DIY Fusion Design 101?

Can’t touch! Won’t touch!

If you can’t touch it, how are you going to use it?

BBC had a piece in early August 2013 on ITER or the International Thermo-nuclear Experimental Reactor. This is the new, globally international project, similar in size to CERN based in the south of France, to develop fusion power.

OK. Let’s assume that we can get fusion to work for a useful period. How are we going to get the [expletive deleted] energy out?

Are you listening to me, ITER? Course they aren’t. Engineers and scientists have been working on the myriad problems for more that 50yrs. They don’t need the help of The Lad. But some students, general public and certainly the meejah might.

Here’s an engineer, The Lad, putting his head on the block. He is venturing into an engineering place in which he has no specific expertise: no change there then.  He just thinks in general terms of engineering forces. At least this is more than do most bloggers and general media. Remember, it is the working with physical forces that defines an engineer.

Fusion will only occur at temperatures that transform anything into stellar plasma. That includes ANY solid structure trying to contain it. Such energy by transmission of heat, in quantities difficult to imagine, will sublime any structure that it contacts.

Here is what happens now for most of today’s prime movers. There are several heat sources in current use; such as oil, gas, coal, wood and nuclear fission. This heat source drives the heat energy by conduction; moving energy by interaction between atomic particles. The energy passes through a pipe wall so as to heat water or gas or some other intermediary. This expands and drives a turbine or piston engine or hurtles out of the back of a jet engine generating a useful reaction.

OK. It’s currently impossibly difficult to get fusion to stay ‘alight’ for more than split seconds [or am I already out-of-date?]. Anyway that is the reason for the €billions being spent on ITER. If we assume that we will be able to improve on this; what then?

Now we need to get the energy out.

If we try to drive the energy though a pipe wall by conduction from a fusion plasma cloud, the pipe will melt it in a millisecond or less. So – not conduction then.

In boilers, both domestic kettles and Drax power station plant, they use conduction. Here bulk gas or liquid move themselves as well as their energy. Both bubbles and hot water rise because they are less dense than the surrounding water. This leads to mixing and heat transfer; producing steam for turbines driving the generators. Thanks, Archimedes. It so happens that this is also the way that radiators [a misnomer: they would be better called ‘convectors’] warm a room in a house.

Sorry, we cannot use convection. Why? Precisely because plasma is carefully arranged to be closely contained in a doughnut-shaped, Magnetic Bottle [part of a Tokamak machine]. This is a magnetic field that is designed precisely to stop the searing plasma from churning about where it is not wanted, i.e. touching anything solid.

Fusion reactor Magnetic Bottle
Fusion reactor Magnetic Bottle

What can be done? The Lad thought that he was asking a very difficult question. But then, it transpires, not so much. He remembered that engineers recognise three standard ways to transfer heat energy: conduction, convection and radiation.

heat transfer in the kitchen
Heat Transfer in the kitchen (c) Hilary Morgan


So if it can’t be conduction or convection what have we left? It must be radiation where heat energy is transmitted like light or radio. This is how warmth from the Great Fusion Reactor in the Sky [as Alan Partridge might refer to, of course, the Sun] gets transferred to us on Earth. There will be a ridiculously intense, thermal heat flux. Not only that though, there will be an equally ridiculous flux of nuclear radiation that will, itself, hammer at the structural integrity of the whole machine.

For ITER there is quite and impressive technical illustration here. Not a drawing,note: it’s an illustration so a lot can change.

While everybody that The Lad has seen talking about ‘limitless fusion power’ speaks of the fusion reactor generating the power, nobody seems to talk about getting out for our use. It seems to The Lad, radiation it has to be. But in detail how is quite another question. It is an equally giant problem. After all solar panels or black radiation absorbers on the roof of your house won’t hack it.

But don’t worry. Let the scientists get the physics of fusion and plasma nailed down and you can rely on the engineers to turn it into Power Stations for the benefit of us all.



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