a bonobo humanity?

something to do with laser confinement fusion energy

Ways of producing nuclear fusion:

1. High-temperature superconductors (HTS) for magnetic confinement fusion.

HTS is all about producing more powerful magnets, in order to effectively confine super-hot (100 million degrees Celsius) plasma. Traditional electrically conducting materials such as copper will lose conductivity and become resistant at high temperatures, causing them to over-heat. To eliminate electrical resistance from potential superconducting materials, they need to be cooled to -269 Celsius. I’m trying to get my head around this, so I’m following the demo in the Royal Institution lecture linked below. A small but powerful magnet was dropped into a hollow copper tube, held vertically. It finally emerged from the bottom, but not at the pace of gravity. It’s all about the peculiar relationship between magnetism and electricity. The magnet creates a moving magnetic field inside the copper tube, inducing an electrical current, which, somehow, creates its own magnetic field in opposition to the field from the magnet, pushing back… (somehow I feel I should’ve done a Canto and Jacinta on this one!)

So, as the demonstrator tells us, we can vary the electrical resistance of metals, for example by increasing or reducing their temperature, as described above. Warming the copper tube increases its resistance, cooling it will decrease its resistance. A further demonstration with the same magnet and a very much cooled copper tube (-196 Celsius) showed that the magnet took longer to move down the tube. I don’t really understand how that proves decreased resistance, but then I’m no physicist… But the demonstrator explains:

 So with the reduction in the resistance of the copper, those currents are able to form and flow more easily, and therefore they have a stronger magnetic field, opposing the falling magnetic field of the magnet [my emphasis].

So that clarifies things a bit. And the aim is to remove all electrical resistance, if possible. This can’t be done with most metals, including copper. And so – superconductors. There are apparently, high-temperature superconductors and low-temperature superconductors, the latter being the ones that need to be cooled down to -269 Celsius. So the demonstrator proceeds to demonstrate the effect of a dose of liquid nitrogen on a potential HTS, described rather vaguely as a ‘ small chip of super[lux??]’. I’ve tried looking up what he meant here (the captions didn’t help), but have come up empty. I’m guessing that he’s simply doused the same ‘small but powerful’ magnet. Anyway, the doused chip sits in a polystyrene cup which is sitting on a circular magnetic track. The supercooling is designed to turn it into a HTS, presumably. The aim is to repel the field from the magnetic track ‘by setting up its own internal currents’ in balanced opposition. The chip has to be doused a couple of times with the liquid nitrogen to get it to the right temperature, but the demonstrator soon has the cup with its ‘chip’ riding on the magnetic rail like a wee whited coaltruck, back and forth with a fingerpush.

Presumably the chip will have to be kept at this temperature to maintain this internal current. It will regain its electrical resistance upon warming up to a certain point. The second demonstrator shows us a HTS tape, which, when cooled down to 20 degrees Kelvin (that’s less than -250 celsius), will carry five times its normal electric current, with no resistance. Wound into a tight coil, the material, which is super-thin, will have a much higher energy or current density, which can be used to generate a strong magnetic field. The more material in the coil, the greater the current density, until the magnetic field is strong enough to safely confine the plasma from nuclear fusion. A scaled-up version of this  type of coil is used at ITER. They require far less energy to cool them down too. Tokamak Energy is using these coils, combined with a spherical ‘cored apple’ tokamak shape, which apparently makes more effective use of the magnetic field. Altogether, a more efficient design – they hope. Developed in he UK, it’s being used also by the STEP plant (ST for Spherical Tokamak).

2. Laser fusion with diode pumps

Laser fusion is the next technology Windridge discusses. So how do lasers work? From memory, LASER stands for Light Amplification through Stimulated Emission of Radiation, but that don’t tell me much. Anyway it’s all about diode pumps. Wikipedia gives this elaboration:

A diode-pumped solid-state laser (DPSSL) is a solid-state laser made by pumping a solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a laser diode

I think I’ll stick with Windridge’s description. We see some images, first of a pink rod of ruby crystal, the ‘lasing material’, wrapped round by a coil of incandescent lighting, which sends a flash of light into the crystal, exciting its atoms and somehow generating photons, all of the same wavelength. The ruby and the coil are enclosed in a capsule, and the generated photons bounce back and forth between mirrors at either end of the capsule, triggering the release of more photons in a build-up of energy. Finally, a beam of energy emerges ‘through a partially reflective mirror at one end’. How this creates fusion energy, I’ve no idea. I vaguely get the sense of pumping but…

Here’s a useful definition of a diode from a website called Fluke:

A diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction.

It seems that the key here is to produce photons of a particular wavelength. Windridge compares a diode pump with a flash lamp or incandescent bulb. While the flash lamp produces this wide range of energies or wavelengths, but a more targeted, precisely defined energy level is all that is required to excite the crystal photons, meaning it can be done with less waste of heat-energy. Diode lasers are many times more efficient than the NIF laser, for example – nearly 40 times more efficient (the NIF laser uses flash lamps). Remember, NIF (the National Ignition Facility) made headlines some months ago by getting more energy out of their fusion experiment than they put into targeting and ‘igniting’ the fusion pellet, but critics noted that the energy needed to drive the laser was orders of magnitude greater than the energy produced. The diode pump may, if found to be workable, reduce those orders of magnitude considerably.

So, although I don’t quite understand all the details, to put it mildly. I do get a strong sense that progress is being made. We seem to have gone beyond proof of concept, and are entering the engineering phase, and it looks like the next couple of decades will some exciting results. Tritium breeding and handling (it’s extremely rare and radioactive) is a big issue, and new materials science will be required to deal with high-energy neutrons and the damage they cause. Producing and testing such materials will be a high priority, but the pay-off can hardly be calculated. High-temperature superconductors are a relatively new development, and perhaps more breakthroughs can be made there. With more money being poured in, there will be more jobs for smart people – can-do problem solvers.

So, after watching this video a couple of times and trying with limited success to understand the science, but understanding enough to be aware of the viability of something that once would have seemed the most impossible of dreams – replicating the vast power of the stars – I read  many of the comments, and was dismayed by the high level of negativity. An almost ferocious naysaying. I could respond with Kafka’s ‘genius doesn’t complain, but runs straight against the wind’, or ‘We choose to go to the moon, not because it is easy but because it is hard’, by that Kennedy bloke. It was just a little less than a century ago that Hubble provided convincing evidence that other galaxies existed. Two centuries ago we knew nothing of atoms or genes or space-time. The progress we’ve made science since then is – well, astronomical. Of course, new breakthroughs tend to create new problems, and I can imagine science-fiction scenarios in which our play with fusion ends up in our going up in a sunburst of glory – ‘Out, brief candle!’

We shall see. I hope I can live so long…

References

Could nuclear fusion energy power the future? – with Melanie Windridge (Royal Institution lecture)

https://en.wikipedia.org/wiki/Diode-pumped_solid-state_laser

https://www.fluke.com/en-au/learn/blog/electrical/what-is-a-diode