Inhomogeneous heat loading to high-Z test limiters depending upon the limiter materials

The change in the temperature distribution was investigated for different target materials by inserting a Ta/W twin limiter into TEXTOR edge plasmas. Depending upon the limiter material and the limiter location, the position of the maximum temperature on the limiter surface changed. A three-dimensional heat transfer calculation taking the radiation loss from the surface into account was conducted to find out the factors governing the heat flux onto the test limiter. The result for the Ta test limiter shows that the experimentally observed temperature asymmetry in the toroidal direction can be explained if the plasma heat flux decreases exponentially from the last closed flux surface with the e-folding length of the ion drift side about 50% longer than that of the electron drift side. The intensity of Dβ light around the ion drift side of the limiter was larger than that at the electron drift side by about 30%, corresponding with a larger particle flux to the ion drift side.