Global Plasma Model in DC Dual Stage Gridded Ion Thrusters

Gridded Ion Thruster (GIT) is a versatile space propulsion device that can be used for a wide range of space missions being characterized by a high trust-to-power ratio and a relatively high specific impulse. In recent years, there has been a significant increase in academic and scientific interest in interplanetary and deep space exploration that has shifted research resources toward boosting the performances of GITs. One promising concept is to separate the extraction process of the ions from their acceleration (Dual Stage). Some researches focused the attention on basic experiments to assess the functioning principle, some tried to simply model its Optical System (OS) and only few of them used a numerical approach to verify it. In this work a global plasma model for both the Direct Current (DC) ionization chamber and OS is proposed. The model combines analytical formulas, describing the plasma physics into ionization chamber, a linear optic model for OS, and a curve-fitting approach, to get performances and working parameters. As input it requires the diameter of the engine and the thrust or power. An educated guess is made by considering the validity of the thrust/diameter-total efficiency curve, obtained for conventional GIT, due to the lack of these data for Dual Stage Gridded Ion Thrusters (DSGIT). Despite this hypothesis, the results obtained by the model are in good agreement with the performances and working parameters of preliminary designed high power (25-50 kW) thrusters, available in open literature and selected for the validation, obtaining for the most differences less than 5 %. Finally the model has been applied to exploit the advantage of DS approach by designing a 1kW thruster: the results are very promising because a ten times smaller thruster than a conventional GIT, could have hundred times higher thrust and power density and an increment of the efficiency and the specific impulse by 25 %.