1. for Fusion Power Monitoring
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

2. Development of a Neutron Monitoring System:
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

3. 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

4. 16O(n,p)16N - Dominant activation reaction
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
Eb>0.26MeV
4.8%
b-rays
7.1 MeV
66%
6.1 MeV
Water
28%
g-rays
Registration by Scintillator
16O
0 MeV

5. 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
Present Technique
Registration of g-rays (Eg = 6.1 and 7.1 MeV)
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 (Emax=10.4 MeV)
Proposed Technique
Light transfers the Neutron pulse Information to the remote Detector

6. Photon yield of electrons in water for region of 300-600 nm
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 nm
Electron energy (MeV)

7. PMT Response to Cherenkov Photons from b-rays of 16N and 32P in water
100% Light collection
16N
4290 keV / 66.2%; keV / 28.0%
2% Light collection
Intensity (relative value)
32P
1709 keV / 100% {Ebmax / Ib}
Channel

8. WLS fiber twined round the quartz tube
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

9. Experimental Setup for Measurement of Detector Parameters
Detector position A
D-T Neutron Source
3.5 m
Target room
Shielding
Measurement room
8.9 m
Detector position B
Pump
Flow meter
Water reservoir

10. Neutron Pulse / Detector response
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)

11. Water Cherenkov Detector with a Quartz Fiber Readout
SS tube
Reflector
Water flow
Quartz Fiber bundles
to PMT

12. 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.

13. 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

14. Detector Response to the Pulsed Neutron Flux
Experiment
Calculation (Based on the laminar flow model)

15. 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.

16. 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)

17. Concept of the Neutron Monitor based on Cherenkov Light for ITER
First Wall
& Blanket
~ 40cm
Vacuum
Vessel
~ 75cm
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

18. 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.