Naked Science Forum
Non Life Sciences => Technology => Topic started by: RayG on 23/02/2022 14:06:15
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I recently heard about the JET Fusion Reactor and the latest "promising" experiment. I've known that they have been working on these things for many years. One thing that has peaked my curiosity is the temperatures they are working with. 100-150 million degrees and "TEN TIMES THE TEMPERATURE OF THE CENTER OF THE SUN!!!". JET is using Tritium, Deuterium and Beryllium in their work which are much heavier elements. The amount of power needed to generate 150 million degrees and the pressure required is enormous! For enough juice to boil 60 kettles for 5 seconds?
Why not do as the Sun does? Convert H to He at the temperature/pressure of the center of the Sun. The Sun seems to do okay with that amount of temperature and pressure, and has done for about 4.5 Billion years.
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Why not do as the Sun does?
As I understand it, the sun has much greater pressures at its core than we can achieve, but we can jack the temperature up to compensate.
Even with this "promising result," I'm still not convinced that fusion reactors on earth is a good idea. Even if we can get a fusion reaction to release more energy than was required to reach ignition, I don't think we have a good way to use that energy efficiently. It's an awful lot of capital expenditure and complex working parts to make what is effectively a heat generator...
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Surely the heat of fusion is defined and is a specific ammount?
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Why not do as the Sun does? Convert H to He at the temperature/pressure of the center of the Sun.
There is no way to generate and maintain that pressure in the reaction chamber.
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My father worked for the UK Central Electricity Generating Board when we had a proper nationalised electricity supply with a strategic energy reserve. At the time, they were considering adding nuclear reactors against the day when the coal ran out (and it has - there is still over 100 years' supply in the ground but Margaret Thatcher rendered it inaccessible and made us the slaves of Russia). He attended a comprehensive course on nuclear reactor engineering and concluded "it's a very complicated way of boiling water".
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The Lawson Criterion links the density, temperature and duration of plasma confinement to the ability to produce useful power.
The center of the Sun has a hydrogen plasma with a density of around 150g/ml, or 150x the density of liquid water.
- Some ways to produce fusion energy (eg in a hydrogen bomb) use intense radiation (eg from a uranium bomb) to compress solid fuel to get very high densities to initiate fusion.
- But you would not want one of these in the next suburb!
- JET (last generation research reactor) and ITER (next generation research reactor) try to do this in a more repeatable way...
https://en.wikipedia.org/wiki/Lawson_criterion
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On a weight for weight basis, the Sun produces power at about the same rate as a compost heap.
To be any use, we have to get the reaction to go a lot faster
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I have slept on a compost heap. Very cosy. I wasn't drunk, just lost on a mountain at night. Now that's green energy for you.