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

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 215
Author(s):  
Ugur Kokal ◽  
Nazli Turan ◽  
Murat Celik
Keyword(s):  
Electric Propulsion ◽  
Material Selection ◽  
Thermal Analyses ◽  
Surface Current ◽  
Experimental Tests ◽  
Conductive Heat ◽  
Hollow Cathodes ◽  
Cathode Design ◽  
Modes Of Failure ◽  
Current Emission

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.

Resistive MHD modes in hollow cathodes external plasma

2021 ◽  
Author(s):  
Giulia Becatti ◽  
Francesco Burgalassi ◽  
Fabrizio Paganucci ◽  
Matteo Zuin ◽  
Dan M Goebel
Keyword(s):  
Magnetic Field ◽  
Hollow Cathode ◽  
Electric Propulsion ◽  
Axial Magnetic Field ◽  
Mhd Equations ◽  
Linear Perturbation ◽  
Plasma Parameters ◽  
Hollow Cathodes ◽  
Plume Region ◽  
Helical Mode

Abstract A significant number of plasma instabilities occur in the region just outside of hollow cathodes, depending on the injected gas flow, the current level and the application of an external magnetic field. In particular, the presence of an axial magnetic field induces a helical mode, affecting all the plasma parameters and the total current transported by the plasma. To explore the onset and behavior of this helical mode, the fluctuations in the plasma parameters in the current-carrying plume outside of a hollow cathode discharge have been investigated. The hollow cathode was operated at a current of 25 A, and at variable levels of propellant flow rate and applied magnetic fields. Electromagnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probe signals provided spatial-temporal characterization of the generated waves. Time-averaged plasma parameters, such as plasma potential and ion energy distribution function, were also collected in the near-cathode plume region by means of scanning emissive probe and retarding potential analyzer. The results show that the helical mode exists in the cathode plume at sufficiently high applied magnetic field, and is characterized by the presence of a finite electromagnetic component in the axial direction, detectable at discharge currents $\geq$ 25 A. A theoretical analysis of this mode reveals that one possible explanation is consistent with the hypotheses of resistive magnetohydrodynamics, which predicts the presence of helical modes in the forms of resistive kink. The analysis has been carried out by linear perturbation of the resistive MHD equations, from which it is possible to obtain the dispersion relation of the mode and find the $k-\omega$ unstable branch associated with the instability. These findings provided the basis for more detailed investigation of resistive MHD modes and their effect in the plume of hollow cathodes developed for electric propulsion application.

Investigations into the mechanical, morphological and thermal analyses of friction stir processing of high-density polyethylene composites

2016 ◽  
Vol 232 (7) ◽  
pp. 1193-1200 ◽  
Author(s):  
Jicheng Gao ◽  
Chao Li ◽  
Yifu Shen
Keyword(s):  
Tensile Strength ◽  
Friction Stir Processing ◽  
High Density Polyethylene ◽  
Thermal Analyses ◽  
Experimental Tests ◽  
Traverse Speed ◽  
High Density ◽  
Scanning Calorimetry ◽  
Friction Stir ◽  
Polyethylene Composites

The aim of this work is to fabricate the high-density polyethylene–copper composites by submerged friction stir processing at different traverse speeds. The scanning electron microscopy is used to analyze the distribution of microstructure and particles. The experimental results indicated that the macrostructure morphology, microstructure and tensile strength vary depending on the traverse speed. Compared with the pure high-density polyethylene, Cu-filled polymer composites showed lower tensile strength and higher microhardness. The maximal values of the tensile strength and microhardness were achieved at traverse speeds of 30 and 15 mm/min, respectively. The thermal properties of Cu-filled high-density polyethylene composites were studied by differential scanning calorimetry. The crystalline content of the composites was decreased due to the addition of copper. From the experimental tests, it can be concluded that submerged fiction stir processing has a great potential for producing polymer–metal composites.

Recent progress in research and development of hollow cathodes for electric propulsion

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
Dan R. Lev ◽  
Ioannis G. Mikellides ◽  
Daniela Pedrini ◽  
Dan M. Goebel ◽  
Benjamin A. Jorns ◽  
...  
Keyword(s):  
Research And Development ◽  
Electric Propulsion ◽  
Recent Progress ◽  
Hollow Cathodes

scholarly journals Definition of the Main Features of Material Assemblies for Thermal Protective Clothing During External High-temperature Effect Modelling

Tekstilec ◽  
2021 ◽  
Vol 64 (2) ◽  
pp. 136-148
Author(s):  
Nataliia Ostapenko ◽  
◽  
Marina Kolosnichenko ◽  
Larysa Tretiakova ◽  
Tatyana Lutsker ◽  
...  
Keyword(s):  
High Temperature ◽  
Protective Clothing ◽  
Heat Insulation ◽  
Material Selection ◽  
Experimental Tests ◽  
Heat Resistant ◽  
Lack Of Information ◽  
Thermal Protective Clothing ◽  
Definition Of ◽  
Selection Of

