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Light guide dosimeters and loss monitors

Light guide dosimeters and loss monitors. H. Henschel, J . Kuhnhenn Fraunhofer-Gesellschaft INT M. Körfer , K. Wittenburg DESY F. Wulf Hahn-Meitner-Institut HMI. Motivation. Sensor for continuous online-monitoring of radiation sensitive components (Undulator, Electronics)

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Light guide dosimeters and loss monitors

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  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 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: M. Körfer, DESY Salzau 22.01.2003

  3. Light Guide Systems System Dosimeter Beam Loss Light Attenuation Cerenkov Radiation Measurement MM GI Fiber Phosphor-Doping Small annealing MM SI Fiber No Doping Large diameter Properties of fibers OTDR Detectors Photomultiplier Powermeter 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 radiationindependent from dose-rate and -source 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 M. Körfer, DESY Salzau 22.01.2003

  6. Installation of fibers along the vacuum chamber to get fast results 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 M. Körfer, DESY Salzau 22.01.2003

  7. 20 B /d r 18 e w o p 16 t h g i l 14 d e z i l 12 a m r o N 140 160 180 200 220 Fibre length /m ACC2 ACC1 ACC3 COL BC2 INJ 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) M. Körfer, DESY Salzau 22.01.2003

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

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

  11. M. Körfer, DESY Salzau 22.01.2003

  12. Ext. Trigger 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-wavelength200 nm -700 nm (I ~ 1/3) -- Integral of light pulse is proportional to dose M. Körfer, DESY Salzau 22.01.2003

  13. DUMP Region Cerenkov-Experiment ACC2 BC2 ACC1 GUN fiber  Cerenkov Radiation BLPM* * Beam loss position monitor Goal: Fast transversal & long. beam loss profile monitoring Cross-Section of beam pipe an fiber position Y X M. Körfer, DESY Salzau 22.01.2003

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

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

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

  17. Summary 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 M. Körfer, DESY Salzau 22.01.2003

  19. M. Körfer, DESY Salzau 22.01.2003

  20. Regeneration for fibers with temperature Goal: Maintenance-free long-term use Temperature 250 C90 % regeneration within < 5 min M. Körfer, DESY Salzau 22.01.2003

  21. Results of reconstruction: Simulation and reconstruction of losses 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 TTFTESLA-Report No. 2000-25 August 2000 H. Henschel, M. Körfer, K. Wittenburg, F. Wulf Fiber Optic Radiation Sensing Systems for TESLATESLA 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 M. Körfer, DESY Salzau 22.01.2003

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