Temperature Measurements of Limiter Surfaces at High Heat Flux in the HT-7 Tokamak H. Lin, X.Z. Gong, J. Huang, J.Liu, B. Shi, X.D. Zhang, B.N. Wan, J.G. Li and the HT-7 Team Institute of Plasma Physics, Chinese Academy of Sciences P.O.Box 1126, Hefei, Anhui 230031, P.R.China *E-mail: auhui@ipp.ac.cn 17th PSI, Hefei, Anhui, China, May 22-26, 2006

17th PSI, Hefei, Anhui, China, May 22-26, 2006 Outline Introduction Infrared Camera System: ThermaCAMTM 595 Estimation of heat flux at limiter surface Calculated by edge conditions Temperature measurements Simulated by solving the 3-D heat conduction equation (ANSYS code) Experimental results and discussion Summary 17th PSI, Hefei, Anhui, China, May 22-26, 2006

17th PSI, Hefei, Anhui, China, May 22-26, 2006 Introduction HT-7---medium-sized, actively water-cooled up-down symmetric toroidal limiters & belt limiters located at high field side (HFS). Main goals: steady-state operation study relevant techniques and underlying physics ---Doped graphite GBST1308: 1%B, 2.5%Si, 7.5%Ti, with a SiC gradient coating: 100μm An increase of plasma density with higher injected and radiated energies during long pulse operation, correlated with C 、O and H recycling increase. Measure the limiter’s surface temperature: inferring the local heat flux deposition on the limiters limiting the heat load on the leading edge 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Infrared Thermography System Limiters and Liners Observation of LHW Antenna and Samples Side View Thermocouples General specifications： Frequency 50/60Hz Thermal sensitivity <0.10C Spectral range 7.5-13μm Detector type: 320×240 pixels Measurement range: -400C-+20000C Lens/Focus/HFOV: 240/0.5m/0.2m Doped graphite tile Thermocouples meter Stainless Steel heat sink 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Estimation of heat flux at limiter surface (I) Te , ne can be measured by Langmuir probe Fig. 4. Boundary profiles compared for discharges with (closed) and without (open) IBW and LHCD: (a) electron density, (b) electron temperature. 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Estimation of heat flux at limiter surface (I) From sheath model the power flux P to the limiter surface If assume For HT-7: Discharges with IBW and LHCD: P= 1.73MW/m2 Discharges without IBW and LHCD: P= 1.14MW/m2 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Estimation of heat flux at limiter surface (II) Simulated by solving the 3-D heat conduction equation (ANSYS code) The power flux deposited on test limiter is calculated by solving the non-stationary heat conduction equation with the measured time dependent surface temperatures as boundary conditions. - the calculation is done with 3D finite element code –ANSYS - test limiter is assumed to be thermally isolated - radiation loss is omitted - temperature dependent conductivity and heat capacity - results can be compared with thermocouple data processing 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Heat flux in long pulse discharges In a LHCD discharge, as increasing of injected energy and plasma duration, the deposition of large energy flux on the first wall, leading to the global recycling increases to and above unity with carbon and oxygen impurities increasing. 17th PSI, Hefei, Anhui, China, May 22-26, 2006

Heat deposition pattern correlated to plasma displacement Spot1 Spot2 17th PSI, Hefei, Anhui, China, May 22-26, 2006

#80720 #80721 #80722 Corresponding IR Images When the plasma vertical displacement was adown, parts of the lower toroidal limiters represented higher temperature. v.v. 17th PSI, Hefei, Anhui, China, May 22-26, 2006

The highest temperature on the belt limiter @ HFS The rapid increasing of local temperature in carbon tiles led to high carbon erosion yield and self-sputtering yield, which caused huge erosion and RES and induced carbon bloom. Then carbon penetrated into the plasma and resulted in immediately plasma collapse. 17th PSI, Hefei, Anhui, China, May 22-26, 2006

17th PSI, Hefei, Anhui, China, May 22-26, 2006 Surface analysis IBW antenna Deposition Ion side Strongly eroded The erosion of the surface was estimated to be 8.9nm/1s (a whole campaign). The surface of all tiles was covered by higher concentration metal impurities that probably came from plasma interacting with lower hybrid wave (LHW) antenna, which is made of stainless steel. 17th PSI, Hefei, Anhui, China, May 22-26, 2006

17th PSI, Hefei, Anhui, China, May 22-26, 2006 Summary Two methods of estimation of heat flux at limiter surface --- Te & ne or Tthermocouples &TIR ---ANSYS code In LHCD discharges: ---PLHCD  deposited energy flux (or surface temperature) on the limiter Heat deposition pattern was correlated to the plasma displacement. High erosion on the leading edge (ion drift side@HFS) ---The supra-thermal electron and fast particles (by LHCD) interacting with the local region of the limiters. Impurity injection ---heat load reduced by radiation edge layer, corresponding surface temperature reduction. PMI&Surface analysis 17th PSI, Hefei, Anhui, China, May 22-26, 2006