## 3 Simulation Verification
### The Effect of groove Depth on the Multipactor Threshold  
In this section, the SCLPFs loaded with the PTFE sheets are employed to check how the groove depth affects the multipactor threshold. As mentioned in Figure 5, we construct groove structures on the surface of PTFE sheets, the groove number is set as 13, and the length and width of these grooves are set as 7.6 mm and 0.25 mm, respectively. Under the circumstances, the simulation is implemented to obtain the multipactor threshold of the PTFE-loaded SCLPFs as the groove depth increases from 0.02 to 0.48 mm, the simulation results are shown in Figure 9. From Figure 9, we can see that the multipactor threshold increases linearly as the groove depth increases linearly when the groove depth is smaller than 0.45 mm. However, the threshold shows a decline as the groove depth extends beyond 0.45 mm. In this case, the maximum of the multipactor threshold is about 1150 W when the groove depth is 0.45 mm.  
The simulation results of this section and the previous section indicate that the multipactor threshold will be remarkably improved as the groove number or depth increases. Moreover, the multipactor threshold may reach a saturation status when the groove number or depth increases to a certain value. The phenomenon can be explained as follows. For the SCLPFs loaded with flat dielectric sheets, there are plenty of secondary electrons emitted from the surface after one incident event during the process of multipactor. Whereas the emission of secondary electrons is changed after introducing the groove structure on the  
Figure 8: The effect of groove number on the multipactor threshold of the alumina-loaded SCLPFs.  
Figure 9: The effect of groove depth on the multipactor threshold of the PTFE-loaded SCLPFs.  
dielectric surface; the groove plays the role of shelter to increase the collision probability of the secondary electrons, and further prevents the emission of secondary electrons, which weakens the risk of multipactor from the source.  
To be specific, Figure 10 shows the circumstances of electrons impact on the central position of the bottom of a 2D groove. In this model, there is no need to focus on the interaction processes between electrons and material surfaces. Instead, we only need to consider the trajectory of electron motion to explore the specific mechanisms of microstructure impeding electron movement. In Figure 10, e#1, e#2, and e#3 are three secondary electrons produced by the incident electron, and they are probable to be captured by the sidewall and have less chance to participate in the process of multipactor discharge. In Figure 10, e#1 and e#2 are captured by the sidewall, only e#3 can escape from the groove since its emission polar angle is smaller than \(\theta\), which depends on the aspect ratio (\(h/d\)). When the groove number or the groove depth increases, the aspect ratio will increase and \(\theta\) will decrease accordingly. In this process, more electrons will impact the sidewall, and the multipactor process can be weakened. As for the reason for saturation, it can be seen that when the groove narrows linearly or the depth increases linearly, \(\theta\) will decrease and the rate of decrease gradually slows down. Although the number of electrons captured by the sidewall will also increase, the increase is extremely slow, and the suppression of multipactor tends to be saturated.