Thermal output response analysis on the thermocouples in the beam limiters for the JT-60 NBI drift duct

Thermal output response analysis on the thermocouples in the beam limiters for the JT-60 NBI drift duct was performed. The thermocouple are set up to measure the axis displacement of extracted beams and to protect the beam limiters against the neutral beam. Each thermocouple is inserted to a hole in the beam limiter. Hence, the thermal contact resistance between the thermocouple and the beam limiter may be changed according to the magnitude of the spring back force. We have evaluated experimentally the thermal contact resistance between the thermocouple and the beam limiter by introducing the effective thermal conductivity of combined thermal contact resistance and the characteristic thermal resistance of the thermocouple. The experiments clarified that the effective thermal conductivity λ varies from 4.2 x 10-3 to 2.66 x 10-2 W/m deg C. Using the result, we have simulated numerically the thermocouple output response when the beam limiters recives the pulsed neutral beam. The result indicates that we can estimate the maximum temperature and heat loading of the beam limiter within the error range ± 30 % by measuring the data after 120 sec from beam off. (author)