First ICCD image of plasmoid at FF-1

Posted by Rezwan on Jul 29, 2010 at 08:17 AM
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On June 30, LPP got their first ICCD camera image of a newly-born plasmoid.

Figure 1.  Image of plasmoid and plasma sheath

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: 

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There are (6) comments.

What is the sheath attached to in the photo, if the dark rectangles are the electrodes?


willit's avatar

looks like an ultrasound of a plasmoid in fetal position.  boy or girl?  can’t wait untill it grows up.

Wonderful perspective, willit!

And it’s wonderful to be witnesses to this history.

Thanks Mr. Van Roessel, EJL, and all the LPPX Group!

-John Malone

Rezwan's avatar

That’s great Willit!  It’s a plasmoid : )

Yes, Tulse, the dark rectangles are electrodes.  I had hoped the follow-up pictures would make it clear.  In Torulf’s image you get the idea - the blue umbrella coming off the electrodes are the plasma sheathe.  One day a fine animator will superimpose these images and it will all make sense.

Oh, wait.  Your Q is what is the sheathe attached to.  I think the animation makes it clear - the filaments of plasma jump across the electrodes and connect to each other and it gets that jellyfish form.  The sheathe and filaments are all spilling off, like water from a fountain that has magnetic attraction.

Rezwan's avatar

One day, far in phase 2, when they have the thing pulsing, it will be more like an ultrasound, with the “heartbeat”.

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