Building custom magnetic field coils, pulsed power systems, and scientific instrumentation since 2005
Plasma Particle Flux
A Fundamental technique for measuring the properties of plasmas is the use of electrostatic probes, most notably the Langmuir probe, Mach probe, and retarding field analyzer (RFA). These probes are inserted into the plasma and thus allow local measurement of several plasma properties. The Langmuir probe measures the electron energy, temperature, and density and comes in single, double, and triple tip configurations, which have various effects on the plasma. Some of these configurations are able to measure the floating potential and/or plasma potential. A Mach probe is used to measure the ion flow velocity. Retarding field analyzers can measure the ion or electron energy and temperature in specific directions. Each electrostatic probe configuration has its advantages and disadvantages and the scientists at WSI can help you decide which probe is right for you. Two excellent references for electrostatic probes are Hutchinson's Principles of Plasma Diagnostics and Noah Hershkowitz's chapter in Plasma Diagnostics: Discharge Parameters and Chemistry. References for specific applications of each type of probe are provided in the sections below.
When requesting a quote for an electrostatic diagnostic, please consider the following:- Quantity to be measured and its expected magnitude. Electron or ion measurements? Is electron density of interest? Ion flow velocity or energy and temperature? Are floating and/or plasma potential of interest?
- Frequency response. What is the frequency (or range of frequencies) that need to be measured? What is the timescale of evolution of the measured quantitiy?
- Digitizer dynamic range. What is the peak-to-peak signal amplitude that your data acquisition system can handle?
- Vacuum environment. Is the probe intended to be used in air or vacuum? High vacuum (HV, 10-3 - 10-9 torr) or ultra-high vacuum (UHV, 10-9 - 10-12 torr)? This helps us determine the materials that can be used for your application.
- Thermal environment. Will the probe experience high heat loads (for example, behind first wall tiles) or low heat loads? Will it experience thermal cycling? Will it be used at a high or low ambient temperature (will the chamber be baked)? This information also places restrictions on the materials that can be used.
- Mounting interface. Will the probe be mounted to a vacuum flange, a custom mounting structure on the chamber wall, a reciprocating drive, or something else?
- Size constraints. Diameter of port through which the probe must be inserted, distance from the mount to the measurement location within the plasma, perturbation to the plasma, et cetera.
Langmuir Probes
- Langmuir Probes
- Single Tip
- Double Tip
- Quad Tip
- Flat
Double-tip Langmuir Probe
Available in Single, Double, Triple, or Quad tip configurations. Built for UHV environments. Probe size customizable depending on plasma parameters. Reciprocating probes available. Flat probes also available.
Gridded Ion Energy Analyzers
Retarding Field Analyzer