Cherenkov Detector

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Cherenkov Detector for Fusion Power Monitoring
Yury Verzilov and Takeo Nishitani Moscow
Engineering Physics Institute, Russia FNS,
Japan Atomic Energy Agency, Japan
Neutron WG Meeting, 10 ITPA, April 11, 2006,
Moscow, RUSSIA
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Research Motivation

• Development of a Neutron Monitoring System
• Providing an alternative method compare to
  Systems based on a Fission Chamber
• Sensitive to Virgin D-T Neutrons
• Combining NAM advantages with Temporal
  Resolution Ability
• Basing on a Light Processing Technology.
• Progress in Fiber Optic Development

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Outline

• Two fusion power monitor approaches based on
  activation of flowing water
• Proof-of-approach experiment
• Designing a water Cherenkov radiator with fiber
  readout systems
• Testing detectors inside and outside the D-T
  neutron source limits
• Evaluating temporal parameters
• Concept of the Cherenkov Monitor for ITER

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Water Activation in a Fusion Environment Two
Approaches for Registration
16O(n,p)16N - Dominant activation reaction Major
b-decay branches of 16N (T1/2 7.13 s)
16N
Registration by Cherenkov detector
10.4 MeV
Ebgt0.26MeV
4.8
b-rays
7.1 MeV
66
6.1 MeV
Water
g-rays
28
Registration by Scintillator
0 MeV
16O
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Fusion Power Monitor Based on Activation of
Flowing Water
Water transfers the Neutron Pulse Information to
the remote Detector

• Disadvantages
• Insufficient time resolution
• Time delay
• Location of the remote detector is limited

Registration of g-rays (Eg 6.1 and 7.1 MeV)
Present Technique
BGO g-Detector e 10
D-T Plasma Pulse

• Advantages
• Good time resolution
• Absence of Time delay
• The remote detector may be located anywhere

Optical Fiber
Cherenkov Detector emax 90
Cherenkov Light by b-rays from 16N (Emax10.4
MeV)
Proposed Technique
Light transfers the Neutron pulse Information to
the remote Detector
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Theoretical Aspects of the Cherenkov Detector
(non-focusing type)
PMT response Cherenkov spectrum Quantum
efficiency of the PMT
Intensity (relative value)
Wavelength (nm)
Photon yield of electrons in water for region of
300-600 nm
Electron energy (MeV)
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PMT Response to Cherenkov Photons from b-rays of
16N and 32P in water
100 Light collection
16N 4290 keV / 66.2 10420 keV / 28.0
2 Light collection
Intensity (relative value)
32P 1709 keV / 100 Ebmax / Ib
Channel
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Water Cherenkov Detector with Wavelength-Shifting
(WLS) Fiber Readout
Reflector
WLS fiber
Quartz tube
Water flow
WLS fiber twined round the quartz tube
Clear fiber bundle
to PMT
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Experimental Setup for Measurement of Detector
Parameters
D-T Neutron Source
Detector position A
3.5 m
Target room
Shielding
Measurement room
8.9 m
Detector position B
Pump
Flow meter
Water reservoir
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Water Cherenkov Detector with WLS Fiber Readout
(Outside the D-T Source Limits)
V H2O flow 2 cm/sec
Neutron Pulse / Detector response

• Tests with pulsed and direct D-T neutron modes
  were completed
• Detector has demonstrated reasonable
  characteristics of
• light collection efficiency
• temporal resolution.
• Temporal resolution of the detector can be
  improved by increasing water flow velocity
• Detector can not be used around the D-T source,
  due to high g-sensitivity of WLS fiber
• New Design of the detector with quartz fiber is
  proposed.

Intensity (relative value)
V H2O flow 10 cm/sec
Time (s)
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Water Cherenkov Detector with a Quartz Fiber
Readout
SS tube
Reflector
Water flow
Quartz Fiber bundles
to PMT
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Water Cherenkov Detector with Quartz Fiber Readout
Water Flow
Quartz Fiber Bundle

• Designs and the experimental setup are not
  optimized for best performance
• Main objective
• Gain experimental data that will serve as a basic
  guideline for further elaboration upon detector
  development.

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Detector Response to the Pulsed Neutron Flux
(Outside the D-T source limits)
Detector Position B (8.9 m) Pulsed Mode step -
20 sec duty 50 V H2O flow 1.67 m/sec
Neutron Pulse Ideal Response Detector Response
Delay
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Detector Response to the Pulsed Neutron Flux
Experiment Calculation (Based on the laminar flow
model)
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Time Spectrum for the Detector located inside the
D-T Source Limits
H2O flow 4 L/min
H2O flow 0 L/min
A and B - the chance coincidence rate of
uncorrelated events, when fiber bundles were
connected and then disconnected from the
radiator. C - the coincidence rate of correlated
events from the 16N decay.
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Detector Response to the Pulsed Neutron Flux
(Inside the D-T source limits)
V H2O flow 0.08 m/s
Neutron Pulse Detector Response
B
A
C
V H2O flow 0.26 m/s
Intensity (relative value)
Response components A - Prompt source gamma B
- Prompt source gamma 16N C - 16N
Time (s)
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Concept of the Neutron Monitor based on Cherenkov
Light for ITER
Vacuum Vessel 75cm
First Wall Blanket 40cm
Parameters Delay 0 sec Resolution 10 ms
D-T Plasma
H2O Radiator (D-2.5cm, L-5cm) VH2O flow 5 m/s
Quartz Fiber Bundle
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Conclusion

• Cherenkov Detector has demonstrated the ability
  to work properly in a radiation environment
• Temporal detector parameters can be improved by
  optimizing the Cherenkov detector design
• The present study elaborates upon the
  feasibility and effectiveness of utilizing the
  Cherenkov Detector as a Fusion Power Monitor with
  activation of flowing water.