Neutralization of ions is important for all electric thruster types when considering thruster efficiency and life. Hollow cathode is responsible for both creating plasma discharge and neutralization of the beam ions for Hall Effect Thruster (HET). In this study, appropriate placement of the cathode is investigated by taking into account that the decrease in cathode coupling voltage increases thruster efficiency. Regarding this, the effects of mass flow rate of the cathode and keeper current on the coupling voltage are investigated, according to available experimental results from the literature.
Tag: Plasma Applications
Note: Coaxial-heater hollow cathode
The design and tests of a LaB6 hollow cathode with a novel heater are presented. In the new design, the heater wire is completely encapsulated around the cathode tube and a coaxial return electrode, thereby eliminating hot spots on the heater wire due to the free hanging regions. Since the new heater confines the Joule heating to the region of interest, where the LaB6 emitter is placed, the heater terminals are further secured from overheating. The cathode with the presented heater design has been successfully tested and is able to deliver currents in the 0.5-15 A range.
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Thermal Analysis and Testing of Different Designs of Lanthanum Hexaboride Hollow Cathodes
Electric propulsion systems provide a higher delta-V for the same mass of propellant when compared to chemical propulsion systems due to their higher Isp levels. Many electric propulsion systems utilize cathodes as electron source. Hollow cathodes generate electron current through thermionic emission mechanism. In this study conventional hollow cathode designs are investigated numerically and experimentally. Considering the problems that are encountered with the conventional designs, a new hollow cathode design is developed, which is called coaxial hollow cathode. Operational parameters of the coaxial cathode are investigated experimentally.
Development of the New BUSTLab Hall Thruster with Internal Coaxial Hollow Cathode
HK40 Hall thruster is a low power SPT-type Hall thruster with a boron nitride (BN)
discharge channel of 40 mm in outer diameter. Based on the experience gained during the design and manufacturing of the HK40 Hall thruster, and the experiments that were conducted with this Hall thruster, an advanced larger diameter Hall thruster with an LaB6 internal cathode is developed. In the design, protection of thruster wall material is aimed by the appropriate magnetic field inside the thruster channel. Design optimization of this new Hall thruster is made by investigating the effects of different design parameters, such as magnetic circuit and discharge channel geometry. A thermal model of this thruster is developed in order to investigate the heat distribution for the thruster-cathode system.
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Design Improvements and Experimental Measurements of BURFIT-80 RF Ion Thruster
BURFIT-80, a prototype radio-frequency ion thruster, is designed, built and tested
at the Bogazici University Space Technologies Laboratory. This paper presents the design parameters and numerous design improvements of this thruster. Three different versions of the thruster, with the same discharge chamber inner diameter of 80 mm, have been built and tested. The latest version of this prototype thruster presents significant improvements of the DC electrical connections to the grids and RF electrical connections to the RF antenna. For the second version of the thruster, plume ion energy distribution measurements are conducted using an indigenously developed retarding potential analyzer, and some of the measurement results are presented.
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Summary: THE EFFECTS OF THE FERMI LEVEL ON ION INDUCED ELECTRON EMISSION FROM CHEMICALLY AND SPUTTER CLEANED SEMICONDUCTERS
In the article, low energy ion induced electron emission (IIEE) is investigated on Si and Ge semiconductors. Plasma interactions on semiconductors are recently used for etching and deposition processes. According to the previous studies, the IIEE strongly depends on the surface process but this research focuses on the sub-surfaces processes such as doping type, Fermi level of the material and cleanliness level. The studies from the literature show that the IIEE measurements are affected by the electron density in the conduction band of the semiconductor. They claim that more electrons near the vacuum potential result in larger IIEE. However, the IIEE theory predicts less dependence on electron density by assuming all the emitted electrons from the valance band. Thus, there should be no direct relation between the IIEE and doping density and type for semiconductors, on the contrary to metals.
Study of Magnetic Field Configuration Effects on Coupling between Hall Effect Thruster and Hollow Cathode
Hall effect thrusters utilize electric and magnetic fields to extract ions from a plasma discharge. In Hall effect thrusters, the ionization of the propellant gas is achieved by collisions of the neutral propellant gas atoms with the emitted electrons from a cathode, typically a hollow cathode. Besides, the cathode is responsible for the neutralization of the ion beam by emitting an equal number of electrons to prevent spacecraft charging. Proper placement of the cathode strongly affects the neutralization of ions in addition to creating well coupled discharge plasma. Studies from the literature show that the cathode coupling voltage is a function of cathode placement and thruster efficiency. Cathode coupling voltage is related to the external magnetic field lines of the thruster. This study shows that depending on the external magnetic field topology of the thruster, there could be an optimum position for the cathode considering the separatrix region.
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8th Ankara International Aerospace Conference, Ankara, Turkey, September 2015, also AIAC-2015-119.
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