Application of Infrared Thermography in NDT of Plasma-Facing Components for Tokamaks Pan QI, Qiang LI, Guang-Nan LUO Institute of Plasma Physics Chinese Academy of Sciences P.O.Box 1126, Hefei, China 17th World Congress of Non-Destructive Testing Exhibition Center, Shanghai, China, October 25 – 28, 2008 ASIPP

Outline Background Infrared thermography applied in PFCs testing R & D at ASIPP for NDT of PFCs Summary and future work

ASIPP Outline Background Infrared thermography applied in PFCs testing R & D at ASIPP for NDT of PFCs Summary and future work

Experimental Advanced Superconducting Tokamak (EAST) Background ASIPP International Thermonuclear Experimental Reactor (ITER) The background of my work is magnetic confinement fusion tokamak ITER being constructed in France The mini tokamak EAST constructed in our institute By the end of september 2006, the engineering missions were completed

The inner vacuum vessel with stainless- steel PFCs (initial phase) The inner vacuum vessel with graphite tiles PFCs (first phase) ASIPP The cross-section of EAST in-vessel components Divertors High field plate Passive plate Low field plate The vacuum vessel is the important part of tokamak. It contains divertors, passive plate, high field plate and low field plate. These parts make up of plasma facing components (PFCs). The components consist of plasma facing materials (PFMs) and Cu alloy heat sink. In the initial phase, stainless steel was used as PFM. Doped graphite tile is the main choice in the first phase (now) and tungsten will be chosen as candidate in the future phase. the purpose of PFCs is to protect the vacuum vessel, injection power system and diagnostic components.

ASIPP Problems of PFCs Engineering constraints Industrial constraints  bonding/joint  Ensure and control the quality of manufacturing (the keypoint for successful delivery of PFCs) (1) (1) M. Missirlian et al. Qualification of high heat flux components: application to target elements of W7-X divertor, in: 11 th PFMC, Greifswald, Germany,october11th, When tokamak is working, PFCs are the first wall facing plasma, subjected to high heat flux, bombardment of different particles and high magnetic filed. In this working conditions, PFCs will meet the problems, which contain engineering constraints and industrial constraints. But the transition (bonding/joint) between PFMs and heat sink is the most critical issue. How do we ensure and control the quality of this part during manufacturing is the key point for successful delivery of PFCs.

ASIPP Examination on quality of bonding/joint of PFCs Destructive methodNondestructive method  High heat flux(HHF) testing(very important) Purpose qualification of HHF PFCs design & modeling qualification of advanced nondestructive tests Method screening test-heat load limit fatigue test-fatigue limit critical heat flux test-safety margin for heat transfer  Metallography qualify the quality of the braze joint  Systematic fracture shear stress measurements qualify the quality of the braze joint  X-ray tomography - a sample X-ray examination allowed assessment of the different copper infiltration rates inside CFC tiles, which can change the global thermal conductivity of the HHF element  Ultrasonic inspection– applied to test the defect existing in PFMs/heat sink interface  Transient thermography – applied at the final stage of the fabrication and provide a global information about the thermal performance  Lock-in thermogaphy – applied to test PFCs throughout manufacturing process  Pulsed thermography – this approach is under development

ASIPP Comparison of the methods Methods HHF testUltrasonicX-ray testIR test Nondestructive NoYes Quantitative Yes conditional Test cost HighLowHighLow Portable NoYesNo decision by method

ASIPP Outline Background Infrared thermography applied in PFCs testing R & D at ASIPP for NDT of PFCs Summary and future work

ASIPP Transient thermography - SATIR Tank: hot water Control system (loop) Reference element Tested element Pump (SATIR : French acronym for Infra Red Acquisition and Data Processing Device) (1) In 1994,an infrared nondestructive test- bed SATIR was developed for the PFCs quality control by CEA (France fusion institute). The principle is based on the comparison of the surface temperature evolution between reference elements and tested elements during a transient heat load, which is generated by hot and cold water flowing successively in the cooling channel drilled in heat sink. Interface defects are detected by a slower temperature surface response. The surface temperature transition due to the heating and cooling cycle is measured by means of an infrared camera. The test-bed of SATIR

ASIPP This is the process of transient monitoring. The temporal evolution of the surface temperature difference at each corresponding pixel of both elements is calculated and the areal maxima (so-called DTref_max) distribution can be obtained. A bonding flaw between PFMs and heat sink can be judged from the distribution on the areas with the values of DTref_max higher than a critical value verified by high heat flux (HHF)testing. The disadvantage of the method is the necessity of a reference component. An innovative data processing based on spatial autocorrelation and on energy distribution at PFMs and heat sink bonding are being developed allowing inspection of a component without the necessity to get a reference component. Presence of defect (2) (2) A.Durocher et.al. Qualification and Nondestructive examination methods of high heat flux plasma facing components, in: the 24 th SOFT, Warsaw, Poland, Sept,12 th, 2006 No necessity of a reference component

