RF Cyclotron Ion Source With Coaxial Cavity for Low Erosion
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Solution Overview
Problem
Penning ion sources used in cyclotrons suffer from cathode erosion due to high-energy electrons, leading to frequent replacements and reduced ion current, especially when producing H- ions, as they contribute to the destruction of H- ions.
Innovation Solution
A low-erosion radio frequency ion source with a coaxial resonant cavity and conductive protuberance, using radio-frequency energy to generate plasma without cathode erosion, allowing for the use of less expensive materials like copper and reducing high-energy electron generation, thereby increasing H- ion production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Penning ion sources are used in cyclotrons, then ion production is achieved, but cathode erosion occurs due to high-energy electrons leading to frequent replacements and reduced ion current
Solution Approach 1:
The patent replaces the DC discharge mechanism with a radio-frequency (RF) driven plasma generation system. The RF electromagnetic field directly ionizes the gas to produce plasma without requiring accelerated electrons from a cathode, thereby eliminating the mechanical erosion process while maintaining ion production capability.
Solution Approach 2:
The patent changes the operating parameters from DC discharge conditions to RF-driven plasma conditions. By using RF frequencies (typically 13.56 MHz) to drive the plasma, the electron acceleration mechanism changes, preventing the high-energy electron bombardment that causes cathode sputtering and erosion in traditional Penning sources.
2Productivity
If DC discharge is used to generate plasma, then ionisation occurs, but sputtering and erosion on cathodes limit the life of the cathode
Solution Approach 1:
The patent substitutes the DC discharge system with an RF-driven plasma system. The RF electromagnetic field provides continuous ionization without the need for cathode-based electron emission, thereby maintaining ion production productivity while eliminating the erosive mechanism that limits cathode lifespan.
Solution Approach 2:
The patent introduces RF electromagnetic waves as an intermediary energy transfer mechanism. Instead of direct electron acceleration from cathode to anode (which causes sputtering), the RF field acts as a mediator to ionize the gas and sustain plasma, producing ions without the harmful cathode erosion process.
3Power
If high potential difference is applied to accelerate electrons, then ionisation efficiency increases, but material sputtering increases and cathode life decreases
Solution Approach 1:
The patent changes the energy delivery parameter from high DC voltage to RF electromagnetic field strength. The RF field provides sufficient energy for ionization through oscillating electric fields that resonate with electron motion, achieving high ionization efficiency without the continuous high-potential difference that drives sputtering processes.
Solution Approach 2:
The patent replaces the electron acceleration mechanism (high potential difference driving electrons from cathode) with direct RF field ionization. This substitution maintains power efficiency for ion production while eliminating the material sputtering that occurs when high-energy electrons bombard the cathode surface.
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 reduces maintenance and interruptions, extends the lifespan of ion source components, and enhances H- ion production by minimizing energetic collisions, allowing for increased ion current and efficient operation without hot cathodes.
Implementation Method 1
a power supply inlet (21) through which radio frequency energy is injected into the cavity (13)
Implementation Method 2
The conductive protuberance (22) is opposite the plasma outlet hole (17)... allowing for the use of less expensive materials like copper and reducing high-energy electron generation
Implementation Method 3
Radio-frequency discharge: they are an evolution of DC sources because they use an alternating electric field to accelerate the electrons instead of a continuous one
Data Source
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AI summary
The invention relates to a low-erosion radio frequency ion source, comprising: - A hollow body (11) with conductive interior walls that define a cylindrical cavity (13), with a gas supply inlet (14) for plasma-forming gases and a power supply inlet (21) for injecting radio frequency energy into the cavity (13). - An expansion chamber (16) connected to the cavity (13) by means of a plasma outlet hole (17). - An ion-extraction aperture (18) in contact with the expansion chamber (16). - A coaxial conductor (15) disposed in the cavity (13), parallel to the longitudinal axis thereof, one or both ends of the coaxial conductor (15) being in contact with a circular interior wall of the body (11), forming a coaxial resonant cavity; the coaxial conductor (15) having a conductive protuberance (22) opposite the plasma outlet hole (17) and which extends radially into the cavity (13). It substantially reduces the erosion of the conductive materials.