## 5 Discussions
[76] produced BC at 1800 W  
Figure 13: The representative images of the HPT during a testing sequence in Pulse Width Modulation (PWM) mode, operating with a forward power of 500 W (**a**) 15 ms, (**b**) 30 ms, (**c**) 45 ms, and (**d**) 60 ms after ignition initialization. The sequence features 1 sec of RF on-time followed by 0.4 s of RF off-time. using argon and a helical antenna. The direct transition from E-mode to W-mode can be attributed to the optimized RF power modulation and inhomogeneous magnetic field configuration generated by eight plate-shaped samples of neodymium iron boron (NdFeB), while featuring gold plating (Ni-Cu-Ni-Au) leads to a broad range of magnetic field values that are accessible in the near field of the antenna. This PM arrangement enables helicon waves to extend deeper into the plasma column, facilitating the transmission of electromagnetic energy, which is subsequently absorbed via wave resonance. A potential mechanism driving the W-mode operation is the resonant interaction between the fast branch helicon waves and the highly damped electrostatic TG waves. Under these conditions, the ME-ICP reactor in the HPT demonstrates a hybridized behavior (B/E), primarily due to the interaction and mixing of electromagnetic components (helicon waves) with electrostatic components (TG waves). The variations in the wavelengths of 434.8 nm and 480.6 nm in the blue core exhibit remarkable sensitivity, maybe attributed to the non-uniform magnetic field in that specific area. In the discharge process, the reflection of helicon waves by a magnetic field gradient leads to the generation of a standing wave, therefore enabling the deposition of energy. Experimental findings suggest that the existence of a non-uniform magnetic field during the discharge of helicon plasma is beneficial for the absorption of radio frequency power, thereby facilitating the development of a blue core. Figure 14: WHP mode emission spectrum of the Helicon Plasma Thruster with a forward power of 500 W and 1 sec of RF on-time followed by 0.4 s of RF off-time. Figure 15: Comparison of the Argon Plasma Spectra for ICP and Helicon modes of operation in 404–493 nm. The multi mode operation of the MEICP reactor, transitioning from E-mode to H-mode, highlights the high adaptability of this EP technology for complex maneuvers such as orbit insertion, station keeping, orbit maintenance, and attitude control. Pulsing the discharge within a comprehensive testing framework improves the ion-to-neutral influx ratio and enables rapid control of the reactor's operating modes. Regarding acceleration, Figure 13b,c demonstrate a radiant plasma plume in WCP mode, providing evidence for the generation of ionic shock waves when subjected to a pulse wave modulation of 500 W. The plume is highly concentrated and intense, characterized by the visible shock waves pulsating through it, indicating ion acceleration. The initial calculation of propulsion metrics assumes that the flow of argon ions is comparable to that of a classical sheath with a density reduction of approximately \(exp(-1/2)\sim 0.6\)[77]. Consequently, the plasma density decreases by around 40% [78] as it passes through the critical section of the HPT, defining a supersonic flow regime. With the increase in RF power, there was a notable rise in the intensity of high-energy electron-excited spectral lines within the 400-500 nm wavelength range. According to the NIST Atomic Spectra Database [72], peaks corresponding to Ar II in this region corroborate the presence of a helicon-wave (HW)-sustained discharge [76; 79; 80; 81; 82]. Additionally, a collisional-radiative model was used to simulate the intensities of the \"red lines\". Spectral lines of argon in helicon plasma are powerful tools for understanding the complex processes occurring in the plasma.