First ICCD image of plasmoid at FF-1
On June 30, LPP got their first ICCD camera image of a newly-born plasmoid.
Per Eric Lerner,
Fred Van Roessel, our part-time engineer, was able to set up optics to correctly focus the ICCD and shielding so that it would be adequately protected against FF-1’s powerful radio noise.
Since our continuing switch problems made it difficult to predict exactly when the plasmoid would form in a particular shot, we knew we would have to wait for a few shots to see one.
But on our first day of full functioning with the ICCD, we got our first picture of a plasmoid on shot 14. (This was a relatively small shot with a late pinch due to too much fill gas, or too little current for the gas. The current was 600 kA with 20 torr fill.) The image , Figure 1, slightly contrast-enhanced, is taken directly side-on, perpendicular to the axis of the device through the quartz view window.
The dark rectangular shadows at the top are two of the 3/8-inch cathode rods. The bright line across the image, separating the light from the dark areas, is the plasma sheath.
The plasmoid, the bright spot, can be seen at the tip of the twisted and kinking pinch column. The image gives evidence of the kinking which we and others feel leads to the plasmoid formation. It also gives a maximum radius for the plasmoid of about 700 microns. The plasmoid itself is smaller, and is buried within the bright spot.
Unfortunately we are still learning to use the software, and some data within the spot was lost when the image was saved. In addition, the ICCD observes the plasmoid in UV light, so may not be able to see all the way into the densest parts. We are working to get better images in the future. We intend to tilt the camera a bit so that we are viewing the pinch area at a slight angle, which will better enable us to see the filamentary structure in the sheath.
For visual reference, the dark rectangles are the electrodes and the light area is the sheathe of plasma and filaments. Compare that with the artists (Torulf’s) rendition of the electrodes and filaments:
And actual electrodes with a digital camera: