Culham Plasma Physics Summer School: Day 1

Hi! Me again.

The first day started with breakfast with all the other students. I got to meet Daniel from Barcelona, Jonah from Tennessee, Manuel from Columbia, Juuso from Finland and Mustafa from... Bedfordshire.

When we were all finished, the coach picked us all up from outside the building and drove us for around 30 minutes to the Culham Science Centre.
The Culham Science Centre not only home to the CCFE,
but also to lots of other businesses specialising in fields such as
forensics, cancer diagnostics, and many others!
When we arrived, we were shown to the lecture theatre (where we'd be spending the VAST majority of our time) and received a warm welcome from Prof Roger Cashmore - Chairman of the UK Atomic Energy Authority.
Next, we received a sort of warm-up lecture on fusion and its role in the future energy market. The lecture was given by Dr David Ward, who has done both theoretical and experimental work in the field, but now looks at the socio-economic issues that a demonstration fusion power plant (DEMO) would bring.
Dr Ward started by emphasising the growing energy demands of the world, particularly by China.

N.B. Mtoe refers to a megatoe; toe meaning tonne of oil equivalent.
Source: BP
More interestingly, though, he pointed out that the predicted energy demand growth is dominated by a demand from developing countries. Note that China is included as a developing country, because its per capita income is significantly less than advanced countries.
FSU - Former Soviet Union
CEE - Central and Eastern European
OECD - Organisation for Economic Co-operation and Development

N.B. This assumes no increase in OECD energy consumption on the basis that research
 into efficiency improvement balances growth.
Then, of course, he talked about the paradox of the need to meet increasing energy demands yet reduce CO2 emissions. Here's another graph!

Source: Socolow and Pacala (2006)
From 1956 to 2006, the wobbly part of the graph above shows real data on the increasing amount of carbon emitted per year. The authors of the article assumed a linear increase in carbon emissions from 2006 onwards and compared two different futures 50 years on (it should be noted that they only included existing technologies in the study). 
Dr Ward pointed out that that flat path leads to a CO2 target of ~500 ppm, but it is a challenging target to meet. It would amount to the equivalent of increasing fission capacity by a factor of 15 (not an easy thing to do). Further decreasing emissions in 2056 would be extremely difficult. The different wedges in the graph above describe progressively more realistic targets, but lead to extreme CO2 concentrations of ~850 ppm (NOT GOOD!). 

It is clear that CO2 emissions need to plateau and then decline in order to keep atmospheric concentrations below ~550ppm, but an increasing energy demand makes this incredibly difficult. 
Source: IPCC
Decoupling energy and CO2 will require dramatic changes to existing energy systems. 

...which is where FUSION comes in!

Nuclear fusion is a high-energy process in which two light nuclei, for instance deuterium and tritium (hydrogen isotopes), collide to form a heavier nucleus. The energy yield of this reaction is very high.
A deuterium-tritium (D-T) reaction
Okay, great. Energy crisis fix'd.

But how do we get this deuterium and tritium to meet the world's energy demands? Well, it's actually quite easy! Deuterium is a relatively abundant isotope of hydrogen - having a natural abundance in the Earth's oceans of around one in every 6430 atoms of hydrogen. It is predicted that there is enough deuterium already available for billions of years of energy supply.
The limiting factor is tritium. It is not nearly as naturally abundant as deuterium owing to the fact that it is radioactive and has a relatively short half-life of 12.32 years. Only trace amounts found of tritium can be found naturally on Earth, and these are due to the interaction of cosmic rays with the atmosphere.
It is therefore necessary to produce tritium artificially. This is done by the neutron bombardment of lithium-6.
Now, this is good because lithium is incredibly abundant! See the graph below of the abundance of elements in the Earth's upper crust (where we can dig for stuff)
Source: Lithium - Wikipedia
Fun fact from Dr Ward: the lithium from 1 laptop battery can be used to produce enough tritium to provide your lifetime electricity needs! (~240,000 kWh). It is predicted that there are sufficient lithium reserves for thousands to millions of years.

The conclusion to draw from this is that fuel reserves are enormous and are not in any way an issue.

Okay, so why isn't hasn't fusion power become a reality yet? Is it because of emissions? Is fusion super dangerous?


Below is a plot showing the radiological hazards of various energy sources. The food column is indicative of background effects, e.g. potassium-40 in bananas etc. and not directly comparable to the others. Improved windows reduce the ventilation of indoor radon. You can see that fusion poses little threat when compared to other things we readily accept.
The manSv is a measure of collective dose, it could correspond to 1000 people
receiving a dose of 1 mSv, or  10 people receiving a dose of 100 mSv. 

Conventional energy hazards are enormously greater than fusion hazards. Moreover, because radiological hazard from fusion materials decays rapidly, with a half-life of around 10 years, meaning that waste is no where near as much of an issue as it is with fission.

