FST JOURNAL

• You need extremely high temperature, a density of particles and an eye on time to make fusion work.
• Inertial Confinement Fusion (ICF) is a system where fuel is compressed to a very high density at 10 hertz, until it self-ignites. 
• The National Ignition Facility in California achieved ignition for the first time on 5th December 2022.
• The UK have been world leaders for a long time in the science behind ICF and recently formed the UK Inertial Fusion Consortium which has produced a roadmap.

I want to talk about the science behind fusion and will start off by presenting the three knobs that we can twiddle to get fusion to work. So temperature is a non-negotiable, it needs to be hot. We then need to look at the density of the particles in the system, and the time in which you can confine those together to produce net energy. Imagine a system that has a moderate density of particles which you can keep together for a long period of time, or a very dense system of particles, which you keep together for a short period of time, but one that does that over and over again. It just so happens that the two main approaches to fusion fall into those categories. 

What is Inertial Confinement Fusion (ICF)?

You may have heard a lot about magnetically confined plasmas, which generally are a moderate density of particles kept together for a long time. On the other side of things, there is a system where fuel is compressed to a very high density until it self-ignites. This is like a diesel engine, but for nuclear fusion. If you do that at 10 hertz, you get Inertial Confinement Fusion, where you’re confining the fuel by its own inertia. This can be done with photons and it doesn't matter if it's lasers in the optical or it's X rays from Hohlraum. You radiate your ball bearing size pellet of deuterium and tritium and heat up the outer layer so that it expands very violently in a process called ablation. It’s a similar process that happens to your cornea during eye laser treatment, but much more violent! 

If you've got something ablating outwards very violently, by Newton's third law, the rest has to collapse inwards. Materials are compressed to about 1000 times solid density. Eventually this hot piston action will cause the temperature in the centre to become very large, so that you get what we call a hot spot. At this point, fusion occurs, alpha particles are produced there, things heat up further and more alpha particles are produced again. The result is a kind of fusion burn wave propagating through the full. This happens in a fraction of a second so you have to do that multiple times a second for something like a power station. That is what ICF is. 

The current fusion landscape

There is a massive facility built at the Lawrence Livermore National Laboratory in the Bay area of California called the National Ignition Facility (NIF). The clue is in the name. It was designed to work with Ignition, but although it is Ignition defined as the energy obtained from fusion is larger than the laser energy entering the system, it is not yet net energy or energy we “on the grid”

It is the largest laser system in the world, and frankly, as far as I'm concerned, the most beautiful laser system in the world. It's incredible. They filled it over 50 different diagnostics. Anyone who's ever done any kind of experiment knows that getting 50 instruments to work simultaneously is a miracle. They did not get ignition to begin with, there were lots of problems in terms of their predictive capability, and so forth, but after an incredibly beautiful, careful set of experimental and theoretical work, they managed to achieve it, which is incredibly exciting. I started this game in 2001, at an advanced inertial fusion scheme. So this is what I've been waiting for my whole career. They achieved this for the first time on 5th December 2022. They put in two and a bit mega joules of laser energy and got three and a bit out, which is a fantastic achievement. 

To put this into context, there's about a mega joule of energy in a four bar KitKat. I'm pretty sure you've never eaten a four bar KitKat in 10 nanoseconds (I know we've all given it a good go). That's the sheer power of this system and demonstration of this is robust. It's not just a one off. I hear on the underground grapevine, that we're now at around six mega joules of energy , which is very exciting but you didn't hear it from me.

On the global stage, the NIF is the only show in town that's capable of getting ignition, but there are lots of supporting facilities. There are lots of high rep rate low energy systems, which we do our bread and butter in. But (pictured) these are the ones that have been largely involved in inertial fusion energy. 

Where does the UK sit in the picture? 

We have a very well established, decades old community in the fusion space. It's a relatively modest sized community; six or seven universities and some national labs, the Atomic Weapons Establishment (AWE)  and First Light Fusion involved in these spaces.

We've been world leaders for a long time in the science. We've got high intensity lasers with Vulcan, Gemini and Orion. We are also world leading in targetry, capability, theory and computational modelling in the high energy density space. We definitely punch above our weight. There are also lots of scientists from the UK. Many who trained at Imperial College, ended up at Lawrence Livermore and have been deeply involved in the NIF programme with the ignition discovery. 

One of the things that our relatively modest community has done to try and give ourselves a bigger collective voice, is form the UK Inertial Fusion Consortium. It consists of about 90 members from the UK’s Central Laser Facility (CLF) and was established to try and foster a more joined up approach to foster collaboration, coordination, and to try and get a bit more of a collective voice for our community in the UK. Out of this, we have created a UK fusion roadmap, looking at the period from 2021 to 2035.

The Roadmap focuses on a number of different areas including the hardcore research side of things, funding, how to increase the funding going into the IP landscape, and facilities and technology. We have some of the best lasers in the world and some of the best technology so we are also looking at the UK strategy at large. 

But how do we grow the UK community? How do we grow equitably? Every decision must be made with a view to making our community more diverse, and more equitable. We have a deep relationship with UK AEA so it's really important to be joined up in the training of people who are entering the fusion space, and there's loads of overlap between the IFE (intertial fusion energy) community and the MCF (magnetically confined fusion) community. If you are interested in this roadmap or the consortium, there is more information below.

NIF ignition

https://www.nature.com/articles/d41586-023-04045-8

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.065102

 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.075001 

High Gain ICF schemes

https://royalsocietypublishing.org/doi/10.1098/rsta.2020.0028

 https://royalsocietypublishing.org/toc/rsta/2021/379/2189

UK Inertial Fusion Consortium 

https://www.inertial-fusion.co.uk