light guide dosimeters and loss monitors
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
M. Körfer, DESY Salzau 22.01.20031
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 22.01.20032
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 22.01.20033
Light Guide Systems
Dosimeter Beam Loss
Powermeter
OTDR
Cerenkov Radiation Light Attenuation
Photomultiplier
Properties of fibers
MM GI FiberPhosphor-Doping Small annealing
MM SI FiberNo DopingLarge diameter
Detectors
Measurement
System
M. Körfer, DESY Salzau 22.01.20034
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 22.01.20035
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 22.01.20036
OTDR Measurement
OTDR: Tektronix TFP2A
Laser pulse duration: 3 ns (FWHM) at 850 nm local resolution 0.6 m
Optical Fiber : FiberCore N2900107GALinear attenuation up to 2000 Gy
TTF-fiber length < 300 m no laser pulse wideningdue 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 chamberto get fast results
M. Körfer, DESY Salzau 22.01.20037
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)
Fibre Length [m]
120 140 160 180 200 220
Do
se
[G
y(S
iO2)
]
0
100
200
300
400
500
140 160 180 200 220Fibrelength /m
12
14
16
18
20dezilamroN
thgilrewop
B/d
M. Körfer, DESY Salzau 22.01.20038
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
M. Körfer, DESY Salzau 22.01.20039
Powermeter Installation at TTF
• 5 - 20 Fiber windings around beam pipe • Dynamic range > 50 dB• Resolution: 140 mGy
Local Fibre Optic Radiation Sensor Systemfor the Undulator Magnets at TTF
Ethernet-box 100
ConcreteShielding
SwitchPCDESY
ComputerCentre
Data transfer to the FhG-INT
Newport 8800Optical Power Meter System
LEDSource
660 nm
1311
97
53
115
1 : 16Splitter
1412
108
64
216
Reference
1
16
UNDULATOR1
4
In
Out
Webserver
Beam
1
2
3
In
Out
5
6
7
10
9
8
UNDULATOR2
12
11
UNDULATOR3
M. Körfer, DESY Salzau 22.01.200310
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)
M. Körfer, DESY Salzau 22.01.200311
M. Körfer, DESY Salzau 22.01.200312
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
ACCELERATOR
FIBER OPTICAL CABLEIRRADIATION
PHOTODETECTOR
TIME MEASUREMENT
INTEGRATOR
INTENSITY
POSITION
Ext. Trigger
M. Körfer, DESY Salzau 22.01.200313
ACC1ACC2 BC2DUMP Region Cerenkov-Experiment GUN
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
M. Körfer, DESY Salzau 22.01.200314
Experiment at TTF1
M. Körfer, DESY Salzau 22.01.200315
Experiment at TTF1
M. Körfer, DESY Salzau 22.01.200316
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
M. Körfer, DESY Salzau 22.01.200317
Summary
Measurment-System:
OTDR Powermeter Cerenkov
Application Online local dose detection by averaging
Online local dose detection in real time
Online local dose detection in real time
Comment No single bunch resolution
No single bunch resolution
Single bunch resolution in a train
Detector response A few minutes A few ms A few ns
Range of dose [Gy] 3 – 450 limited by OTDR
0.14- 2000 limited by fiber
Not calculated yet
Range of wavelength [nm]
850 - 1330 860 200 – 850
Resolution length 1m 0.01 m 0.2 m
reasonable Fibre length*
5km 0.01 m 1km
* depending on max. dose and position resolution
M. Körfer, DESY Salzau 22.01.200318
Preliminary Test at TTF Undulator
Pulse-width (=spatial resolution) defined by
1) shower2) light-dispersion3) Electronic (PMT)
Zoom
2 loss position per bunch
M. Körfer, DESY Salzau 22.01.200319
M. Körfer, DESY Salzau 22.01.200320
Regeneration for fibers with temperature
Goal: Maintenance-free long-term use
Temperature 250 C 90 % regeneration within < 5 min
Indu
ced
Loss
[dB
/km
]
Time [s]
First irradiation
Second irradiation,after "regeneration"
M. Körfer, DESY Salzau 22.01.200321
Simulation and reconstruction of losses
M. Körfer, DESY Salzau 22.01.200322
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 TESLAGrundlagen und Abschlusbericht zum Forschungs- und Entwicklungsvertrag "Glasfaserdosimetrie fur TTF"H. Hensche, O. Kohn, S. Metzger, U. WeilandFraunhofer-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