Indirectly Heated Cathode Ion Source Voltage Dynamics
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Solution Overview
Problem
Indirectly heated cathode (IHC) ion sources face a limited cathode lifetime due to sputtering from electron and ion bombardment, which reduces the overall life of the ion source and can lead to a decrease in ion beam current over time.
Innovation Solution
The IHC ion source employs a controller to vary the voltage applied to the cathode, repeller, and electrodes over time, initially starting with positive voltages that decrease, while maintaining the target ion beam current, thereby reducing sputtering and extending the cathode's life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a constant positive voltage is applied to the electrodes to maintain ion beam current, then the ion beam current is maintained, but the cathode lifetime is reduced due to increased sputtering
Solution Approach 1:
The patent applies dynamic voltage adjustment to the electrodes, transitioning from a static constant voltage to a time-varying voltage profile. The voltage starts at a higher initial value to establish ion beam current, then gradually decreases over time to reduce sputtering damage to the cathode while maintaining adequate ion beam current throughout the cathode's operational life
Solution Approach 2:
The patent changes the voltage parameter applied to the electrodes over time. By adjusting the voltage from an initial higher value to a lower value as the cathode ages, the system optimizes both ion beam current maintenance and cathode protection against sputtering erosion
2Duration of action of stationary object
If the voltage applied to electrodes is reduced to minimize sputtering, then cathode lifetime is extended, but ion beam current decreases
Solution Approach 1:
The patent applies a higher initial voltage to the electrodes at the beginning of operation to establish the required ion beam current. This preliminary high voltage phase is followed by a gradual reduction, allowing the system to achieve both adequate ion beam current and extended cathode lifetime through the subsequent lower voltage operation
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
This approach increases the life of the IHC ion source by over 40% by minimizing sputtering through voltage adjustments, while maintaining the desired ion beam current throughout its operation.
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 chamber of the ion source
Implementation Method 2
The repeller may be biased so as to repel the electrons, directing them back toward the center of the chamber
Implementation Method 3
In some embodiments, a magnetic field is used to further confine the electrons within the chamber
Implementation Method 4
These electrodes may be positively or negatively biased so as to control the position of ions and electrons, so as to increase the ion density near the center of the chamber
Data Source
AI summary
An indirectly heated cathode (IHC) ion source having improved life is disclosed. The IHC ion source comprises a chamber having a cathode and a repeller on opposite ends of the ion source. Biased electrodes are disposed on one or more sides of the ion source. The bias voltage applied to at least one of the cathode, the repeller and the electrodes, relative to the chamber, is varied over time. In certain embodiments, the voltage applied to the electrodes may begin at an initial positive voltage. Over time, this voltage may be reduced, while still maintaining the target ion beam current. Advantageously, the life of the cathode is improved using this technique.