Plasma Physics at Gettysburg College

Student Research

The Goal

Our goal was to explore the plasma wave-particle interaction utilizing LIF spectroscopy, and to advance our understanding of wave-particle interactions by applying LIF spectroscopy to the study of nonlinear ion acoustic waves, ion acoustic shocks, and solitons.

We struck our first discharge during the summer of 2000 and examined it with Langmuir probes.  A Coherent model #699-21 scanning narrowband ring dye laser system was already in place.  We directed the laser beam into the double plasma device, and the collection of the LIF signal with imaging telescopes to yield a characterization of the argon plasma under diverse steady-state operating conditions.  This effort served to benchmark the device, using for reference corresponding measurements performed previously with intrusive instruments such as gridded electrostatic energy analyzers.  We would then proceed with experiments that explored excitation and propagation of linear ion acoustic waves.  We measured wave dispersion (w vs. k) using LIF methods discussed above and compared our results with predictions from linearized Vlasov models.  The linear wave-particle interaction was revealed by measurements of ion Landau damping.  This part of the plan was be executed in order to verify the applicability of this diagnostic scheme to problems of conceptual simplicity appropriate for uninitiated student assistants.

The Work

After a four year hiatus spent conducting space weather research at West Virginia University and the University of Maryland, Professor Tim Good began, in the Summer of 2000, to supervise some Gettysburg students' work with two Gettysburg College physics students to make the Pickets Charged Plasma Device (PCPD) operational. 

Since the equipment had not been used for quite some time, the first task of the summer for students Sean Lyman, '01, and Amy Kerr, '03, was to bring the device back up to operating conditions.  After initial tests of the efficiency of the vacuum pumps, it was quickly discovered that the mechanical pump needed repair, as it was only lowering the pressure of a small volume to approximately 4 Torr.  A replacement was quickly found and installed; the mechanical pump alone can now lower the pressure to approximately .05 Torr.  With the mechanical pump repaired, the oil diffusion pump's efficiency could also be tested.  Although their controllers were giving acceptable readings for the pressure, they soon encountered another problem: their ion gauge proved faulty, often turning itself off or not even lighting.  They therefore turned our attention to possible sources of leaks in the vacuum.  A replacement gauge soon proved more successful than the original gauge, yet they still continued to check the joints and connections, taking care to clean and regrease all O-rings.  They also checked for oil contamination in the piping and changed the oil in our oil diffusion pump.  by the end of the summer of 2000, Amy and Sean had succeeded in coaxing a faint purple glow from PCPD, as the first argon plasmas were ignited in the device.  Sean and Amy conquered some vacuum and power supply problems and modified the plasma filament source, while characterizing the plasma operating conditions using a Langmuir probe.    

The next cast of plasma researchers conducting a summer research campaign in 2001 included Holly Sheets, 03, and Rob Vary, 03, thanks to stipend support from the Delaware Space Grant Consortium.  Holly and Rob learned to excite ion acoustic waves in the double plasma of PCPD, and to diagnose the ion velocity distribution via laser induced fluorescence spectroscopy.  The research was aimed at gaining a greater understanding of the plasma-wave particle interaction employed in many particle acceleration and plasma heating methods, as well as in wave generation methods.

Wave-particle and field-particle interactions also play a key role in particle acceleration mechanisms believed to be operating in the auroral acceleration region of the earth's magnetosphere and more generally, in the domain of space plasmas.

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