An ultra-fast X-ray computed tomography (CT) scanner has been developed for measurement of gas-liquid two-phase flow. This scanner overcomes problems that occur in a transient or unsettled state, which make the conventional CT scanner inappropriate. To reduce the scanning time, this X-ray CT system uses electronic switching of electron beams for X-ray generation instead of the mechanical motion adopted by conventional CT scanners. A prototype system with a scanning time of 3.6 milliseconds was initially developed and confirmed to measure the dynamic events of two-phase flow. However, an increased scanning speed is generally required for practical use in the thermal-hydraulics research field. Therefore, an advanced type which can operate under the scanning time of 0.5 milliseconds and can measure two-phase flow with a velocity up to 4-5 m/s was developed.