A computational-experimental method of material selection for thermal protective clothing design is proposed in this article. The intended operating temperature of the garment lies within the range of 40−170 °С. The prereq¬uisite for the research was the lack of information regarding changes in the physical-mechanical and ergonomic characteristics of material assemblies during their use under high-temperature conditions. During the initial stage of research, there was a problem associated with the selection of the most important and the exclusion of the least significant indicators, in order to further reduce the number of experimental tests in laboratory and industrial conditions. The authors used the method of expert evaluations to solve the problems related to the selection of the most significant indicators for material assemblies. Material assemblies were formed by vary¬ing the combinations of heat-resistant, heat-insulation and lining layers of materials. Initial information for the proposed method was obtained from the experimental tests of sixteen material assemblies. According to the results of the ranking, the main parameters of material assemblies were identified as follows: the temperature range for which the use of clothing is intended, thickness, mass per unit density, rupture resistance, relative tear¬ing elongation, change in linear dimensions during mechanical loads, air permeability and change in assembly thickness during cyclic loads. It was established that the assembly that includes heat-resistant material of the Nomex comfort N.307 220 top, Nomex Serie 100 heat-insulation lining and Nomex TER 135 lining provides the necessary level of protection, reliability and ergonomics, and meets cost requirements.

scholarly journals Development of Hollow Cathodes for Space Electric Propulsion at Sitael

Aerospace ◽  
2017 ◽  
Vol 4 (2) ◽  
pp. 26 ◽  
Author(s):  
Daniela Pedrini ◽  
Tommaso Misuri ◽  
Fabrizio Paganucci ◽  
Mariano Andrenucci
Keyword(s):  
Electric Propulsion ◽  
Hollow Cathodes

Hollow Cathodes for Electric Propulsion Utilizing Scandate Cathodes

2015 ◽  
Author(s):  
Wayne L. Ohlinger ◽  
Bernard Vancil ◽  
James E. Polk ◽  
Victor Schmidt ◽  
John Lorr
Keyword(s):  
Electric Propulsion ◽  
Hollow Cathodes

Experimental Research of Corner Joints in Steel-Framed Structures under Fire Conditions

2014 ◽  
Vol 578-579 ◽  
pp. 374-377
Author(s):  
Yu Wang ◽  
Yong Jun Liu ◽  
Lin Qi
Keyword(s):  
Elevated Temperatures ◽  
Experimental Testing ◽  
Zinc Coating ◽  
Experimental Tests ◽  
Premature Failure ◽  
Steel Connections ◽  
Modes Of Failure ◽  
Endplate Connections ◽  
In Fire ◽  
Thread Stripping

The research involved experimental testing of simple steel connections and components (structural 8.8 bolts) at elevated temperatures. High temperature tests on structural bolts demonstrated two modes of failure at elevated temperatures: bolt breakage and thread stripping. In order to prevent the thread stripping in a connection,the manufacturing process of bolts and nuts has been investigated and the ‘over tapping’ of nut threads to accommodate the (zinc) coating layer for corrosion resistance has been indentified as a primary reason resulting in this premature failure between bolts and nuts. Experimental tests on endplate connections revealed the ductility of these connections to decrease at high temperatures, which might hinder the development of catenary actions in fire if plastic hinges are attempted to be formed within the connection zones. Component-based modelling and finite element simulation have been utilized for investigation of the performance of these connections.

Hollow Cathode With Low Work Function Electride Insert

2011 ◽  
Author(s):  
Lauren P. Rand ◽  
Ryne M. Waggoner ◽  
John D. Williams
Keyword(s):  
Work Function ◽  
Hollow Cathode ◽  
Electric Propulsion ◽  
Thermionic Emission ◽  
Basic Material ◽  
Successful Operation ◽  
Hollow Cathodes ◽  
Start Up ◽  
Attractive Option ◽  
Lower Temperature

Hollow cathodes are critical devices in the successful operation of electric propulsion thrusters. Cathodes featuring C12A7:electride as an ultra-low work function thermionic emitter are hypothesized to have faster start-up times and lower operating temperatures than conventional hollow cathodes. C12A7:electride is a crystalline ceramic in which electrons clathrated in sub-nanometer sized cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7:electride has a predicted work function of 0.6 eV. As a result, C12A7:electride is an attractive option for a thermionic emission material in a hollow cathode. Calculations predict equivalent levels of current emission as LaB6 or CeB6, but at much lower temperature. C12A7:electride is stable at temperatures below its re-crystallization temperature (∼1000 °C) and is not consumed during operation. C12A7:electride has been fabricated at CSU using a simplified, one-step approach that results in a more conductive material than previously reported. The material has been integrated into a novel hollow cathode design that takes advantage of its unique properties to decrease start-up time and power consumption. Our paper will discuss preliminary results obtained with several cathode configurations. In addition, results from the experimental determination of basic material properties such as conductivity and work function will be presented. Strategies to further enhance electron emission through surface modifications will also be discussed.

Open Electric Propulsion with an Application to Thermionic Orificed Hollow Cathodes

2020 ◽  
Author(s):  
Pierre-Yves Taunay ◽  
Christopher J. Wordingham ◽  
Edgar Y. Choueiri
Keyword(s):  
Electric Propulsion ◽  
Hollow Cathodes
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