UCLA Physics Featured in Physics Today

The UCLA Department of Physics and Astronomy is featured in the May 2007 issue of Physics Today. While the department is often featured in this publication, the May issue is the first time that I have had anything to do with it. A photo, shown below, from the PHYS 180E course (undergraduate plasma lab) is displayed as the Back Scatter article. Back Scatter is always published as the final page of the issue and it includes one full page image related to either something from the issue or just an interesting physics item. I took the photo while serving as the TA for the class and then submitted it to Physics Today for consideration because I thought it was cool looking.

glowing filaments in a vacuum chamber

Glowing filaments in a vacuum chamber of the PHYS 180E course at UCLA.

The publication may be viewed at the website of Physics Today here, though you need to have a subscription to view it. They put together a very nice, artistic page by wrapping the caption around the right edge of the chamber’s circular cross section. While I am not allowed to repost the full page, I can display the original caption that I offered, co-written with fellow graduate student Anne White (Physics Today wrote a shorter version):

Undergraduates Discover Invisible Plasma

Eleven tungsten filaments are seen glowing white hot at one end of a cylindrical vacuum chamber (approximately 36 cm diameter and 1.2 m in length) used for the undergraduate experimental plasma course at UCLA. The filaments emit electrons that are accelerated into the chamber wall to ionize background neutral gas. There is no visual confirmation of plasma in the chamber because the intensity of light from the filaments is considerably greater than that emitted from the plasma-neutral interactions. These same atomic interactions lead to the brilliant colors of the aurora and bright neon lights, both visible plasma phenomena, the lack of which here causes students to question whether they have actually generated a plasma. The existence of plasma is confirmed through analysis of data they obtain using Langmuir probes. One such probe is shown here, extending the axial length of the chamber and allowing for measurements within 1 cm of the filaments. Typical plasma parameters include densities of 10^8 cm^-3, electron temperatures of 2 electron-Volts [eV] (while the filaments themselves are only heated to approximately one-tenth of an eV), and a background neutral gas pressure of 0.5 mTorr. Students encounter practical challenges of experimental plasma physics. These include, interpreting non-ideal Langmuir probe data, limited diagnostic access through the vacuum chamber due to the small number of ports, and plasma-wall interactions in which surface chemistry affects plasma parameters.

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