Ion Source Extraction Plate Biasing for Plasma Density
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Solution Overview
Problem
Indirectly heated cathode ion sources face inefficiencies due to plasma density decrease towards the extraction aperture and whisker formation, leading to non-uniform ion beam extraction.
Innovation Solution
An electrically isolated extraction plate allows for independent voltage control, enabling enhanced plasma density through positive biasing and simultaneous ion extraction and cleaning via negative biasing, with the option of pulsed DC voltage for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional IHC ion source is used with the extraction plate electrically connected to the body, then the structure is simple, but plasma density decreases towards the extraction aperture leading to inefficient ion extraction
Solution Approach 1:
The extraction plate is electrically isolated from the arc chamber body through insulating supports, dividing the electrical system into independent zones. This allows separate voltage control of the extraction plate, enabling enhanced plasma density near the extraction aperture without increasing overall structural complexity
Solution Approach 2:
Insulating supports act as intermediaries between the extraction plate and the arc chamber body, providing mechanical support while maintaining electrical isolation. This mediator enables independent electrical control of the extraction plate, resolving the contradiction between operational efficiency and structural simplicity
2Productivity
If positive voltage is applied to the extraction plate to increase plasma density, then ion source efficiency improves, but electron losses to chamber walls increase
Solution Approach 1:
Positive voltage is applied locally to the extraction plate rather than the entire arc chamber body, creating a localized region of enhanced plasma density near the extraction aperture. This local quality change increases ion source efficiency while limiting electron losses to a specific zone, preventing widespread energy loss to chamber walls
3Reliability
If negative voltage is applied to the extraction plate to create ion-rich sheath for cleaning, then whisker formation is reduced, but ion extraction efficiency decreases
Solution Approach 1:
The extraction plate voltage is pulsed between positive and negative values, creating periodic cycles of ion extraction and cleaning. During positive voltage phases, ion extraction efficiency is maximized; during negative voltage phases, ion-rich sheath formation cleans the extraction aperture. This periodic action resolves the contradiction by alternating between the two opposing requirements
Solution Approach 2:
The extraction plate voltage transitions from static to dynamic control through pulsing. This dynamic voltage application allows the system to adapt between different operational modes (extraction and cleaning), enabling both high ion extraction rates and effective aperture cleaning without compromise
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 significantly increases plasma density near the extraction aperture, reduces electron losses, and allows for simultaneous ion extraction and cleaning, improving the ion source's efficiency and beam uniformity.
Implementation Method 1
The filament emits thermionic electrons, which are accelerated toward and heat the cathode, in turn causing the cathode to emit electrons into the arc chamber of the ion source
Implementation Method 2
The cathode and repeller may be biased so as to repel the electrons, directing them back toward the center of the arc chamber
Implementation Method 3
In some embodiments, a magnetic field is used to further confine the electrons within the arc chamber
Implementation Method 4
By applying a more negative voltage to the extraction plate, an ion rich sheath adjacent to the extraction aperture can be created
Implementation Method 5
In this mode, conditioning and cleaning of the extraction plate is achieved via ion bombardment
Data Source
AI summary
An indirectly heated cathode ion source having an electrically isolated extraction plate is disclosed. By isolating the extraction plate, a different voltage can be applied to the extraction plate than to the body of the arc chamber. By applying a more positive voltage to the extraction plate, more efficient ion source operation with higher plasma density can be achieved. In this mode the plasma potential is increased, and the electrostatic sheath reduces losses of electrons to the chamber walls. By applying a more negative voltage, an ion rich sheath adjacent to the extraction aperture can be created. In this mode, conditioning and cleaning of the extraction plate is achieved via ion bombardment. Further, in certain embodiments, the voltage applied to the extraction plate can be pulsed to allow ion extraction and cleaning to occur simultaneously.