## 4 Instrument Design
### Detailed Designs
#### 4.2.1 Design of Collimator System  
There are two functions of the collimator system. One is to form a suitable detection field of view through the collimation system and to determine the geometric factor of the probe. The other is to provide certain shielding conditions to prevent the interference of particles obliquely incident from the side of the sensor. The collimator system mainly includes three parts: the external structure, the backscatter structure, and the light-blocking layer. The external structure and backscatter structure are used to restrict the geometric factor of the instrument. The collimator system in the high-energy proton probe contains deflection magnets to deflect electrons incident into the collimator. Figure 4: Schematic diagram of the high-energy particle probe structure. Figure 3: Schematic diagram of telescope system in the high-energy particle detector. * High-energy electron collimation design  
The external structure of the collimator is the outermost support and shielding structure of the probe. It was designed as a cup shaped conical structure. To reduce the effect of obliquely incident particles from the side on the measurement results, copper shielding was added outside the probe. The opening diameter of the upper and lower ends of the high-energy electron probe was 24 mm and 5 mm, respectively, and the length was 32 mm, forming a 30\({}^{\circ}\) measurement field of view. In order to reduce the elastic scattering effect of electrons in the material, a backscatter device was added inside the high-energy electron probe with the purpose to prevent the interference of electron scattering in the measurement [29]. Figure 5 below is the schematic diagram of the collimator structure. It is known that the scattering of electrons in cutoff is more serious, especially for intermediate-energy electrons of tens to hundreds of keV. Figure 6 shows the scattering comparison between protons and electrons. From the above figure, the scattering of electrons in cutoff can be observed. When the electrons are incident into the collimator, they may not be absorbed but enter the detector through complex elastic scattering, contributing to measurement errors. Thus, in order to reduce the scattering of electrons inside the collimator, a sawtooth-shaped structure was set inside the collimator. The purpose of this structure is to increase the number of electrons scattering in the collimator, so that the electrons incident in the non-field of view are absorbed by the scattering structure, reducing the interference caused by scattering. Figure 7 shows the collimator with smooth inner walls and using collimation structure. Figure 5: Backscatter structure. Figure 6: Scattering comparison between protons and electrons (Blue: protons; Red: electrons; Green: Protons path). Figure 7: Collimator with smooth inner walls and collimator using collimation structures. In addition, the light-blocking layer design was adopted in both the high-energy electron probe and the high-energy proton probe. The purpose of the light-blocking layer was to block sunlight (because the silicon sensor is sensitive to visible light) and micrometeoroids. Its design meets the thermal and mechanical requirements [29], and its thickness has been selected to avoid an increase of the lower measurement limit of the instrument (because the light-blocking layer would reduce the energy of the incident particles). The materials of the light-blocking layer are mainly elemental films and organic composite materials. For a light-blocking layer above 10 \(\upmu\)m, an elemental material can be selected. For a layer with only about a few microns, a composite material is generally selected. The material of the light-blocking layer in the collimator of the high-energy electron probe used a 15 \(\upmu\)m aluminum film. The 15 \(\upmu\)m aluminum light-blocking layer can block protons below 1 MeV and electrons below 30 keV [29]. The electronic measurement index starts from 200 keV.