Science Interviews


Tue, 2nd Sep 2014

Laser-Powered Fusion

Kate Lancaster, York Plasma Institute

Listen Now    Download as mp3 from the show Nuclear Fusion

Not all parties are convinced that this magnetically confined, or tokamak method, is going to be the most effective way to create nuclear fusion. Another approach is called Inertial Confinement Fusion, driven by powerful lasers. Ginny Smith spoke to Kate Lancaster, the Plasma and Fusion Industrial Officer for the York Plasma Institute...

Ginny -   So, when you say its confining itself, can you explain to me what that means because I'm finding it quite difficult to picture?

Kate -   Okay, so let me explain it in terms of laser fusion. What happens when we do laser inertial fusion is, you fire several hundred of the worlds most powerful lasers on a very tiny ball-bearing sized pellet of deuterium and tritium.  The outer layer actually heats up and expands very rapidly.  We all know Newtons third law, every reaction has an equal and opposite reaction, so, its kind of like gas coming out the back of a balloon., this balloon has to fly forward.  So, if the outer layer is heating up really rapidly, the rest of the fuel has to compress and stagnate and it just basically confines itself.

Ginny -   So, you're kind of using its own expansion to squeeze it together.

Kate -   That's exactly it, yes.

Ginny -   Now, you mentioned deuterium and tritium.  Weve been talking about hydrogen as the source of fuel, so can you tell me a bit about why you use them instead of normal hydrogen and what exactly they are?

Kate -   Well actually, magnetic confinement fusion also uses deuterium and tritium.  They're basically types of hydrogen.  So, hydrogen is basically a proton with an electron going around it.  Deuterium has a neutron in that nucleus too and tritium has two neutrons in that nucleus.  So, that's essentially just two different isotopes of hydrogen.

Ginny -   Why are they better than using the standard isotope?

Kate -   So, the sun actually turns hydrogen into helium. Its one of the most energetically favourable ways of getting fusion because you don't have to work as hard as you would if you were using hydrogen basically.

Ginny -   Does yours differ from the Tokamak approach?  You're using it to confine itself, but what else is different?

Kate -   So, the whole approach is different in that, with the Tokamak, what you're trying to do is confine a certain density for you really want to do it indefinitely.  Whereas in a laser driven fusion, what you care about is getting it to a very high density in a certain radius and that whole process only lasts a few tens of nanoseconds.  And then the second thing that's different obviously is then, you would need to do this multiple times a second in order to make that work.  So, its sort of just a completely different approach.

Ginny -   Why are there so many different approaches to nuclear fusion?  Can we not calculate which will be the best way of doing it?

Kate -   There's a myriad of ways in which you could do it, but its about the ways in which are the most energetically favourable lets say, where you're going to get the most bang for your buck.  It would be great if we could calculate it, but the fact is, we don't know all the physics yet.  So, I think that's the bottom line until we do know that, because its still very much a science project.  Were not at that stage where its just engineering problems.

Ginny -   And how close are you to actually getting net energy out of the reactions?

Kate -   So, were at a very exciting time at the moment.  There's one facility in the world currently called the National Ignition Facility (NIF) that's based at the Lawrence Livermore National Laboratory and that's the only facility that has the potential to make breakeven in laser fusion.  At the moment, they've got to the stage where the energy that's been absorbed by the fuel is less than the energy they're getting out via neutrons which is a really important stage, but its not breakeven because lasers are incredibly inefficient.  They're about 1% efficient.  So, were quite far away from the stage where the net energy output of the fuel is actually greater than taking into account all the inefficiencies of the lasers as well.  So, that's a really big step.  Should they reach breakeven and gain off a few, that's a really excellent stage because that shows that the method works.  However, in order to get a commercial power plant out of that, you need gains of between 30 and 100.  So, we need to do something extra in order to get to those gains. We also need to develop new lasers that are much more efficient than the lasers we have.  They don't exist yet.  And over maybe the next 6 or 7 years, there's a really concerted effort to build these new lasers as well.

Dave -   So, it strikes me that this is really quite a complicated exercise, sort of firing I guess, it got to be incredibly precisely orientated all these lasers and if you try and do this again and again, and again in essentially industrial process, how practical is it likely to be?

Kate -   Its kind of like throwing a tennis ball up and then trying to hit it with 192 other tennis ball. That technology is not particularly difficult really.  More to the point is, how do you inject an ultra cold pellet balistically without it heating up.  That's something we need to address. And also these new lasers as well.  So actually, out of all of the challenges, I think that's the least difficult one.

Ginny -   So, if you have to give me a best guess, how long do you think itll be before we have nuclear fusion energy powering our homes?

Kate -   I wouldn't want to put my finger in the air, but I mean, when you think about magnetic confinement fusion, you've got 2040 for a demo reactor.  And again, for inertial fusion, weve got to actually prove that it works and then weve got to show that we can get these high gains.  So, whatever comes after NIF, its still going to be a science project for all intents and purposes.  So, were decades away.

Ginny -   So, probably not the answer to our current energy needs right now then, unfortunately.

Kate -   Unfortunately, not but its got to be part of a patchwork of energy generating mechanisms that don't produce carbon.  Essentially, that's what were aiming for.  So, its the long term feature where energy does not produce carbon.


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