What is Nuclear Fusion?

What is nuclear fusion? Many of us might have heard the term kicked around before but do we know what it means. We go back to the basics...
02 September 2014

Interview with 

Brian Fulton, the University of York


All around the world, countries are trying to come up with new ways to power their cities, cars and homes. Energy consumption is a growing problem as our demand for power increases to keep up with our busy lifestyles. At the moment, we are reliant on fossil fuels, but these are rapidly running out, and polluting our environment. Another option may be nuclear fusion. Scientists have been promising us clean, unlimited energy from seawater for the past 60 years, but it hasn't yet materialised. Could it be the answer? Lets look at the basics, what actually is nuclear fusion? Many of us might have heard the term kicked around before but do we know what it means. Professor Brian Fulton, from the physics department at York University, explained it to Dave Ansell... sun fusion

Brian -   Nuclear fusion is the process where we take a couple of small nuclei in the sun where it happens.  We have hydrogen nuclei and we push them together so they join, hence, the term 'fusion'.

Dave -   So, the nuclei are the little tiny positive bits in the middle of an atom.

Brian -   They are, yes.  In the sun which is a big ball of hydrogen, the temperature is so hot that the electrons that normally orbit around the nucleus have been knocked off.  So, we have bare nuclei, bare protons which is the nucleus of hydrogen.

Dave -   So, these are somehow joining together.  How does that actually work?

Brian -   In the sun, which is a large ball of gas - in a gas, the atoms rush around.  The higher the temperature, the more they rush around.  And they're continually colliding against each other.  And if we heat the gas up sufficiently then the nuclei will collide so violently that they will fuse together.  It's not an easy task because each nucleus has a little positive charge on it.  As we remember from our school days, positive charges repel.  So, it takes a lot of effort to get the two little nuclei to come close together because we're pushing them against that electrostatic repulsion.  But if we get the temperature high enough, they'll collide violently enough that they'll get close enough, and they'll fuse together.

Dave -   I guess it's quite a good thing that this isn't too easy because otherwise, the sun would kind of burn out very quickly I guess.

Brian -   It would, yes.  The sun is doing this all the time, that's where all our energy comes from.  In fact, the sun is turning about every second, about 1 billion tons of hydrogen, is transformed to helium through that process and that's what produced the energy which keeps us alive here on Earth.

Dave -   That sounds like a lot.  I guess the sun is very, very large.

Brian -   The sun is pretty big.  It's going to be around there for a few billion years more.

Dave -   So, how come the sun is going to sit there for 5 billion years stably.  Is there anything which is stopping it either exploding or kind of fizzling out?

Brian -   The sun is in a state of equilibrium at the moment.  The nuclear energy at the centre is heating it up and trying to push it out and expand it like any gas stoves when you heat it.  But gravity of course is there as well.  Since the sun is such a huge enormous object, gravity is very strong.  So, we've got a bit of a balance at the moment for the next few billion years where the nuclear energy will be just enough to stop gravity compressing the sun.  But in a few billion years, once the nuclear fuel in the centre of the sun runs out, then that's it I'm afraid.

Dave -   So, if it's just happening naturally all the time, why is it very difficult to do on Earth?

Brian -   The problem here on Earth is that the temperature required for this gas to be moving around this hydrogen is several million degrees and it's very hard to contain that gas.  You can't put it inside a container because we don't have anything that will survive temperatures a few million degrees.  So, we have to find other clever ways of containing that gas.  And magnetic confinement is currently the best option, but there are other methods being looked out as well.

Dave -   So basically, the problem is, I guess if you let it expand even you had a big enough bottle then the pressure will go down and the little nuclei would stop bashing into each other and stop seeking the other and stop fusing.

Brian -   Yes, it's a balance between having the density high enough so that there are many collisions and the temperature high enough so that the collisions are violent enough to overcome that column or electrostatic repulsion.  So technologically, extremely challenging.


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