Material selection for TFTR limiters

Requirements for the material to be used as the first surface of limiters in TFTR are to (1) withstand a heat flux of 1 kW/cm2 for a pulse length of 1.5 s and a duty cycle of 1/200 for 105 cycles, (2) withstand the thermal and electromagnetic loads from 104 plasma current disruptions lasting about 200 μs, (3) generate impurities at a rate low enough to meet impurity control requirements (which depend on the atomic number of the material) for TFTR, and (4) have tritium retention characteristics consistent with tritium inventory requirements for TFTR. An extensive set of material tests using electron beams, neutral beams, and plasma bombardment have been carried out to identify materials which can meet the thermal requirements of (1) and (2) above. In most cases these tests have been combined with calculations of the expected thermomechanical response of the material to determine the reasons for the result observed. These studies have identified two major classes of materials which are acceptable: (1) graph...