Evaluation of applicability of laser-based distance meter to measure Li-jet thickness for IFMIF/EVEDA project

Abstract

A technique was needed for measuring the thickness of the liquid lithium target of the International Fusion Materials Irradiation Facility (IFMIF11IFMIF, International Fusion Materials Irradiation Facility; EVEDA, Engineering Validation and Engineering Design Activities; MFD, mode field diameter; TOF, time-of-flight; A/D, analog-to-digital.). Thus, the applicability of a laser-based distance meter was evaluated within the framework of Engineering Validation and Engineering Design Activities (EVEDA) of IFMIF. This device is usually used against diffuse objects. However, in the present case, it is used against specular, finely deformed liquid metal surfaces. Both the measurement resolution and precision are required to be 0.1mm or less to measure the thickness variation of ±1mm. To ensure sufficient power of the reflected laser from the liquid metal surface, the laser spot diameter was set to 0.1mm, considering previous experimental data regarding the dominant wavelength of surface waves. An experiment was conducted at the Osaka University Li loop in the velocity range 10–15m/s and Li temperature of 300°C under an argon atmosphere of 0.12MPa. The experimental results showed that the laser-based distance meter can be used to measure the Li-jet thickness at a jet velocity of up to 15m/s and with superior precision at 16μm, which is a much more precise value than required.