 Light guide dosimeters and loss monitors H. Henschel, J. Kuhnhenn Fraunhofer-Gesellschaft INT M. Körfer, K. Wittenburg DESY F. Wulf Hahn-Meitner-Institut HMI

2. M. Körfer, DESY Salzau 22.01.2003 2 Motivation Sensor for continuous online-monitoring of radiation sensitive components (Undulator, Electronics) accelerator sections with spatial resolution fast beam losses Dosimetry in small and tiny spaces Insensitive to electromagnetic fields Maintenance free operation Three different systems have been studied:

3. M. Körfer, DESY Salzau 22.01.2003 3 Light Guide Systems DosimeterBeam Loss Powermeter OTDR Cerenkov RadiationLight Attenuation Photomultiplier Properties of fibers MM GI Fiber Phosphor-Doping Small annealing MM SI Fiber No Doping Large diameter Detectors Measurement System

4. M. Körfer, DESY Salzau 22.01.2003 4 Dosimeter Fiber: Optical fibers show (wavelength-dependent) a nearly linear increase of attenuation after irradiation with ionizing radiation independent from dose-rate and -source

5. M. Körfer, DESY Salzau 22.01.2003 5 OTDR Goal: Continuous Online-Measurement of the local dose (e.g. along the LINAC) Radiation creates color-centers in fiber  Measurement of the attenuation with OTDR -- short Laser pulse enters the light guide -- Rayleigh Scattering reflects light back to detector -- Color centers absorb backscattered light -- Absorption is proportional to the dose

6. M. Körfer, DESY Salzau 22.01.2003 6 OTDR Measurement OTDR: Tektronix TFP2A Laser pulse duration: 3 ns (FWHM) at 850 nm  local resolution 0.6 m Optical Fiber : FiberCore N2900107GA Linear attenuation up to 2000 Gy TTF-fiber length < 300 m  no laser pulse widening  due to the fiber bandwidth the local resolution along the accelerator is constant Dynamic range about >12 dB @ 850 nm  limitation of the max. dose and length Installation of fibers along the vacuum chamber to get fast results

7. M. Körfer, DESY Salzau 22.01.2003 7 Results - OTDR Time period 17 Day’s in 11/2000 Beam direction from the right dynamic range limits observation of max. dose and max. length  noisy signal in the injector region (INJ) Dose budget: Bunch compressor BC2 up to 450 Gy temp. Beam-line ACC3 up to 200 Gy above 180 m the noise starts resolution < 3 Gy (noise limit)

8. M. Körfer, DESY Salzau 22.01.2003 8 Powermeter Goal: Precise, sensitive and fast online-dosimetry -- light from Laser LED enters the light guide -- continuous measurement of the light power (attenuation) -- position of sensor defines spatial resolution Radiation creates color-centers in fiber  Measurement of the attenuation with Powermeter calibration

9. M. Körfer, DESY Salzau 22.01.2003 9 Powermeter Installation at TTF 5 - 20 Fiber windings around beam pipe Dynamic range > 50 dB Resolution: 140 mGy

10. M. Körfer, DESY Salzau 22.01.2003 10 Comparison with TLD Measurements Deviation: mostly < 25 % Reasons: not same position TLD Error 10-20 % Smoothed accumulated dose (2001-11-26 to 2002-01-21)

11. M. Körfer, DESY Salzau 22.01.2003 11

12. M. Körfer, DESY Salzau 22.01.2003 12 Cerenkov Radiation Goal: Fast beam loss monitor with spatial resolution -- ionizing radiation creates Cerenkov light in ps-range -- Time difference between external bunch trigger and light pulse defines position -- Broadband detector (  GHz), high sensitivity, low noise => PMT, APD -- Photon-wavelength 200 nm -700 nm (I ~ 1/ 3 ) -- Integral of light pulse is proportional to dose Ext. Trigger

13. M. Körfer, DESY Salzau 22.01.2003 13 ACC1ACC2BC2DUMP RegionCerenkov-ExperimentGUN X Y fiber  Cross-Section of beam pipe an fiber position Cerenkov Radiation BLPM* Goal: Fast transversal & long. beam loss profile monitoring * Beam loss position monitor

14. M. Körfer, DESY Salzau 22.01.2003 14 Experiment at TTF1

15. M. Körfer, DESY Salzau 22.01.2003 15 Experiment at TTF1 Results of reconstruction: 

16. M. Körfer, DESY Salzau 22.01.2003 16 Cerenkov Radiation BLPM* TTF2 Prototype Undulatorkammer Goal: Fast transversal & long. beam loss profile in the TTF2 Undulator 4 fibers close to beam x Y fibers groove  * Beam loss position monitor

17. M. Körfer, DESY Salzau 22.01.2003 17 Summary

18. M. Körfer, DESY Salzau 22.01.2003 18 Preliminary Test at TTF Undulator Pulse-width (=spatial resolution) defined by 1) shower 2) light-dispersion 3) Electronic (PMT) Zoom 2 loss position per bunch

19. M. Körfer, DESY Salzau 22.01.2003 19

20. M. Körfer, DESY Salzau 22.01.2003 20 Regeneration for fibers with temperature Goal: Maintenance-free long-term use Temperature 250  C 90 % regeneration within < 5 min

21. M. Körfer, DESY Salzau 22.01.2003 21 Simulation and reconstruction of losses Results of reconstruction:

22. M. Körfer, DESY Salzau 22.01.2003 22 References FIBRE OPTICAL RADIATION SENSING SYSTEM FOR TESLA H. Henschel, Fraunhofer-INT, Euskirchen, Germany, M. Körfer, DESY, Hamburg, Germany, F.Wulf, HMI, Berlin, Germany 5th European Workshop on Diagnostics and Beam Instrumentation, DIPAC, Grenoble 2001 Faseroptische Strahlundgssensoren fur TESLA Grundlagen und Abschlusbericht zum Forschungs- und Entwicklungsvertrag "Glasfaserdosimetrie fur TTF" H. Hensche, O. Kohn, S. Metzger, U. Weiland Fraunhofer-Institut fur Naturwissenschaftlich-Technische Trendanalysen (INT) Interner Bericht 4/01, August 2001 H. Henschel, O. Köhn, M. Körfer, Th. Stegmann, F. Wulf Preliminary Trials with Optical Fiber Dosimeters at TTF TESLA-Report No. 2000-25 August 2000 H. Henschel, M. Körfer, K. Wittenburg, F. Wulf Fiber Optic Radiation Sensing Systems for TESLA TESLA Report No. 2000-26 September 2000 Optical Fiber Dosimetry at the Tesla Test Facility (TTF) H. Henschel, O.Köhn, M. Körfer, T. Stegmann, K. Wittenburg, F. Wulf 9th Beam Instrumentation Workshop Royal Sonesta Hotel Boston, 5 Cambridge Parkway, Cambridge, MA USA, May 8-11, 2000