FR2.1:Fractional ionization in LTPS
Challenge: To understand how collisions modify the transport and stability properties of LTP under conditions from weakly- to fully-ionized.
Background: Plasmas dominated by neutral or Coulomb collisions can have very different properties in terms of energy dissipation and the formation of collective phenomena. In regimes that extend from the 40 heating of plasmas in the solar corona,14,15 to controlling plasma-wall interactions in fusion plasmas,16,17 to understanding ionization processes in plasma manufacturing,18 a critical parameter for defining plasma dynamics is the degree of ionization19. In unmagnetized LTPs, varying the input power and neutral gas densities will produce fractional ionization regimes from 10-8 to 10-4, examples of which include RF/DC/microwave produced plasmas through atmospheric pressure plasmas (APP). With the inclusion of both magnetic field strength and agnetic geometry effects, it is possible to explore fractional ionization regimes where the plasma collisionality can extend from neutral collision ominated regimes (f ≤10-3) to Coulomb collision dominated regimes (f ~ 1); i.e., representing a wide range of space-relevant phenomena.
Proposed research: We will use the ability to “dial-in” fractional ionization conditions from f = 10-6 to 1 on three-dimensional magnetic surfaces to explore the effects of neutral and Coulomb collisions on plasma collective phenomena including current flow, wave propagation, and magnetic reconnection.
- Studies of collisionality in three-dimensional magnetic fields: The Compact Toroidal Hybrid (CTH) device at Auburn has the ability to form complex, closed three-dimensional magnetic field structures with geometries that can approximate regions of EM wave propagation magnetic
reconnection in geospace and heliospheric regions in scaling experiments. - Complementary studies on ALEXIS, a linear plasma device, will be used to calibrate spectroscopic measurements, benchmark probe diagnostics, and test plasma source development.
- Measurements will focus on the use of emission spectroscopy to measure the neutral content, electron density, and electron temperature from both survey and high-resolution spectrometers.
- Laboratory studies will be used to validate kinetic studies of plasmas described in FR1.1.
Integration with Transformational Technology: This work will support TT1-5 by providing the opportunity to scale between the laboratory, space, and plasma application regimes. Scaling: use the CTH device to scale its collisionality to represent regimes that extend from radiation belt conditions to the lower regions in the ionosphere (TT5) while also overlapping with a variety of industrial plasma devices, e.g., microwave and RF sources (TT1-4), and leveraging the ability to study 1-, 2-, and 3-D magnetic geometries.
Impact: Characterizing the role of collisions is one of the most challenging fundamental problems in PSE. This work will use the unique experimental capabilities available to FTPP to advance this area of research. Validation: will use collisional effects in models developed in FR1 or in the broader LTP community 20,21,22 to understand, in the spatial domain, the competition between the mean free path and other relevant plasma scales (e.g., the gyroradii, Debye lengths) and, in the temporal domain, the relationship between the collision frequencies (ion-ion, ion-neutral, electron-ion, etc.) and cyclotron frequencies. Measurements: will use emission spectroscopy to measure the neutral content, electron density, and electron temperature from both survey and high-resolution spectrometers.