The fusion reaction going on inside a star is catalyzed by the pressure of several hundred thousand kilometres of hydrogen and helium pushing in from all directions. The fusion reaction going on inside a fusion generator is catalyzed by lasers, magnetic fields, and the containment of special vessels. These two very different ways of achieving roughly the same goal (of taking two single-proton hydrogens and making a single two-proton helium) can still learn a lot from one another, however.
Research in lab-based fusion can influence our understanding of star-fusion, and lead cosmologists down different research paths when scanning the sky. The small-scale detail allowed by a laboratory fusion setup can often be extrapolated to predict behavior on the scale of a star, and that’s just what new researchfrom Princeton and the University of Michigan does.
The researchers have been studying fusion power for some time, particularly a type of fusion referred to as “inertial confinement” fusion. This uses lasers to compress a small, spherical sample of fuel until its inner portion essentially implodes; the implosion generates the incredible heat necessary to achieve “ignition,” or to kickstart the fusion process.
The biggest problem with this is that compressing a spherical sample by close to 50 times is difficult to do uniformly, and even precision lasers have trouble compressing the fuel pellet precisely the same way in all directions. Even a slight imperfection in the compression shape, slight deviations in the amount of compression done from all directions over a very specific span of time, can dramatically affect the quality of the final reaction.
The top half shows heat distribution early in the process, the bottom later on. Notice that in the top half there is no chance for electrons to jump between hotspots. On the bottom, the two meld together and allow heat flow.
However the push of these lasers causes a portion of the sample to become a plasma — a fourth state of matter in which the subatomic particles of atoms dissociate and move freely. In this state, electrons from the sample begin to circulate, and by moving create a magnetic field that can affect how the compression process plays out. By studying the magnetic implications of this electron flow, the researchers think they can refine the laser-compression process to make fusion much, much more efficient. As we reported last month, while fusion is beginning to reach parity for energy absorbs vs. energy produced, the energy absorbed by a fuel pellet is still only around 1% of the total energy directed at the pellet. The pellet, which is composed of heavy hydrogen isotopes deuterium and tritium, must absorb most or all of this energy for fusion to be an eligible mass-power solution.
A more efficient system of compression could be the key to making the fusion process consume less power than it creates — which is the whole idea. Their studies into the movement of electrons during the confinement process shows that by creating a magnetic field, electrons can affect the lasers and break uniformity in the compressing laser shell. If true, this could help to explain why fusion has had such trouble creating highly efficient implosions with lasers, and it could allow scientists to design a laser array to work with magnetic flux rather than against it.
The sample, in a cylinder of gold, is just a few millimetres across.
However, the research also has implications for astronomical events like solar flares, since the movement of so many plasma-borne electrons could easily affect the timing, direction, and intensity of a solar flare. At present we can only predict many such events by doing frequency analysis, predicting the likelihood of a flare in April by looking at the past numbers for flares in April. However, a more mechanistic understanding of solar activity could allow intelligent monitoring and early warning systems, cameras that follow magnetic flux over the surface of the sun and watch as flares and other anomalies form.
The principle of “magnetic reconnection” is the blame here, which describes the ability of highly conductive plasmas to convert magnetic energy into kinetic and thermal energy. This research basically posits a new path on which reconnection can take place, and thus a possible new model for scientists to use in understanding and predicting its effects.
This is an interesting piece of research regardless of its real-world implications, since it puts on display a totally novel (if highly specific) sort of quantum behavior — and as with most fundamental research, we are already seeing that such supposedly useless knowledge can open doors and close arguments across the entire breadth of science.
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