Modeling of LaB6 hollow cathode performance and lifetime

Pedrini, Daniela; Albertoni, Riccardo; Paganucci, Fabrizio; Andrenucci, Mariano

doi:10.1016/j.actaastro.2014.10.033

Cited by 22 publications

(9 citation statements)

References 14 publications

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“…The cathode lifetime is estimated on the basis of an evaporation model at the computed emitter surface temperature, where the lifetime is described as the time to halve the emitter initial mass. Other life-limiting mechanisms such as keeper or orifice plate erosion, or heater life, are not considered [11].…”

Section: Cathode Designmentioning

confidence: 99%

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

et al. 2017

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Hollow cathodes are electron sources used for the gas ionization and the beam neutralization in both ion and Hall effect thrusters (HETs). A reduction of power and propellant consumption from the cathode is particularly needed in small satellite applications, where power and mass budgets are inherently limited. Concurrently, the interest in high-power HETs is increasingly fostered for a number of space applications, including final positioning and station-keeping of Geostationary Earth Orbit (GEO) satellites, spacecraft transfers from Low Earth Orbit (LEO) to GEO, and deep-space exploration missions. As such, several hollow cathodes have been developed and tested at Sitael, each conceived for a specific power class of thrusters. A numerical model was used during the cathode design to define the geometry, in accordance with the thruster unit specifications in terms of discharge current, mass flow rate, and lifetime. Lanthanum hexaboride (LaB6) hollow cathodes were successfully developed for HETs with discharge power ranging from 100 W to 20 kW. Experimental campaigns were carried out in both stand-alone and coupled configurations, to verify the operation of the cathodes and validate the numerical model. The comparison between experimental and theoretical results are presented, offering a sound framework to drive the design of future hollow cathodes.

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Section: Cathode Designmentioning

confidence: 99%

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

et al. 2017

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“…As such, the maintenance of the emitter operative temperature requires higher input power from the emission region, obtained with a higher voltage drop in the emitter sheath, in turn increasing the total discharge voltage. The cathode model described in [34] corroborates this explanation; however, one of the main assumption of the model is the perfect contact conditions among surfaces (thermal gluing), an ideal situation from which experiments deviate by an amount difficult to be quantified. Further analyses will be performed, including the evaluation of the possible presence of ion acoustic turbulence at the keeper exit, which may be the cause of the increase in the discharge voltage as well [18,49].…”

Section: Hollow Cathodes Performancementioning

confidence: 69%

“…The main functional dimensions of the cathode derive from a theoretical model developed at SITAEL [34] to describe the operation of orificed hollow cathodes. The model results were analyzed to select the emitter inner and outer diameters, the emitter length, and the orifice diameter and length.…”

Section: Cathodes Descriptionmentioning

confidence: 99%

Triple Langmuir Probes Measurements of LaB6 Hollow Cathodes Plume

et al. 2019

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Lanthanum hexaboride hollow cathodes represent a viable option for high power Hall effect thruster applications, under development for the next generation of manned and robotic interplanetary missions. In this scenario, SITAEL and the University of Pisa are actively developing high current hollow cathodes capable of providing discharge current in the range 10-100 A to be coupled with high power Hall effect thrusters. The cathode design is based on an in-house theoretical model of the internal sections of the cathode, recently integrated with a simplified model of the cathode plume. Despite the application of hollow cathodes on flight and laboratory model Hall effect thrusters, many questions remain unsolved. In particular, issues related to onset of instabilities, due to plume mode or ion acoustic turbulence, are still unclear, while it is known that they can affect the overall performance of the cathode and thruster unit. This paper focuses on the experimental investigation of the cathode plume by means of measurements of the main plasma parameters, at different operating conditions and for different cathode geometry. Two cathodes were investigated, namely HC20 and HC60, designed to be coupled with SITAEL's HT5k and HT20k (5 kW-and 20 kW-class) Hall effect thrusters. The cathodes were mounted in stand-alone configuration with an auxiliary cylindrical anode. The experimental campaign was performed using triple Langmuir probes as plasma diagnostic system. The probes were mounted on scanning mechanisms to measure the plume parameters at various radial and axial distances from the keeper exit. General trends of electron temperature, plasma potential and plasma density are reported in terms of discharge current, mass flow rate and cathode orifice geometry. The results highlight that the cathode plate orifice selection affects the plume mode onset, giving the possibility to extend the stable mode of cathode operation in the current range required by the thruster.

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“…Higher temperatures, about 1500 • C, are needed for LaB 6 inserts [13,14]. However, LaB 6 emitters are much less sensitive to impurities in propellant gas and do not need special conditioning procedures, and have a longer lifetime [6,11,15,16]. High temperature at the emitter material is achieved with the use of a heater element.…”

Section: Introductionmentioning

confidence: 99%

Thermal Analysis and Testing of Different Designs of LaB6 Hollow Cathodes to Be Used in Electric Propulsion Applications

2021

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LaB6 emitters are commonly used in hollow cathodes that are utilized in electric space propulsion systems. In order to obtain necessary surface current emission densities of 1–10 A/cm2 for cathode operations, LaB6 emitters require temperatures above 1500 °C. Hence, the design for LaB6 cathodes presents thermal and mechanical challenges. In this paper, several design iterations for LaB6 hollow cathodes are presented and thermal analyses are conducted for each design. Temperature and heat flux distributions that are obtained from thermal analyses are investigated. The designs are evaluated according to the required heat input to the emitter, and the radiative and conductive heat loss mechanisms. In addition to the thermal analyses, experimental tests are conducted for different cathode designs and, based on these tests, various modes of failure are determined. Revising the cathode design and the material selection iteratively to eliminate the encountered failure mechanisms, a novel cathode design is achieved. Experimental tests of this novel cathode are conducted and current-voltage characteristics are presented for different mass flow rates and for discharge currents between 0.5 and 12 A. Tests and analysis results show that the selection of materials and design are crucial for a sturdy and long lifetime cathode.

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Modeling of LaB6 hollow cathode performance and lifetime

Cited by 22 publications

References 14 publications

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

Triple Langmuir Probes Measurements of LaB6 Hollow Cathodes Plume

Thermal Analysis and Testing of Different Designs of LaB6 Hollow Cathodes to Be Used in Electric Propulsion Applications

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