Heaterless Hollow Cathode Ignition With Dielectric Barrier Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional hollow cathode systems face challenges with high current operation due to thermal fatigue, non-uniform erosion, and increased costs associated with ohmic heaters, particularly when using lanthanum hexaboride emitters, which require higher temperatures and suffer from reliability issues and high power losses.
Innovation Solution
A heaterless hollow cathode apparatus is designed with a tubular dielectric barrier and electrical insulation to direct ignition discharge to the emitter, utilizing a current control device for stable and uniform heating, eliminating the need for an ohmic heater and reducing thermal shock, while maintaining efficient plasma formation and emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If ohmic heater is used to raise emitter temperature, then thermionic emission is enabled, but thermal fatigue and reliability issues occur due to thermal cycling
Solution Approach 1:
The patent removes the ohmic heater component entirely from the cathode assembly. Instead of using a separate heater to raise the emitter temperature, the system relies on direct resistive heating of the emitter through controlled current passage during the startup phase, eliminating the thermal cycling-induced fatigue and reliability issues associated with dedicated heater elements.
Solution Approach 2:
The emitter serves dual functions: it is both the electron source and its own heating element. By passing current directly through the emitter material during startup, the system enables self-heating without requiring external heater components, thereby eliminating thermal fatigue from separate heater-cathode interfaces and reducing overall system complexity.
2Productivity
If lanthanum hexaboride emitter is used for high current operation, then emission density and lifetime are improved, but ignition system complexity increases due to higher temperature requirements
Solution Approach 1:
The patent eliminates the complex multi-stage ignition system typically required for LaB6 cathodes by removing the ohmic heater, pre-heater, and associated control circuitry. The simplified system uses direct current passage through the emitter itself for heating, reducing ignition system complexity while maintaining high current emission capability.
Solution Approach 2:
The patent changes the heating mechanism from thermal conduction through a heater element to direct Joule heating through the emitter material itself. This parameter change in the heating method allows LaB6 to reach its operating temperature more directly and efficiently, reducing the complexity of the ignition system while maintaining the high emission current characteristics of LaB6.
3Device complexity
If conventional cathode design is used, then structure is simple, but erosion is non-uniform and operational lifetime is reduced
Solution Approach 1:
The patent introduces a radially extended emitter geometry that creates different local heating and emission characteristics across the emitter surface. This local quality variation ensures more uniform current distribution and ion bombardment across the emitter face, preventing localized erosion hotspots and extending operational lifetime while maintaining structural simplicity.
4Device complexity
If ohmic heater is removed for heaterless operation, then system cost and complexity are reduced, but controlled and uniform heating becomes more difficult
Solution Approach 1:
The radially extended emitter geometry creates favorable local electrical and thermal conditions that promote uniform current distribution across the emitter surface during startup. This geometric modification ensures that even without a dedicated heater, the emitter heats uniformly through self-heating, maintaining heating uniformity while reducing system complexity.
Solution Approach 2:
The patent changes the heating mechanism from external thermal conduction to internal Joule heating, and simultaneously modifies the emitter geometry to optimize current distribution. This dual parameter change ensures that the simplified heaterless system achieves uniform heating through the inherent electrical and geometric properties of the emitter itself.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables high current operation with reduced erosion and cost, achieving efficient and reliable heaterless ignition at nominal propellant flow rates and lower ignition voltages, extending operational lifetimes and minimizing thermal losses.
Implementation Method 1
The tubular emitter is composed of a material for emitting electrons into the input gas to form a plasma in the portion of the central hollow cavity when an electrical potential, above a particular potential threshold, is applied to the material of the tubular emitter
Implementation Method 2
A heaterless hollow cathode (HHC) in which the emitter heating is driven by a discharge to the emitter allows for significantly higher reliability by completely removing the heater component
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A hollow cathode apparatus includes an outer tubular dielectric barrier circumferentially surrounding an outer tubular surface of the cathode tube, the outer tubular dielectric barrier being composed of a barrier material which is electrically non-conductive. Also disclosed is a system comprising the hollow cathode apparatus, an anode which is spaced from the output end of the tubular cathode, and electrical circuitry connected between the cathode tube and the anode for connection to a source of electrical power for providing an electrical potential between the cathode and anode to cause an electric current to pass from the emitter into the input gas to form a plasma which is then output through the output end of the cathode tube to form a plasma plume. The electrical circuitry comprises: a first power supply for connecting the cathode and the cathode electrode to a first source of DC power in an ignition power mode, wherein the first power supply comprises a current control device which is adapted to control the current between the cathode and the cathode electrode, wherein the current control device is arranged to function as an anti-surge current stabiliser; and a second power supply for connecting the anode and the cathode to a second source of DC power in a steady state power mode.