## 2 Real-Time Measurement System  
### Measurement Technique  
It is difficult to measure ion optics deformation and grid gap variation that are caused by plasma radiation and power deposition, and this paper applies the videometrics measurement method to achieve noncontact measurement of ion optics deformation and grid gap variation. Ion optics works in a vacuum environment accompanied by a high temperature and plasma. In this complex and extreme environment, common thermal deformation measurement methods cannot be used. At the same time, ion optics deformation and grid gap variations are small, so the requirement of measurement accuracy is very high, which is to be in the order of 10 \(\upmu\)m. We used a telemicroscope to obtain high-magnification images, and then employed a subpixel image processing algorithm to achieve high-precision measurement of the microdeformation. This noncontact measurement method can avoid grid surface high-temperature effects on the ion optics deformation measurement, and with the protection devices, the measurement system can work properly in vacuum and plasma environments.  
The core idea is to install probes and cooperative targets on ion optics and indirectly measure the ion optics deformation by using displacements of the cooperative targets. The cooperative target is a G10 class zirconia sphere with a diameter of 1.5 mm and a precision of 0.25 \(\upmu\)m. The probe is an alumina cylinder with a variable diameter structure. As shown in Figure 1, two probes were fixed to the center hole of the screen grid and the accelerator grid, and the cooperative targets were fixed to the center hole of the decelerator grid, and the top of the probes. The probes and the cooperative targets were fixed with high temperature glue. In addition, the probes with a snap structure and thread structure can also be selected in the installation scheme.  
Measuring positions were the center of the screen grid, the accelerator grid, and the decelerator grid (maximum deformation of grid). The physical quantities that were measured were the displacements of three cooperative targets. The telemicroscope was mounted on the side of the ion optics through a four-axis precise positioning platform. The devices were adjusted to place the probes and cooperative targets in the middle of the field. The horizontal displacements of three cooperative targets in the field of view represent the thermal deformation of three grids of ion optics. The change in the grid gaps was equal to the difference in thermal deformation of the three grids. When starting the measurement, the serial images collected by the telemicroscope were transmitted to the computer in real time, and the edges of the cooperative targets were extracted by the image processing algorithm. Based on the edge of the cooperative targets, the coordinates of the center of the circle were fitted by the least squares method to accurately locate the cooperative targets, and the image magnification factor and the rotation angle of the coordinate system were also calibrated at the same time. The deformation of the three grids was calculated by the displacements of the cooperative targets, and the variations of the grid gaps were calculated from the difference between the three grids' thermal deformation in real time.  
Figure 1: The installation of probes and cooperative targets.