Hi! Welcome to the Laboratory for Basic Plasma Physics Research here at USD! Below you will find links to descriptions of the plasma state of matter (the hottest state of matter in the universe :) and to readings and resources that will help you see what's going on our lab.

I am working on one of those problems: the formation of the plasma sheath. It is a very cool problem. More on this presently!

My current research interests are these: basic plasma physics, low temperature plasma physics, the physics of sheath formation, ion dynamics in the plasma boundary layer, plasma-wall interactions, plasma diagnostics, laser-induced fluorescence, and the use of tunable diode lasers for ion dynamics diagnostics. My research work has been supported by the National Science Foundation and the US Dept. of Energy from 1997-2001, and from 2003 to the present. I worked in close collaboration Dr. Noah Hershkowitz at the University of Wisconsin-Madison, from 2001-2020. Noah died on 13 November 2020. The plasma physics community lost a giant, and I lost a long time mentor, someone who was more than a hero to me. I am working on a tribute article for Physics Today. Other tributes are already online. See for example some of the tributes that have been posted here, and here, and one published in Physics Today that I co-authored, here. I was very fortunate to have Noah as my thesis advisor (I finished at at UW-Madison, Dept. of Physics in '87, and got a tenure-track job here at USD later the same year). Immediately below is a picture of Noah and myself, not long after I took the job at USD, meeting at an APS-DPP meeting here in San Diego (if memory serves). I also do work in the physics education area (a little bit, when I can spare the time) related to the design of lower division and upper division physics laboratory experiments, and I am also interested in the exploration of relationships between Science and Faith.

As an undergrad at UCLA, I became fascinated with the plasma state of matter during a visit to the Plasma Physics Laboratory (Prof. Al Wong, then the Director). I eventually worked for Walter Gekelman, and Guy Dimonte while I was there. Well, I worked for Mel Plummer, really. One day I looked inside a vacuum chamber in which a plasma was confined. It was both luminous and transparent--imagine those qualities both gloriously true at the same time...it was just, just....awesome! I was able to see right through it, but also I could see the glow emitted from every cubic centimeter of it -- an amazing sight. That such a state of matter could one day, perhaps, become the medium in which sustained and controlled fusion reactions could occur and might be used to create enormous amounts of clean power was also very fascinating (also without a negative impact on global warming, but no one was talking about that in the late 70's) . After a Ph.D in plasma physics, and a transition to the world of the liberal arts undergraduate university, with small departments and smaller budgets (but with great opportunities to teach and to mentor very bright, curious, undergraduate students!--see below), I was amazed to find that there are some very cool, very fundamental problems in fundamental plasma physics still unsolved, after all this time (plasma physics and quantum mechanics are roughly the same age)....

Here's a peak inside one of our vacuum chambers; you can see the purple-blue fluorescence of the argon plasma....

Some recent graduates and collaborators at USD. Included here are Jake Schneider, Camron Proctor, Tim Welsh and Chris Yip, Quinn Pratt, Quinn, Eugene Wackerbarth, and Sam Nogami (this is at the Milwaukee 2017 APS-DPP meeting), and In-Sun Park, a visitor from Hanyang University in Seoul, Korea, who has visted twice now!

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Below are some pics from summer 2022; we presented together at the APS-DPP 2022 meeting in Spokane, WA. It was really fun! Shown here are Adrian Woodley (USD) and myself in front of his poster, a group pic of Ali Mohamed, Aaliyah Marshall (between Adrian & me), who visited us from Morgan State University. Also in the picture is Grace Farrell from Morgan State who came to the conference as well. She did research last summer with Dr. Yucheng Lan at Morgan State; Dr. Lan and I are the creators of the USD-Morgan State collaboration. Below that, Ali Mohamed (wearing a red shirt) is standing next to a really great plasma physicist, Tommie Steinberger who is at West Virginia University. The last picture is Quinn and Adrian. Quinn is just about done with his PhD thesis in Plasma Physics at UCLA, and Adrian is now finished at USD with his multiple degrees (Physics & Mech. Engineering).... Anyway, we were very fortunate last summer to have Ali and Aaliyah Marshal visit us from Morgan State University. It was a great summer and a fun conference.

