Plasma Torch Baffle Suppresses Vortex Shedding
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Solution Overview
Problem
Plasma-based spectrometry instruments face issues with ion current noise and ambient gas entrainment due to annular vortex shedding, which affect signal precision and introduce unwanted species into the plasma, leading to interference in elemental analysis.
Innovation Solution
A plasma source configuration with a baffle positioned between the torch exit and the chamber wall, effectively suppressing annular vortex shedding by maintaining a specific axial distance and aperture size, thereby reducing noise and ambient gas entrainment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If plasma is discharged into chamber without baffle, then ambient gas entrainment occurs causing ion current noise, but adding baffle increases device complexity
Solution Approach 1:
A baffle is introduced as an intermediary component between the plasma torch exit and the chamber wall. The baffle includes an aperture that allows plasma to pass through while blocking ambient gas from being drawn into the plasma stream, thereby reducing ion current noise without completely obstructing the plasma flow path.
Solution Approach 2:
The plasma discharge path is segmented into two zones: an upstream region where plasma is generated and discharged, and a downstream region near the chamber wall. The baffle creates a physical separation that prevents ambient gas from the downstream region from mixing with the plasma in the upstream region, while still allowing controlled interaction through the aperture.
2Object-affected harmful factors
If baffle aperture is small, then ambient gas entrainment is reduced, but plasma flow is restricted affecting analysis efficiency
Solution Approach 1:
The baffle aperture dimensions are optimized to specific parameter ranges that balance two competing requirements: the aperture is small enough to block ambient gas entrainment but large enough to maintain adequate plasma flow. The aperture size is selected based on experimental optimization of plasma stability and reduction of ion current noise while preserving analysis throughput.
3Object-affected harmful factors
If baffle is positioned close to chamber wall, then ambient gas blockage is improved, but plasma stability deteriorates due to excessive confinement
Solution Approach 1:
Instead of positioning the baffle directly against the chamber wall (zero-dimensional contact), the baffle is positioned at a specific axial distance from the wall, creating a gap that allows plasma to interact with the chamber environment in a controlled manner. This axial positioning in another dimension enables the baffle to block ambient gas while avoiding excessive confinement that would destabilize the plasma.
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 detector noise and ambient gas entrainment, enhancing the precision of elemental analysis by eliminating audio frequency tones and minimizing the presence of undesirable species in the plasma, thus improving instrument performance and accuracy.
Implementation Method 1
The phenomenon has been postulated to be caused by a hydrodynamic effect occurring at the plasma torch exit (the end of the outer tube) where the hot plasma exits into the cool ambient gas (e.g., air). This effect is commonly known as annular vortex shedding, which has been postulated to be caused by the Kelvin-Hemholtz instability.
Implementation Method 2
This effect is commonly known as annular vortex shedding, which has been postulated to be caused by the Kelvin-Hemholtz instability.
Implementation Method 3
The instrument may be, for example, a spectrometer that includes a plasma-generating device (plasma source)... The plasma source often is configured as a flow-through torch having two or more concentric tubes. Typically, a plasma-forming gas such as argon or nitrogen flows through an outer tube and is energized into a plasma by an appropriate energy source
Implementation Method 4
In the plasma, unbound electrons repeatedly collide with the sample atoms or ions. As a result of this process, the atoms or ions emit electromagnetic radiation (light) at wavelengths characteristic of their elemental identities.
Implementation Method 5
The plasma is typically inductively coupled plasma (ICP) or microwave induced plasma (MIP).
Implementation Method 6
The plasma is typically inductively coupled plasma (ICP) or microwave induced plasma (MIP).
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
In a plasma source (200) configured for producing sample atoms for analysis, such as by optical emission spectrometry or mass spectrometry, a plasma torch (204) includes a torch exit (216) in a chamber (212). A baffle (276) is positioned between the torch exit (216) and an opposing boundary. The baffle (276) may be positioned and configured to suppress or eliminate vortex shedding in the chamber (212).