Shorted Turn Mitigates Ion Current Asymmetry
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Solution Overview
Problem
Inductively coupled radio-frequency ion and plasma sources face challenges in achieving uniformity of ion current density in their beams due to the terminations of the multiple-turn inductor, which complicates their use in various applications requiring reproducibility and symmetry.
Innovation Solution
A modified radio-frequency inductor design with a shorted turn at the end closest to the ion-optics grids, which mitigates radial and azimuthal variations in ion current density without requiring additional magnetic fields or complex discharge-chamber shapes, and uses a single radio-frequency power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multiple-turn inductor is used to generate ions in an inductively coupled radio-frequency source, then ion generation efficiency is improved, but asymmetry in ion current density profiles occurs due to inductor terminations
Solution Approach 1:
The patent applies asymmetry by introducing a compensating structure with deliberate asymmetric geometry (a protrusion extending toward the inductor termination) to counterbalance the inherent asymmetry caused by the inductor terminations. This asymmetric compensating structure creates a symmetric magnetic field distribution that eliminates the azimuthal variations in ion current density while preserving the high ion generation efficiency of the multiple-turn inductor.
2Manufacturing precision
If additional magnetic fields or complex discharge-chamber shapes are used to correct ion current density variations, then uniformity is improved, but device complexity increases
Solution Approach 1:
The patent merges the compensating structure with the existing discharge chamber geometry, integrating the asymmetric protrusion directly into the chamber wall. This consolidation eliminates the need for separate complex magnetic field generation systems or elaborate discharge chamber designs, achieving uniform ion current density while maintaining relatively simple device architecture.
3Ease of manufacture
If inductor terminations are present in an inductively coupled radio-frequency source, then the inductor can be fabricated with a finite number of turns, but radial and azimuthal variations in ion current density occur
Solution Approach 1:
The patent extracts the harmful effect of inductor terminations by introducing a compensating structure that specifically targets and neutralizes the asymmetric magnetic field regions near the inductor ends. This allows the inductor to maintain its practical finite-turn construction while the compensating structure removes the detrimental termination effects, preserving both ease of manufacture and ion current density uniformity.
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 modified inductor design significantly reduces asymmetry in ion current density profiles, achieving improved uniformity and symmetry in the beam, allowing for more precise control and efficient operation of ion and plasma sources.
Implementation Method 1
a gradient in magnetic field can interact with electrons to generate an electric field in a plasma, and the electric field will accelerate ions
Implementation Method 2
the interaction of an electron current with a magnetic field, which establishes an electric field in a quasi-neutral plasma
Implementation Method 3
the plasma potential and the density are related by the Boltzmann relation, ne=ne,oexp(Vp/Te), where ne,o is the reference plasma density where the plasma potential is defined as zero, Vp is the plasma potential at a density ne, and Te is the electron temperature in electron-volts
Data Source
AI summary
In accordance with one embodiment of the present invention, the dielectric discharge chamber of a generally axially symmetric ion source has a hollow cylindrical shape. One end of the discharge chamber is closed with a dielectric wall. The working gas is introduced through an aperture in the center of this wall. The ion-optics grids are at the other end of the discharge chamber, which is left open. The inductor is a helical coil of copper conductor that surrounds the cylindrical portion of the dielectric discharge chamber. The modification that produces uniformity about the axis of symmetry is a shorted turn of the helical-coil inductor at the end of the inductor closest to the ion-optics grids.