With many of the lab members away at a conference this week, I was able to run some experiments over the past weekend. While this is not as detailed an experiment as can be performed during a full run week, every little bit helps. We tried some new setups and took some photos that are on display below. All three images (it's actually two images, the duplicate is labeled in its second presentation) are from one end of the LAPD and view the entire 16.6 meter (m) plasma length. This view makes it difficult to provide perspective on the distances between objects.

The first photo shows just about everything that constitutes my experiment:

• Plasma: all of the pinkish-whitish haze is plasma. This is a helium plasma.
  
  
• Electron Beam Structure: the fuzzy object at the top-center. We cannot see the emission crystal of the beam because it is pointed away from the camera. It is out of focus because it is approximately 2.24 m away from the focus position.
  
  
• Langmuir Probes: two dark items coming in horizontally from the left. These are the primary measurement tools and some detail of them, though not necessarily these exact ones, may be seen here and here. They are positioned at the same vertical location and 1.28 m apart horizontally.
  
  
• Heated Plasma Filament: snaky line going from the electron beam source, through the probes, and disappearing into the plasma center. This (partially described in my thesis overview) is a narrow region of plasma that has been heated by the energetic electrons of the beam.
  
  
• Mesh: not labeled, this is seen everywhere and might look like poor resolution or out of focus areas. There is a conducting grid behind the electron beam but still inside the vacuum chamber. It helps define the boundary conditions for some experiments.
  
  

An LAPD plasma during an electron heat transport experiment.

The very bright filament is achieved by turning up the power on the electron beam. My thesis experiment focuses on heat transport by minimizing density perturbations. In this image, however, the beam is of great enough energy that it ionizes gas itself and causes large density perturbations. This exercise is not completely useless because in addition to the fun pictures I also get a data set that demonstrates the behavior of the system in the presence of beam generated density.

The plasma image is labeled to highlight the electron beam, Langmuir probes, and heated filament.

The final image is provided as a reference. In it, the electron beam structure is still in the plasma, but the beam is turned off. The probes have been removed. The default alignment of the camera does not view the electron beam structure, so I pushed it over by hand to snap these photos. If it were fixed in position, then these images would represent exactly the same space and could be subtracted to better determine the perturbation of the heating. That would be interesting so maybe I'll plan on it for the next data run.

An LAPD plasma without an experiment running.

Tags: thesis experiment, experimental plasma physics