Two summers at Kirtland Air Force base builds plasma knowledge for PhD student

Even most non-scientists have a good understanding of how solids, liquids, and gases behave. But plasma, the fourth state of matter, holds mysteries even for scientists whose life’s work is to study it. Over the past two summers, aerospace engineering Ph.D. student Allison Timm got a crash course in generating and measuring plasma, with an emphasis on plasma diagnostic development and implementation, at the Air Force Research Laboratory in Albuquerque, New Mexico.

“I received a National Defense Science and Engineering Graduate Fellowship to design, develop, and characterize an engineering payload package for the in-space characterization of electric propulsion plasma plumes. To do that work, I needed more background and hands-on experience. I was accepted into the AFRL Scholars Program at Kirtland Air Force Base to design, develop, and test plasma diagnostics. My goal for the summer was to meaningfully contribute to an active AFRL project while learning the fundamentals of plasma diagnostics so I could implement them across a range of plasma sources,” Timm said.

Timm is one of Joshua Rovey’s doctoral students in the Department of Aerospace Engineering in The Grainger College of Engineering, University of Illinois Urbana-Champaign. During the two summers at AFRL she worked with her Kirtland mentor Remington Reid, who is a plasma physicist.

“While I was at AFRL, I worked with a direct current plasma source. DC plasma sources are made up of two metal plates which you bias while filling the gap between them with a gas. The electric field generated between the plates causes the gas to break down and form a plasma. DC plasma sources do not operate the same as electric propulsion plasma sources, but they are inherently more stable. Plasma generated by electric propulsion systems is typically transient which makes it difficult to discern if new diagnostics are behaving as they should. There are still different regions of behavior in a DC plasma, but it’s easier to verify that diagnostics are operating correctly in a DC plasma.”

Timm said she read a lot of textbooks Reid recommended to her that first year and worked on probe simulations.

“I played around with how a Langmuir probe operates, both in a single and a double probe configuration. Langmuir probes can be used to determine the electron temperature, electron density and floating potential of a plasma.”

By the end of the two summers, Timm said she feels proficient with vacuum systems. The diagnostics experience, in addition to having numerous AFRL experts close by for collaboration, put her in a great place to progress with her National Defense Science and Engineering Graduate Fellowship project.

“The AFRL scholars program works well if you can go two summers in a row. The first summer my work was a little delayed because I had to get up to speed on the project and wait for equipment to arrive, but the second summer, I was able to order the parts I needed ahead of time and hit the ground running. I was doing science by Friday of my first week.”

Timm said she enjoys the hands-on aspect of being an experimentalist, as well as the troubleshooting/problem-solving nature of working in a lab.

“I like building probes, testing them, and saying, ‘Well, that didn’t work. Let’s try something else.’ Like that first summer at AFRL, I was working with some old oscilloscopes for data collection. There was extra current hanging out in my signal and I couldn’t figure out where it was coming from. Even my mentor was puzzled by it.”

For the next summer, instead of using an oscilloscope to take the measurements, she used a data acquisition system that recorded the voltages, then read them in a LabView program.

“The first year at AFRL laid the groundwork for me to be successful the second year. That second summer, it was like a switch had flipped. I’d read so much about plasmas and diagnostics by that time, that it all just clicked.”

Timm had nothing but good things to say about working at AFRL. She was connected with a local family who had a spare room, so lodging worked out well the first year, and the family liked Timm so much, they gave her an open invitation to come again—which she did the following summer.

“I worked the 9-80 schedule. It allowed me to make good progress on my research while exploring Albuquerque and the surrounding areas on the weekends. The scholars program also gave me lots of opportunities to meet and network with people. The program hosted a career fair, professional development workshops, and lunch and learn sessions.”

At the conclusion of her second summer, Timm was awarded the 2024 Outstanding Scholar Award for the Directed Energy Directorate. She was presented this award by Colonel Jeremy A. Raley.