This summer Gordon McCann and I (Avery German) are working with Dr. Good in the Plasma Research Lab. So far most of our work has been upgrading the equipment in the laboratory with the goal of using Laser Induced Fluorescence (LIF) to measure the characteristics of our plasma.
What is plasma?
When enough energy is pumped into a gas, the electrons of the gas atoms break free and we are left with a cloud of negatively charged electrons and positively charged ions. Making up 99% of the matter in the universe, plasma is extremely common in space, but not so much on earth. Examples of plasmas found on earth include lightning, fluorescent light bulbs, and neon signs.
How do you make plasma in the lab?
Here at Gettysburg College we make plasma inside of a vacuum chamber where we pump out any air and pump in a small amount of Argon gas. We then run a large amount of current through tungsten filaments within the chamber which causes the filaments to release electrons and create Argon plasma.
Progress so far
A great deal of the work done this summer has been dedicated to upgrading our equipment as well as identifying and mending any leaks in the vacuum chamber. Upgrades we’ve made include a new system of regulating the pressure inside the chamber, a method of recording plasma measurements quickly and directly to a computer, and a new laser system for preforming our LIF measurements.
What is Laser Induced Fluorescence?
In our laboratory we plan to use LIF as a plasma diagnostic tool to measure characteristics of the plasma such as temperature, flow speed, and plasma density. Older diagnostic methods include the use of metal probes inserted into the plasma but have their disadvantages. When a laser of a particular wavelength is beamed into the plasma, the light is absorbed and a light of a different wavelength is emitted. By observing the wavelength of the absorbed light, and the intensity of the emitted light, we are able to determine the characteristics of our plasma.
The end goal of our project is to use LIF to study the behavior of ion acoustic waves in our plasma. Currently we are using a Langmuir probe to make measurements and determine how our plasma behaves with different parameters (e.g. gas pressure, filament voltage). We are also beginning to launch ion acoustic waves in our plasma. Ion acoustic waves are similar to ordinary acoustic waves in air except with charged particle motion. This charged particle motion gives rise electromagnetic fields which has additional effects on the plasma.
Near future goals
As of yet we have not conducted any LIF measurements as they require multiple viewports into our plasma chamber. We plan to modify our chamber so that we may preform these LIF experiments, as well as look into LIF techniques that require only one viewport. We also have a trip planned to West Virginia University to learn from their plasma lab and preform experiments using their LIF apparatus. We expect to be able to use LIF in our study of ion acoustic waves in plasma and, using this non-intrusive optical diagnostic, to be able to learn more about the dynamical response of ions to the presence of waves.