11 Plasma Physics

The plasma state of matter seems exotic and yet a vast amount of matter in the universe is in this state. So how do we bring the conditions and dynamics of plasmas readily into examination? Fortunately, there are several applications near at hand, although one type that has been commonlyplace - the low pressure discharge driving fluorescent and neon lamps - is receding as LED lighting has become a major option for everyday use. How do we define the conditions of a plasma in such discharges and reconcile the notion that high temperatures are needed to ionize gases with the fact that this particular implementations are cool to the touch? What probes can we use to interrogate the actual charged particle populations and energy distributions? What drives and sustains intense and truly hot plasmas of arcs that we observe as lightning and which are harnessed for use in welding, cutting, and intense lighting? How in fact is light produced by these plasmas and what uses can such methods of light production have? How do plasmas, both low pressure and high pressure, interact with solid surfaces and what uses do these interactions have for modifying materials? What happens when we mix solid particulates with plasmas to make so-called "dusty plasmas"? What is the nature of very-low pressure plasmas existing in space, both in the earth's ionosphere and in deep reaches of interstellar space? Given that plasmas have freely mobile electric charge, it is no surprise that many modes of internal dynamics might exist. What wavelike motions occur and how can we couple electromagnetic waves to these modes? We have high hopes for harnessing the energy driving the sun through controlled fusion: what are the key issues involved in sustaining plasmas with energies now able to drive fusion reactions? How do we put energy into and extract energy from such plasmas? What is the interplay of charged fluid motion and magnetic fields both generated by and influencing such motion? How do we confined extremely hot plasmas and keep them stable?

Image attribution: File:Schematic-of-a-tokamak-chamber-and-magnetic-profile.jpg: S. Li, H. Jiang, Z. Ren, C. Xuderivative work: MikeRun, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons