Fusion Energy on the Horizon? Again?

The big news recently as reported in Nature (13 December) was that researchers at the US National Ignition Facility carried out a reaction that made more energy than was put in. That looks great, right? The energy crisis is solved. Not so fast. What actually happened was that 192 lasers delivered 2.05 MJ of energy onto a pea-sized gold cylinder containing a frozen pellet of deuterium and tritium. The reason for all the lasers was to ensure that the input energy was symmetrical, and that caused the capsule to collapse under pressures and temperatures only seen in stars, and thermonuclear weapons. The hydrogen isotopes fused into helium, releasing additional energy and creating a cascade of fusion reactions. The laboratory claimed the reaction released 3.15 MJ of energy, roughly 54% more than was delivered by the lasers, and double the previous record of 1.3 MJ.

Unfortunately, the situation is a little less rosy than that might appear. While the actual reaction was a net energy producer based on the energy input to the hydrogen, the lasers were consuming power even when not firing at the hydrogen, and between start-up and shut-down they consumed 322 MJ of energy. So while more energy came out of the target than went in to compress it, if we count the additional energy consumed elsewhere but necessary to do the experiment, then slightly less than 1% of what went in came out. That is not such a roaring success. However, before we get critical, the setup was not designed to produce power. Rather it was designed to produce data to better understand what is required to achieve fusion. That is the platitudinal answer. The real reason was to help nuclear weapons scientists understand what happens with the intense heat and pressure of a fusion reaction. So the first question is, “What next?” Weapons research, or contribute towards fusion energy for peaceful purposes?

Ther next question is, will this approach contribute to an energy program. If we stop and think, the gold pellet of frozen deuterium had to be inserted, then everything line up for a concentrated burst. You get a burst of heat, but we still only got 3 MJ of heat. You may be quite fortunate to convert that to 1 MJ of electricity. Now, if it takes, say, a thousand second before you can fire up the next capsule, you have 1 kW of power. Would what you sell that for pay for the gold capsule consumption?

That raises the question, how do you convert the heat to electricity? The most common answer offered appears to be to use it to boil water and use the steam to drive a turbine. A smarter way might be to use magnetohydrodynamics. The concept is the hot gas is made to generate a high velocity plasma, and as that is slowed down, the kinetic energy of the plasma is converted to electricity. The Russians tried to make electricity this way by burning coal in oxygen to make a plasma at about 4000 degrees K. The theoretical maximum energy U is given by

    U  =  (T – T*)/T

where T is the maximum temperature and T* is the temperature when the plasma degrades and the extraction of further electricity is impossible. As you can see, it was possible to get approximately 60% energy conversion. Ultimately, this power source failed, mainly because the cola produces a slag which damaged the electrodes. In theory, the energy could be drawn in almost 100 % efficiency.

Once the recovery of energy is solved, there remains then problem of increasing the burn rate. Waiting for everything to cool down then adding an additional pellet cannot work, but expecting a pellet of hydrogen to remain in the condensed form when inserted into a temperature of, say, a million degrees, is asking a lot.

This will be my last post for the year, so let me wish you all a Very Merry Christmas, and a prosperous and successful New Year. I shall post again in mid-January, after a summer vacation.

Meanwhile, for any who fell they have an interest in physics, in the Facebook Theoretical Physics group, I am posting a series that demonstrates why this year’s Nobel Prize was wrongly assigned as Alain Aspect did not demonstrate violations of Bell’s inequality. Your challenge, for the Christmas period, is to prove me wrong and stand up for the Swedish Academy. If it is too difficult to find, I may post the sequence here if there were interest.

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Ebook Discount

From December 15 – January 1, the summer Smashwords sale,  my ebooks at Smashwords will be significantly discounted. The fictional ebooks include”

Puppeteer:  A technothriller where governance is breaking down due to government debt, and where a terrorist attack threatens to kill tens to hundreds of millions of people and destroy billions of dollars worth of infrastructure.

http://www.smashwords.com/books/view/69696

‘Bot War:  A technothriller set about 8 years later, a more concerted series of terrorist attacks made by stolen drones lead to partial governance breaking down.

