## 1 Introduction  
Radar is the cornerstone of modern technology, allowing us to determine the spatial location of targets from great distances through the use of electromagnetic waves. As radar technology advances, so does the development of effective countermeasures, such as wave absorption technology [1, 2]. Correspondingly, plasma is drawing increasing attention as a new type of wave absorbing material [3, 4]. The plasma element is a medium that is able to displace ions and electrons. When an electromagnetic wave interacts with the plasma element, it gives energy to the particles, but only a small fraction of that energy is returned [5]. Some of the missing energy during this process may be converted into heat by scattering or resonant acceleration that occur between the electromagnetic wave and the plasma, and dissipate thereafter [6]. The possibility of being detected by radar can therefore be effectively reduced by the mechanisms such as the reflection, refraction and absorption of electromagnetic waves by the plasma elements [7]. By reducing an aircraft's radar cross-section (RCS), plasma can significantly enhance radar stealth capabilities, resulting in shorter detection distances, larger blind spots, and reduced warning times. Plasma density and temperature are key factors affecting the absorption performance of plasma elements [8]. Increasing the plasma density can facilitate the attenuation of the electromagnetic waves in plasma elements and then achieve stealth against the radar across the entire band. Increasing the plasma temperature, which results in an increased plasma collision frequency, can also help accelerate the attenuation of radar electromagnetic waves within a certain range. Therefore, the dynamic adjustment of plasma density and temperature are required in the face of different types of radar systems. Namely, the design of the plasma generator is a crucial aspect of plasma absorption technology. There are two main types of plasma generators currently available: the atmospheric generator and the low-pressure plasma generator. The former has an open structure, while the latter has a closed one. While both types have their own strengths in various applications, for electromagnetic absorption technology, the low-pressure plasma generator is preferred for the following reasons:  
1. Volume and size. Atmospheric plasma generators are typically large and made of steel, making them difficult to use on aircraft due to their weight and size. In contrast, the low-pressure generator is much simpler and lighter, using wave-transparent materials like glass to construct the cavity. 2. Energy consumption. The main discharge mode of atmospheric plasma elements is arc discharge, which requires a high current of tens of amps, resulting in high energy consumption. The low-pressure plasma generator, on the other hand, uses glow discharge as its main discharge mode, which consumes less energy due to the low gas pressure inside its cavity. 3. Plasma maintenance. The full surface coverage of a layer of plasma can achieve the best electromagnetic absorption. However, the atmospheric plasma element can easily disturb the plasma generated on a high-speed flying vehicle. Conversely, the low-pressure plasma generator has the plasma generated within a closed cavity, ensuring a long-lasting effect [9]. Given these advantages, low-pressure plasma generators show greater potential for plasma absorption technology compared to atmospheric generators. Consequently, substantial efforts have been dedicated to enhancing their plasma absorption performance. In 1956, [PERSON] filed a patent application for an \"Object camouflage method and apparatus\", using ionizing clouds to refrac or absorb incident radar waves [10]. In 1962, [PERSON] et al. conducted a study of the RCS measurements of target objects covered with plasma [11]. In 1990, [PERSON] found that plasma produced in air or in helium at atmospheric pressure is an excellent absorber of electromagnetic waves.