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

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

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

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

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

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 300-600 nm Electron energy (MeV)

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

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

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

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)

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

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.

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

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

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.

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)

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

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.