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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. Motivation. Sensor for continuous online-monitoring of radiation sensitive components (Undulator, Electronics)

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slide1

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

motivation
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

light guide systems
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

slide4

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

slide5

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

otdr measurement

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

slide7

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

powermeter
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

powermeter installation at ttf
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

comparison with tld measurements
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

cerenkov radiation

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

slide13

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

experiment at ttf1
Experiment at TTF1

M. Körfer, DESY Salzau 22.01.2003

experiment at ttf11

Results of reconstruction:

Experiment at TTF1

M. Körfer, DESY Salzau 22.01.2003

cerenkov radiation blpm

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

summary
Summary

M. Körfer, DESY Salzau 22.01.2003

slide18

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

regeneration for fibers with temperature
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

slide22

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