• Really nice collection of short introductory videos about plasma physics and applications, hosted at Michigan Institute for Plasma Science (MIPSE), one of the great plasma science labs in the US. Check out the Plasma in our Lives section.
• Check out UCLA's Plasma Science and Tech Institute! The youtube video at the bottom is really great too! I worked for Walter as an undergrad at UCLA! Troy Carter is an world wide acknowledged leader of experimental research in plasma physics (as is Walter!)... See particularly the short videos by Mark Kushner (in 'the fundamentals' section, and then check out the videos of Wensheng Huang, Ute Ebert, Philip Bucksbaum, and Troy Carter. Go to the Propulsion section and see the one by Rich Wirz too. Then have fun looking around.
• A short course on plasma physics (2020), Princeton Plasma Physics Laboratory; of particular interest is the introduction to plasma physics, and the experimental methods lectures; for summer 2020 research students: Please register to view live stream lectures, using the link below
• Plasma is the 1st state of matter in the Universe
• Coalition for Plasma Science, check out the links...
• The International Thermonuclear Experimental Reactor (ITER); lots of cool things if you drill down
• The US ITER website
• A Fusion startup in partnership with the Japanese national fusion effort has achieved proton-boron Fusion in the LHD--Check it out!
• So, what is plasma? Check out the links herein...
• Cool intro to the basics of vacuum systems.
• 80th anniversary of the creation of the field of plasma physics [paper]
• introduction to gas discharges [paper]
• Ion Acoustic Waves [paper]
• Langmuir probes [paper]

Selected research journal articles on Sheath Formation (mostly) in Low Temperature Plasma (not very well kept up)

• Bohm's Criterion Theory and Experiment...click on some of the papers! Look at this first....
• Langmuir probes begin to fail in presheaths!
• Toward a first test of Bohm's Criterion in 3 ion species plasmas
• Invited publication of paper for laser-aided plasma diagnostics
• the first direct experimental test of an new theory of sheath formation in general (multiple-ion species) plasmas. The kinetic theory of Dr. Scott Baalrud, and our work too, has attracted both interest and controversy!
• How to use diode lasers as an LIF diagnostic for plasma ion motion (Xe+)
• the first direct test of the Bohm Criterion for a two-ion species plasma (Ar+, Xe+), both ions diagnosed via LIF, and
• An introduction to the problem of sheath formation, and the Bohm Criterion
• Bohm's criterion and sheath formation for two-ion species plasmas--this result was a surprise to the plasma physics community and began a new research journey for me. This work was done while I was on sabbatical, visiting Noah Hershkowitz in 2001. A number of papers followed, for example...
• How to use diode lasers as a diagnostic (via laser-induced fluorescence, LIF) for plasma ion motion (Ar+)

Selected conference papers and posters (also not very well kept up...check out the CV below for up2date list)

• First laser-induced fluorescence measurements of argon and xenon ion velocities near the sheath boundary in 3 ion species plasmas, Invited talk, 69th Gaseous Electronics Conference, GEC 2016, (an APS conference, triannually overseas) Ruhr-Universität Bochum, Germany 11 October 2016
• First laser-induced fluorescence measurements of argon and xenon ion velocities near the sheath boundary in 3 ion species plasmas, Invited talk, 18th International Conference on Plasma Physics (an IUPAP conference) Kaohsiung, Taiwan 29 June 2016
• Measurements of the ion drift velocities in the presheaths of plasmas with multiple ion species, Invited talk, 16th Annual Laser-Aided Plasma Diagnostics, Madison WI, 2013
• LIF studies of Discharge Plasma Sheaths, Invited talk, 45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics, June 2–6, 2014; Madison, Wisconsin
• On the plasma-sheath transition in low temperature plasmas: on the existence of a collisionally modified Bohm criterion (CMBC) "
• Experimental Studies of Kr+ with Laser-Induced Fluorescence, G.D. Severn, T. Welsh, and Noah Hershkowitz, Poster presented at the 65th Annual Gaseous Electronics Conference, 21-26 October 2012, Austin, TX
• What’s missing from the traditional explanation of NMR experiments? G.D. Severn, J.P. Bolender (Professor of Chemistry, USD), 2012 ALPha Conference on Laboratory Instruction Beyond the First Year of College, University of Pennsylvania and Drexel University, Wednesday, July 25 - Friday, July 27, 2012
• Will a magnet fall freely in a superconducting tube? G.D. Severn, T. Welsh, 2012 ALPha Conference on Laboratory Instruction Beyond the First Year of College, University of Pennsylvania and Drexel University, Wednesday, July 25 - Friday, July 27, 2012
• How might quantum physics inform our faith?, a talk given at All Soul's Episcopal Church, Point Loma, CA, 22 Nov. 2015 for their ongoing series on religion and science

• COVID-19 SAFETY POLICIES FOR THIS BUILDING (SCST)
• GENERAL SAFETY POLICIES FOR THIS BUILDING (SCST)
• General safety guidelines--however, the actual lab safety training must be in person....
• Research student safety training form (required for getting key access to the lab)
• LASER HAZARDS AND SAFETY PROTOCOLS (SCST)

How to build a Langmuir Probe

How to initiate a plasma discharge in the PaX device

Notes on LIF

CV 2020