Hands-on, part 3

Part a

Try to use ParaView to visualize fields. Here’s a sugggestion: Choose the simulation with most frequent output of VTK files (the sixth simulation). This should also have a drift velocity. Then,

• Open the last pictetra*.vtk , and plot the potential in a 2D slice perpendicular to the drift velocity (and the cylinder).
• Make a line plot of the electric potential along the flow direction.
• Make an animation like the one below:
  • Open the entire group pictetra*.vtk
  • Make a 2D slize of the volumetric data, and then clip the slice twice to get an upper and lower half.
  • Choose to visualize the electron density and ion density in the two halves.
  • Open the entire group scc*.vtk, and choose to visualize the surface current density.
  • Hit play to animate.
  • Tune the colorbars as you find appropriate.

This particular animation is of a 0.5-Debye-length sphere at 1V. Your animation may be different.

Part b

Use Python and Langmuir to plot the IV characteristic of the object according to the OML theory (spherical assignment) or finite length theory (cylindrical assignment) for the Oxygen plasma representative of the F-layer:

plasma = [Electron(n=1e11, T=1000),
          Oxygen(n=1e11, T=1000)]

-1V to 4V is a good range of voltages. Once you have done that, plot one marker (or “dot”) for each of the three simulations with fixed voltages on top of the IV-characteristic from Langmuir (it looks best if there’s no line connecting the dots). The steady-state currents can be found by reading pictetra.hst for the simulations, taking the exponential moving average, and using the last sample after averaging. Presumably, some functions in func.py can be reused. See func.py and plot.py for examples.

Include also a marker for the floating potential simulation. In this case the voltage must be read from pictetra.hst, preferrably by taking the last sample after averaging. (For simplicity, it might be an option to read the voltage from pictetra.hst for all four simulations).

Questions:

• Do the simulated currents agree with theory/past results?
• The floating potential according to Langmuir is where the IV-curve intersects the x-axis (you can see it if you zoom up). What is the floating potential obtained from Langmuir as well as from PTetra? Do they agree? Explain.