Smashwords    https://www.smashwords.com/books/view/677836

Troubles. Dystopian, set about 10 years later still, the world is emerging from anarchy, and there is a scramble to control the assets. Some are just plain greedy, some think corporate efficiency should rule, some think the individual should have the right to thrive, some think democracy should prevail as long as they can rig it, while the gun is the final arbiter.

https://www.smashwords.com/books/view/174203

There is also the non-fictional “Biofuels”. This gives an overview of the issues involved in biofuels having an impact on climate change. Given that electric vehicles, over their lifetime probably have an environmental impact equivalent to or greater than the combustion motor, given that we might want to continue to fly, and given that the carbon from a combustion exhaust offers no increase in atmospheric carbon levels if it came from biofuel, you might be interested to see what potential this has. The author was involved in research on this intermittently (i.e. when there was a crisis and funding was available) for over thirty years. https://www.smashwords.com/books/view/454344

Finally, I am offering a discount on “Planetary Formation and Biogenesis”. This explains why our solar system has the properties it has, it has about 1280 scientific references, and this will probably be the only time it is discounted. https://www.smashwords.com/books/view/1148194

Solar Cycles

As you may know, our sun has a solar cycle of about 11 years, and during that time the sun’s magnetic field changes, oscillating between very strong then there is a minimum, then back to the next cycle. During the minimum, there are far fewer sunspots, and the power output is also at a minimum. The last minimum started about 2017, so now we can expect increased activity. It may come as something of a disappointment that some of the peak temperatures here happened during solar minima as we can expect that the next few years will be even hotter and the effects of climate change more dramatic, but that is not what this post is about. The question is, is out sun a typical star, or is it unusual?

That raises the question, if it were unusual, how can we tell?

The power output may vary, but not extremely. The output generally is reasonably constant. We can attribute the variation in the solar output we receive over different years of about 0.1% of a degree Kelvin (or Centigrade) to that. There may appear to be more greater changes as the frequency and strength of aurorae are more significant. So how do we tell whether other stars have similar cycles? As you might guess, the power input from other stars is trivial compared even with that small variation. Any variation in total power output would be extremely difficult to detect, especially over time since instrument calibration could easily vary by more. A non-scientist may have trouble with this statement, but it would be extremely difficult to make a sensitive instrument that would record a dead flat line for a tiny constant power source over an eleven-year period. Over shorter time periods the power input from a star does vary in a clearly detectable way, and has been the basis of the Kepler telescope detecting planets.

However, as outlined in Physics World (April 5) there is a way to detect changes in magnetic fields. Stars are so hot they ionize elements, and some absorption lines in the spectrum due to ionized calcium happen to be sensitive to the stellar magnetic field. One survey showed that about half the stars surveyed appeared to have such starspot cycles, and the periodic time could be measured for half of those with the cycles. It should be noted that the inability to detect the lines does not mean the star does not have such a cycle; it may mean that, working at the limits of detection anyway, the signals were too weak to be certain of their presence.

The average length of the length of such solar cycles was about ten years, which is similar to our sun’s eleven-year cycle, although one star had a cycle lasting four years. One star, HD 166620 had a cycle seventeen years long, although “had” is the operative tense. From somewhere between 1995 and 2004, HD 166620’s starspot cycle simply turned off. (The uncertainty in the timing was because the study was discontinued due to a change of observatories, and it changed to one receiving an upgrade that was not completed until 2004.) We now await it starting up again.

Maybe that could be a long wait. In 1645 the Sun entered what we call the Maunder minimum. During the bottom of a solar cycle we would expect at least a dozen or so sunspots per year, and at the maximum, over 100. Between 1672 and 1699 fewer than 50 sunspots were observed. It appeared that for about 70 years the sun’s magnetic field was mostly turned off. So maybe HD 166620 is sustaining a similar minimum. Maybe there is a planet with citizens complaining about the cold.

