A Fast-Response Thermocouple for Temperature Fluctuation Measurements in Sodium Coolants

A special Chromel/Alumel thermocouple was fabricated whereby the bare ends of the wires were fixed ∼1 mm apart. In a medium with a good electrical conductivity (e.g., liquid sodium), the junction of this thermocouple is replaced by the medium itself. Hence, a fast undelayed response is expected. While mean temperature data of this device are in good agreement with data for conventional thermocouples, power spectral densities of the open element contain contributions from much higher frequencies than those of conventional thermocouples.