Dual Material Repeller for IHC Ion Source
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Solution Overview
Problem
Indirectly heated cathode (IHC) ion sources face issues with limited lifetime and performance degradation due to material build-up on the repeller, leading to non-uniform ion beams and contamination, caused by sputtering from electron and ion bombardment.
Innovation Solution
The repeller is designed with a disc-shaped repeller head made of a material with higher thermal conductivity than the stem, which is connected using a press fit or interference fit, allowing the repeller head to maintain a higher temperature and reduce material build-up, thereby improving ion source performance and longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the repeller is made of a single material with high thermal conductivity to maintain high temperature and reduce material build-up, then material deposition is reduced, but the structural integrity and connection reliability deteriorate due to thermal expansion mismatches and mechanical stress
Solution Approach 1:
The repeller is divided into two separate components: a repeller head made of high thermal conductivity material (tungsten) and a stem made of different material (molybdenum or stainless steel). This segmentation allows each component to be optimized for its specific function while reducing thermal stress and expansion mismatches compared to a monolithic structure.
Solution Approach 2:
The repeller uses a composite structure combining materials with different thermal and mechanical properties. The tungsten head provides high thermal conductivity for heating, while the molybdenum or stainless steel stem provides mechanical support and electrical conductivity. This composite approach resolves the contradiction between thermal performance and structural reliability.
2Loss of substance
If the repeller head temperature is increased to prevent material deposition, then material build-up is reduced, but the cathode lifetime is reduced due to increased electron bombardment damage
Solution Approach 1:
The repeller system implements local quality by concentrating high temperature in the repeller head area where material deposition occurs, while the stem and surrounding structures remain at lower temperatures. This localized heating prevents material build-up on the repeller head without subjecting the entire repeller assembly to high temperatures that would accelerate cathode degradation.
3Ease of manufacture
If a single material is used for the entire repeller structure, then manufacturing is simplified, but the thermal management performance deteriorates due to inability to optimize different regions for different functions
Solution Approach 1:
The repeller is segmented into a head and stem that can be manufactured separately using appropriate processes for each material, then assembled through press fit or interference fit. This segmentation enables optimal material selection and thermal management while maintaining manufacturing feasibility through standardized assembly procedures.
4Stability of the object's composition
If the repeller head and stem are made of the same material, then thermal expansion is uniform, but the press fit connection becomes loose at high temperatures due to thermal expansion
Solution Approach 1:
The repeller uses composite materials with different thermal expansion coefficients. The tungsten head and molybdenum or stainless steel stem have mismatched expansion properties that, when carefully selected, allow the press fit connection to maintain or improve strength at operating temperatures. The stem material is chosen to have higher thermal expansion than the tungsten head, causing the interference fit to tighten as temperature increases.
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 increased temperature of the repeller head reduces material deposition, enhancing the uniformity and purity of the ion beam and extending the life of the ion source.
Implementation Method 1
The repeller head is made from a conductive material having a higher thermal conductivity than the stem. In this way, the temperature of the repeller head is maintained at a higher temperature than would otherwise be possible.
Implementation Method 2
Differences in the coefficient of thermal expansion of the repeller head and the stem may cause the press fit to become tighter at higher temperatures.
Implementation Method 3
The filament emits thermionic electrons, which are accelerated toward and heat the cathode
Implementation Method 4
The filament emits thermionic electrons, which are accelerated toward and heat the cathode, in turn causing the cathode to emit electrons into the ion source chamber.
Implementation Method 5
The repeller may be biased so as to repel the electrons, directing them back toward the center of the ion source chamber.
Implementation Method 6
In some embodiments, a magnetic field is used to further confine the electrons within the ion source chamber.
Implementation Method 7
The electrons cause a plasma to be created.
Implementation Method 8
The cathode is subjected to bombardment from electrons on its back surface, and by positively charged ions on its front surface. This bombardment results in sputtering, which causes erosion of the cathode.
Data Source
AI summary
The IHC ion source comprises an ion source chamber having a cathode and a repeller on opposite ends. The repeller is made of two discrete parts, each comprising a different material. The repeller includes a repeller head, which may be a disc shaped component, and a stem to support the head. The repeller head is made from a conductive material having a higher thermal conductivity than the stem. In this way, the temperature of the repeller head is maintained at a higher temperature than would otherwise be possible. The higher temperature limits the build-up of material on the repeller head, which improves the performance of the IHC ion source. In certain embodiments, the repeller head and the stem are connected using a press fit. Differences in the coefficient of thermal expansion of the repeller head and the stem may cause the press fit to become tighter at higher temperatures.