EXAMINATION OF MATERIAL PERFORMANCE OF W EXPOSED TO HIGH HEAT LOAD - POSTMORTEM ANALYSIS OF W EXPOSED TO TEXTOR PLASMA AND E-BEAM TEST STAND

摘要

We have examined the behavior of high Z limiters exposed to TEXTOR edge plasma and found that under certain conditions high Z materials are compatible with plasmas. In high density Ohmic plasmas the accumulation of a high Z impurity in the plasma center with significant radiation is observed, whereas an auxiliary heating like NBI and ICRH enhances the impurity exhaust with saw tooth activity. For a practical use of high Z plasma facing materials, extremely high heat load from the plasma becomes a serious concern. In the present work we have conducted the high heat load tests of tungsten (W) using two different heat sources, one is the W limiter exposed to TEXTOR plasma and tile other is various W samples heat loaded with an intense E-beam using the JEBIS facility in Japan Atomic Energy Research Institute (JAERI). From the test results we have to conclude that W, if applied in the form of the bulk material, should be used above the ductile brittle transition temperature (DBTT) but below about 1500 degrees C to avoid the recrystallization. Maximum heat load tolerable without surface melting is about 20 MW/m(2) for several seconds, The monocrystalline used at high temperatures shows very good performance, though the production of the monocrystalline with a desired shape is not easy, Considering its brittle nature, hard machining and heavy mass, bulk W cannot be a structure material but be used as a thin tile or deposited film on some structure materials. Unfortunately, however, the thermal expansion coefficient of W is so small that brazing of W to a heat sink material like Cu which has a much larger thermal expansion coefficient would easily result in cracking due to the large thermal stress. Thus the development of tungsten plasma facing component (PFC) needs much effort in future. [References: 11]