1. 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 , P.R.China
* th PSI, Hefei, Anhui, China, May , 2006

2. 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 , 2006

3. 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 , 2006

4. 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 μm
Detector type: 320×240 pixels
Measurement range: -400C C
Lens/Focus/HFOV: 240/0.5m/0.2m
Doped graphite tile
Thermocouples
meter
Stainless Steel heat sink
17th PSI, Hefei, Anhui, China, May , 2006

5. 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 , 2006

6. 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 , 2006

7. 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 , 2006

8. 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 , 2006

9. Heat deposition pattern correlated to plasma displacement
Spot1
Spot2
17th PSI, Hefei, Anhui, China, May , 2006

10. #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 , 2006

11. 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 , 2006

12. 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 , 2006

13. 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
---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 , 2006