Light guide dosimeters and loss monitors

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Light guide dosimeters and loss monitors
H. Henschel, J. Kuhnhenn Fraunhofer-Gesellschaft
INT M. Körfer, K. Wittenburg DESY F.
Wulf Hahn-Meitner-Institut HMI
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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
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Light Guide Systems
Dosimeter
Beam Loss
System
Cerenkov Radiation
Light Attenuation
Measurement
MM GI Fiber Phosphor-Doping Small annealing
MM SI Fiber No Doping Large diameter
Properties of fibers
OTDR
Photomultiplier
Detectors
Powermeter
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Dosimeter FiberOptical fibers show
(wavelength-dependent) a nearly linear increase
of attenuation after irradiation with ionizing
radiationindependent from dose-rate and -source
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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
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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 lt 300 m
• ? no laser pulse widening
• due to the fiber bandwidth the local
• resolution along the accelerator is constant
• Dynamic range about gt12 dB _at_ 850 nm
• ? limitation of the max. dose and length

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Results - OTDR
Time period 17 Days 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 lt 3 Gy (noise limit)

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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
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Powermeter Installation at TTF

• 5 - 20 Fiber windings around beam pipe
• Dynamic range gt 50 dB
• Resolution 140 mGy

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Comparison with TLD Measurements
Smoothed accumulated dose (2001-11-26 to
2002-01-21)
Deviation mostly lt 25

• Reasons
• not same position
• TLD Error 10-20

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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 gt PMT, APD -- Photon-wavelength 200 nm
-700 nm (I 1/?3) -- Integral of light pulse is
proportional to dose
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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
 
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Experiment at TTF1
 
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Experiment at TTF1
Results of reconstruction  
?
 
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Cerenkov Radiation BLPM
Beam loss position monitor
Goal Fast transversal long. beam loss profile
in the TTF2 Undulator
TTF2 Prototype Undulatorkammer
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Summary
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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
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Regeneration for fibers with temperature
Goal Maintenance-free long-term use
Temperature 250 ?C 90 regeneration
within lt 5 min
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Simulation and reconstruction of losses
Results of reconstruction  
 
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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