Development of a Quick-Response Microwave Bolometer for the Stray Radiation Measurement in LHD

A quick-response microwave bolometer has been developed to measure the stray radiation during ECRH in LHD. A prototype installed in the ECRH antenna port can respond within 15 ms after the starting of the power input. With taking into account the humming noise and irregular voltage fluctuations coming into the signal line, the stray radiation that causes the temperature increase of the microwave absorber more than 0.1 degrees for more than 50 ms is detectable. The power flux of 28 kW/m
²
is required to discriminate the stray radiation from the voltage fluctuations within 50 ms.