使用三探針式蘭摩爾探針測量脈衝電漿推進器之電漿特性研究

Abstract

脈衝電漿推進器(Pulsed plasma thruster, PPT)早在1960年代便成功應用在衛星上，是電力推進器的一種，是以推進劑為介質，以電弧 (Arc)放電離子化產生電漿，並在放電過程產生磁場，在電場與磁場作用下，電漿受到勞倫茲力 (Lorentz force)加速推出，產生推力。脈衝電漿推進器主要的優點為: 1) 構造簡單， 2) 不需壓力容器及管線，3) 雖然可提供之最大推力偏低，但其比衝值高於傳統化學推進器，相當適合需要節約燃料以達到長時間使用之目的，近年來多發展應用於奈米衛星上以增加其任務壽命。

本研究製作一套以鐵氟龍為燃料的脈衝電漿推進器初步實驗樣板，裝載三角形漸擴式及長方形平行式電極，搭配2 μF、20 μF及30 μF的電容，量測在環境壓力為2 ×〖10〗^(-6) mbar的真空環境中，產生之電漿特性與推力之關係比較。

結果發現在放電電極偏壓為1到1.3 kV時，產生的電子溫度約3~4 eV。在相同電容儲存能下，電容量影響放電時間即產生電漿量的不同，為影響脈衝電漿推進器推力之主要原因。三角形漸擴式電極因電場集中，瞬間產生之電漿密度較平行板式電極高，且漸擴式外型，使得產生之電漿有空間向外擴散，因此有較好的推進效能。

Pulsed plasma thruster, which is a type of the electrical propulsion, has been developed since 1960s. Pulsed plasma thruster is based on propellant as the medium. It generates a current sheet which ionizes the propellant gas and induces a magnetic field when the thruster functions. Lorentz force is the interactive effect between electric field and magnetic field which produces the thrust. The advantages of pulsed plasma thruster include: 1) simple configuration, 2) no pressure vessel and pipeline needed, and 3) higher specific impulse but much lower thrust as compared to chemical propulsion. This is suitable for saving fuel to achieve the long-distance space flight. In recent years, the application of PPT has been wide spreading to nano-satellites which increases their mission life.

In this thesis, a prototype of a pulsed plasma thruster using PTFE as the propellant has been designed and manufactured. The prototype has been operated successfully in an in-house vacuum chamber with a pressure of 2 x〖10〗^(-6) mbar. The plasma properties of the PPT was characterized under different test conditions using a Langmuir triple probe.

The results show that the PPT generates the plasma plume with an electron temperature of 3-4 eV when the electrode bias is in the range of 1-1.3 kV. Under the same stored energy in the capacitor, the larger the capacitance the larger the thrust was because of longer discharge time with a larger quantity of plasma in the plume. In addition, rail-tongue flare electrode type has better efficiency in thrust performance as compared to the parallel-plate electrode one, because not only higher electron density generated but also more space for plasma to expand.