Laser interferometric quadrature phase method for tokamak wall surface vibration measurements

In order to realize the in-situ diagnosis of the surface morphology of Plasma-Facing materials (PFMs) in advanced superconducting tokamaks, such EAST, Dalian University of Technology has developed the Speckle Interference Experiment Platform (DUT-SIEP). In order to ensure high resolution, DUT-SIEP introduces a vibration-sensitive time phase-shifting technique. The influence of environmental vibration leads to a decrease in the accuracy of surface topography measurement for PFMs. Therefore, it is very important to in-situ characterize the vibrational parameters of tokamak device for vibrational disturbance compensation in PFMs surface topography measurement. To this issue, we propose an approach based on Laser Interferometric Quadrature Phase (LIQP) method for measurement of vibrational parameters of tokamak wall for improving the accuracy of surface topography measurement by compensating the phase error introduced by vibration disturbance. The vibration measurement is performed by obtaining two vibrational interferometric signals with phase difference due to the difference of the distance from two photodiodes to the beam splitter mirror, and correcting them to two signals with orthogonal phase difference by the least squares method. By using the inverse tangent calculation and phase unwrapping of the two orthogonal signals, the displacement of the vibrating target is reconstructed in real time. In order to simulate the actual working conditions of the EAST tokamak device, the amplitude and frequency measurements of different vibrations are carried out under the experimental conditions of a three-meter far field. The experimental results demonstrate the potential application of this method in the in situ measurement vibrational parameters of tokamak devices.