Langmuir probe

A Langmuir probe, named after Nobel Prize winning physicist Irving Langmuir, is used to determine the ionization energy and electron temperature of a plasma. It works by inserting two wires into the plasma that are insulated on their sides from each other and the plasma. This is done so that only the tips of the wires are exposed to the plasma. The wires are typically made of tungsten which are several thousandths of an inch thick.

You then sweep a DC Voltage across the wires, typically from -100 Volts to +100 Volts and measure the current that flows through the plasma. This current will be on the order of milliamps in most cases. This allows you to determine a curve called the IV curve. I stands for current and V stands for Voltage. This curve is graphed on a conventional x/y graph of milliamps as a function of Voltage.

Mathematical analysis of this curve using calculus and physics allows the user to calculate Plasma Potential (Vp), Floating Potential (Vf), Electron Density (ne), Ion Density (ni), Electron Temperature (Te) and the Electron Energy Distribution Function (EEDF) or f(e).

A langmuir probe can be purchased off the shelf for on the order of 15,000 U.S. Dollars, or they can be built by an experienced researcher and/or technician. Beware of coupling when working at frequencies under 100 MHz. Use blocking filters. Ground everything!

WARNING: HIGH VOLTAGE CAN AND DOES KILL EVERY DAY. YOU MAY BE NEXT.