What causes that? Interestingly, (Metcalfe et al. Astrophys. J. Lett. 826 L2 2016) showed that by correlating stellar rotation with age for stars older than the sun, while stars start out spinning rapidly, magnetic braking gradually slows them down, and as they slow it is argued that Maunder Minimum events may become more regular, and eventually the star slows sufficiently that the dynamo effect is insufficient and they enter a grand minimum. So eventually the Sun’s magnetic dynamo may shut down completely. Apparently, some stars display somewhat chaotic activity, some have spells of lethargy, thus HD 101501 shut down between 1980 – 1990, before reactivating, a rather short Maunder Minimum.

So when you hear people say the sun is just an average sort of star, they are fairly close to the truth. But when you hear them say the power output will steadily increase, that may not be exactly correct.

Ancient Birds

You probably have never heard of Janavis finalidens. It was a bird with webbed feet and a body vaguely reminiscent of a wild hen. It would have been the size approximating to a grey heron and had a mass estimated to be 1.5 kg. I use the past tense because it lived in the late Cretaceous, so birds had evolved away from the therapods well before the extinction. This bird was, in shape, very similar to modern birds, which is hardly surprising because flight puts limits on them, but there is one notable difference: the beak was lined with teeth. We do not know a lot about them, in part because their bones are rather fragile and more difficult to fossilize, but maybe also because they are not so spectacular as the monster dinosaurs of the time. This particular example was found a couple of decades ago in a quarry, and when it was worked out what it was, it was filed.

However, more modern equipment, specifically micro-computed tomography, has re-examined the samples. Originally, they thought they had a handful of bones from the spine, wings, shoulders and legs. However, one of the bones they thought had been a shoulder bone was a pterygoid, a bone from the bony palate of the skull.

Most current birds belong to a group called neognaths, which means “new jaws”. The key bones here are mobile, and they allow the birds to move the upper beak independently of the skull. There is a small group of birds, the emu, cassowary, ostrich, kiwi and tinamous (47 species, ground dwelling, but some can fly) have the bones in the upper palate fused together. These are also called paleognaths, or “ancient jaws”. You will probably suspect from this naming that it was believed that birds originally came with these fused jaws, but most subsequently evolved the ability to move the upper beak. In this context, non-avian dinosaurs also have fused palates, and the last common ancestor of all modern birds lived some 80 million years ago, so it would be reasonable to assume that it had a fixed palate like the other dinosaurs. Unfortunately, this is one of those theories that is hard to test because the small delicate pterygoid is usually missing from the fossils.

However, a recent article in Nature (Benito et al., vol 612, pp 100 – 105) indicated that Janavis‘ pterygoid “probably formed part of an unfused bony palate”. That means the upper beak was probably mobile. Note the uncomfortable “probably”. The resemblance of the pterygoid to that of modern chickens now suggests that the mobile upper beak evolved first, and the fused beaks arose later. That, of course, raises the question, how did it evolve, and why did some birds revert to the fused palate.

How the beak functions is crucially dependent on the bones of the upper palate. By unfusing it, it increases the flexibility of the beak and improves the use of the beak. However, fused palates are not necessarily a drawback, and might give beaks of larger birds additional support. For the kiwi, the beak is extremely long compared with the bird, and fusing the upper beak to the skull might give it more strength as it probes logs for food (often grubs in decaying logs). It might also be of interest that these birds, being flightless, tend to get most of their food from the ground, including plant material, but then again so do hens.

Accordingly, if you are concerned with the evolution of birds, admittedly not a common concern, you now have a problem, and the question is, how do you solve it? One way is to find plenty of fossils, but the difficulty is first, they are rare, and secondly, we have many samples from times when both were present, including now. How do you know you are not being misled? An important aspect of science is that once you have a reasonably well-defined problem and a possible solution, you can arrive at ways of testing it. One of the peculiarities of evolution is that as an egg grows to the adult, it often gives clues as to the evolutionary path it took. The most obvious example is the frog, first going through the tadpole stage. In the case of modern paleognaths, one approach being considered is look at their development stages. If there are differences, this would be a clue that the trait arose independently more than once.