LPP and Warsaw Results

Posted by Rezwan on Feb 10, 2011 at 04:12 PM
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The whole report as a pdf

Our new results, together with research results from a colleague working with the world’s largest DPF device in Warsaw, Poland, have helped us to gain a greater understanding of the three-step process that leads to higher density and nuclear fusions within the plasmoids.

The first clue came from a new paper by Kubes et al in IEEE Transactions on Plasma Science. The paper shows sequences of images that they obtained in Warsaw for single shots using a laser interferometer (Figure 4). The images have much lower resolution than our ICCD images, but they have accurate timing and they show shapes that very much resemble the ones we are getting. The key thing learned from them is that the images we have seen with a plasmoid near the bottom of our viewing area, away from the end of the anode, are not a different type of pinch, but are a later stage than the helix-kink we see forming very near the anode hole. In fact the plasmoid is still forming as it moves away from the anode, as confirmed by our January 24th image.

A second clue from our January 24th image is in the bright dots scattered over the un-processed image (at left in Figure 3, shown at larger size for clarity here in Figure 5). These are scattered X-rays which have bounced around the lead shield protecting the ICCD. (We have now reinforced the camera’s shielding.) This shows that the X-ray pulse was still being produced when the image was taken, and is a big help in making our knowledge of the ICCD camera’s delay relative to the other detectors more precise. Since in this shot, as in all the long-pinch-time shots (LPTs) where the fusion pulse comes 30-60 ns after the last X-ray pulse, the fusion reactions come later than this image, when the plasmoid is presumed to be denser.

If we put these clues together with our information from the beam shot, that the beams comes at the same time as the first two X-ray pulses, we have a better picture of what is going on in the LPTs, which do not produce as much fusion yield as we expect. There is no pre-shock as we had thought, and energy is transferred efficiently into the plasmoid. However, since the beam is produced too early, it drains the energy from his plasmoid before it has time to fully compress itself and achieve the high density needed for high yield.

One further clue as to why the LPTs are less than ideal comes in the images we have taken of the current sheath, which show little or no filamentation compared with our earlier shots. This lack of filamentation may reduce the plasma density early in the plasmoid formation process, allowing radiation to escape from spiraling electrons, a process that leads to beam generation.

So far we have not yet succeeded in producing further SPTs, those shots where the pinch occurs early enough so that the current is still rising. These are the shots that achieve greatest density.

While we have made big strides this month in understanding what is going on, we still don’t clearly see why there are three distinct stages, and three X-ray pulses. We also need to find out why we see the beam signal so rarely—presumably because is not often aimed directly along the axis where the URC sits.

Our next set of experiments should illuminate both these questions further.