ASIPP Manufacturing of calibrated flaws at the doped graphite tile/copper interface Trans.IR calibration and validation HHF test Transient validation (1)

ASIPP Lock-in thermography The Lock-in is a method based on propagation in the solids of modulated thermal waves imposed at the surface of element. It is used for evaluating the heat transfer capabilities of tiles, mainly the PFM/heat sink bonding Magnitude and phase-shift of surface temperature vary according to thermal properties underneath. Phase-shift is less sensitive to flux homogeneity and surface emissivity Properties: easy to operate, no cooling, less emissivity dependence Lock-in thermography device (movable) applied in TS Tokamak Investigations on possibility to detect damage during Tokamak shutdowns Features – Portable – In-field – Health check – Annual check – Global check – Suspicious tiles monitoring (1) (3) (3) X. Courtois et al, In-situ monitoring of actively cooled plasma facing components using acoustic and thermal methods, Phys. Scr. T128(2007)

ASIPP Pulsed thermography – ARGUS (Advanced infRared thermoGraphy Unit for inSpection) The ARGUS setup Principle : For each pixel, a frequency analysis based on the fast Fourier transform algorithm(FFT) is calculated on the cool down behavior after the flash. The defect detection is not based on the power spectrum of the FFT, but on the phase-shift of the basic frequency of the FFT(f1)and its higher harmonics(f2,f3,…). The basic frequency(f1) is adjusted to obtain a penetration depth reaching the foil/heat sink interface, whereas the penetration of the first harmonic frequency(f2) is limited to the PFM/foil interface. The means that the phase image of each frequency addressed by the FFT carries information about depth of the defect detected Application to AMC tiles inspection (4) (4) X. Courtois et al, In-situ monitoring of actively cooled plasma facing components using acoustic and thermal methods, Phys. Scr. T128(2007)

ASIPP Comparison of three thermography methods MethodsTrans.IRLock-in IRPulsed IR AimQuality control and the final acceptance test Technology maturityMatureImmature Reference element Yes No Data processingSimple and less dataComplex and large amount of data Equipment costsModerateCheap Test costsCheap Mass testingOk Quality criteriaQuantitative Determination of criteria Comparison of HHF calibration and complex PortableNo Yes

ASIPP Outline Background Infrared thermography applied in PFCs testing R & D at ASIPP for NDT of PFCs Summary and future work

ASIPP Construction of test-bed The experimental set-up at our institute Hot water tank Cold water tank Pump Infrared camera Tested sample Benefiting from the experience of SATIR, we have constructed the test-bed based on the method of transient thermography. Technical indicator Hot water flow rate: 3.9m/s Cold water flow rate:3.4m/s Hot water temperature:98 ℃ Cold water temperature:25 ℃ Volume of hot water tank:100L Volume of cold water tank:150L Infrared camera: ThermaCAM®PM595PAL, 320×240 pixels, 50 Hz

ASIPP HHF facility Max power: 10kW; accelerate voltage: 10kV; cooling water: 0.4MPa,2 m 3 /h; Max scanning area:>30 × 30mm The test equipment in ASIPP Technical indicator The results of NDE performed on the PFCs with calibrated defects must be compared with the high heat flux (HHF) test. So the facility is important and necessary for infrared thermography

ASIPP Infrared image with defect in flexible graphite layer Our works Simulation by ANSYS The IR image is used to visualize the heat transfer between the PFMs and heat sink, which enables to identify the calibrated defects in thermal contact. Three dimensional thermal finite element analyses have been performed to simulate the defect. The experimental observations obtained from IR thermography have confirmed the FE simulation.

ASIPP Edge detection for defect by canny operator

Outline ASIPP Background Infrared thermography applied in PFCs testing R & D at ASIPP for NDT of PFCs Summary and future work

ASIPP  Plasma-facing component is one of the most important in-vessel components in a tokamak. High reliability and stability are necessary for high performance plasma operations.  Good bonding/joint quality between the plasma-facing material and the heat sink is a keypoint to realize the high reliability and stability, which requires reliable examinations during manufacturing and at final batch reception.  Infrared thermography has proved to be a reliable and effective method in the examination and been chosen as a candidate method in the manufacturing of the ITER PFCs.  R & D work is underway to establish reliable NDTs in future manufacturing of the next- step EAST PFCs, mainly including IR thermography and ultrasonic inspections. Summary

ASIPP Future work  Continuous efforts in developing IR transient thermography NDT, i.e., completion and improvement of the system, esp. calibration with comparison to HHF testing  More NDT methods, e.g., ultrasonic inspection, will be examined for their use in the manufacturing of the future EAST PFCs  The acceptance criteria for the NDTs must be determined via dedicated and reliable testings, usually destructive ones  Portable Lock-in or Pulsed IR thermography test-bed will be useful for in-field examination, may be used as an effective tool for routine health check and service life prediction of the PFCs

ASIPP