These new images from inside our Focus-Fusion-2B experimental device show the development of the filaments of current (bright thin parallel lines) in the early stages of each pulse. The filaments are a crucial step in compressing and heating the plasma to get fusion reactions. The images, taken with our ICCD camera using an exposure time of only 5 ns (billionths of a second) show the current sheath moving down the anode (towards upper right) as viewed between the cathode vanes (diagonal black bands). The top-to-bottom size of the images is 2.5 cm.
They show the development of the sheath from 230-570 ns after the current starts flowing. So, the events are happening about 6 million times faster than you see them in this GIF. The key positive features of the images are that the filaments (running from lower left towards upper right) are evenly spaced and thin—only 200 microns in radius. Those characteristics should lead to a dense plasmoid and rapid fusion burn. But the images also show the challenge that we currently face—the front (right) edge of the sheath is not a single, sharp line, but two separated fronts. This is caused, we know, by the oscillation in current that produces an early small pulse of current, followed by a bigger one. In the region between the fronts the filaments are twisted and disorganized. This leads to poor compression and less fusion. However, we are working hard to eliminate the oscillations so there is a single front and the filaments will be neatly organized all the way to the front of the sheath. In the past three months, we have achieved significant progress in greatly reducing the oscillations, but have not yet reached the threshold for a new increase in yield.
These images are produced from 10 separate, but very similar, shots. The flickers in brightness are caused by changes in camera filters and sensitivity—the real brightness is steadily increasing during the time covered as the current flowing through the sheath increases.