What does LP mean in UNCLASSIFIED

A Langmuir probe is a diagnostic tool used to measure the plasma parameters in gas discharges and plasmas. It consists of a metallic electrode inserted into the plasma, which is biased to a range of voltages relative to the plasma potential. By measuring the current collected by the probe, information about the electron temperature, density, and other plasma parameters can be obtained.

There are various types of Langmuir probes, each designed for specific applications:

• Single Langmuir probe: A basic probe that measures the current-voltage characteristics of the plasma.
• Cylindrical Langmuir probe: A probe with a cylindrical shape, which is commonly used in low-pressure plasmas.
• Spherical Langmuir probe: A probe with a spherical shape, which is suitable for high-pressure plasmas.
• Double Langmuir probe: A probe consisting of two closely spaced electrodes, which provides information about the electron temperature.

When a Langmuir probe is inserted into a plasma, it disturbs the local plasma potential and creates a sheath around the probe. By sweeping the probe voltage from negative to positive values, different regions of the probe's current-voltage characteristic curve can be observed:

• Ion saturation region: At negative voltages, the probe collects positive ions from the plasma.
• Electron saturation region: At positive voltages, the probe collects electrons from the plasma.
• Transition region: Between the ion and electron saturation regions, the probe current is influenced by both ions and electrons.

Langmuir probe measurements can provide valuable information about plasma parameters, including:

• Electron temperature: Estimated from the slope of the electron saturation region in the probe's current-voltage characteristic.
• Electron density: Calculated from the saturation electron current and the probe's effective area.
• Ion density: Determined by subtracting the electron density from the total plasma density, which can be estimated using other diagnostic techniques.
• Plasma potential: Measured as the voltage at which the probe current is zero.
• Sheath thickness: Inferred from the transition region of the probe's current-voltage characteristic.

Langmuir probe measurements have certain limitations:

• Perturbation of the plasma: The probe's presence can disturb the local plasma conditions, potentially affecting the accuracy of measurements.
• Sensitivity to magnetic fields: Magnetic fields can influence the trajectories of charged particles in the plasma, affecting the probe's current-voltage characteristics.
• Assumptions about plasma properties: Langmuir probe analysis relies on certain assumptions about the plasma, such as Maxwellian electron energy distribution and negligible ion current in the electron saturation region.