Now, Dr Ward raised an interesting point on waste and by-products that I would have never thought of, and I think its worth mentioning...
It is well known that carbon-14 is produced naturally in the atmosphere by the cosmic ray bombardment of nitrogen. It therefore exists naturally and is present in all organic lifeforms - this forms the basis of radiocarbon dating. Now, in a nuclear fusion power plant the same thing happens but with much larger fluxes - so lots of carbon-14 is produced. This is bad for several reasons:

  1. If ingested, carbon-14 can be very dangerous owing to its long half-life.
  2. It could potentially cause issues with radiocarbon dating!
Keeping carbon-14 production well below natural levels requires nitrogen concentrations of 100 ppm or lower. SS-316 (fancy stainless steel), which is planned for use in ITER, has a nitrogen concentration of ~600 ppm. Engineers will need to move away from this for DEMO reactors (see here) where the neutron energies and fluxes will be far greater, and will need to look at reduced activation materials (RAFM).

I mention this because it highlights the fact that there are many different things that researchers must consider when designing these machines.

The final potential issue that Dr Ward highlighted was the big one... what if an ACCIDENT occurred!? (he was quite reassuring, actually!)
The main hazard in an accident would be tritium. In a small internal accident, the maximum release would be a few 10's of grammes. The resulting dosage to the local population would be, in the worst case, too low for an evacuation to be considered. In a much larger external accident, say, an enormous earthquake, the releases could be much higher but in reality the consequences of the event itself would be far more serious than any releases from the plant.

So from what Dr Ward has told us, fusion really does sound like a good thing! So let's talk about money.

Up until now, large-scale machines designed for fusion and plasma physics research have proved to be very expensive, but this is expected because, as with any emerging field, the 'groundwork' must be done first. Take a look at the price of photovoltaic cells, for instance:

A plot of the price per watt of photovoltaic cells over time
The global capacity (actual power produced annually) of photovoltaic cells
This tells us that, at least in the case of photovoltaic cells, a doubling in production reduces the price by around 15%. And it is true to say that this process of 'technological learning' is true for many other things too! Including building fusion reactors!
Source: Dr Ward's PowerPoint (I do not have the source, sorry!)

Note that some of these data points represent the power that a
non-DT device would produce if it were to use DT.
Gigawatt-scale devices are projected to be in the few dollars per watt range. To compare, the construction costs of a coal power plant is around $2.60 per watt. The Three Gorges Dam is reported to have cost around $26 billion, giving around $1 per watt. Large wind turbines cost around $2 per watt. So these devices are expected to be reasonably priced! And future R&D work will only reduce costs...

So what might the future energy market look like? And how can fusion contribute? 
Well, it is clear already that it is necessary to reduce fossil fuel consumption in order to reduce carbon emissions. In this low carbon future, fission and renewables can provide the growth needed for the next 50 years or so. After that, conventional nuclear systems will need to be replaced by advanced nuclear systems (breeders, fusion) in order to meet the ever-increasing demands.
Source: Dr Ward's PowerPoint (again, no source!)
An alternate future may be that fission is constrained due to public acceptance on the basis of safety concerns, what to do with the radioactive waste, and fear of proliferation. Or it could be that fission, due to its intermittency, is unable to provide as much growth as is projected. This may mean that other sources, like fusion, are needed much earlier. 
But what if fission's rejection affects the public's opinion of fusion? Would it be more or less likely to take off? These are very serious questions that will need to be studied in detail over the coming years. 

Regardless of which future becomes a reality, it is clear that the introduction of new energy sources is essential. Fusion is an excellent candidate for large-scale deployment globally due to its enormous fuel reserve and favourable safety and environmental characteristics. But is enough being done? 

Source: IEA, BP
Public Sector Energy R&D is a negligible fraction of the world energy spend, and fusion is just a small part of that negligible fraction. 

Dr Ward left us with these conclusions:

  • World energy consumption is likely to more than double even if OECD countries cap their energy consumption
  • Continuing business as usual implies a large increase in CO2 emissions and other pollutants globally 
  • There is an enormous energy market for low-carbon, low-pollution energy sources, like fusion
  • Fusion has large benefits in terms of fuel resources, environmental impact, safety and waste materials
  • Scientists must focus on demonstrating fusion as a power source, with devices like ITER having a yield of 10 (ten times as much power out as you put in). The benefits listed must be optimised, and at the same time costs must be reasonable
  • The world is not putting enough money into fusion or energy R&D in general if we are to achieve the transformation in energy markets that is needed.
Okay, done! 
Sorry for going into such a silly amount of detail, but I feel this talk provided a great sense of motivation for the rest of the summer school. I felt it would be a good read for anyone reading this blog that might not have looked at plasma physics or fusion in a great amount of detail. 

Now for a brief summary of the rest of the day:
The next lecture was by Dr Colin Roach and it was titled 'Particle Dynamics'. 

This lecture was a nice introduction into the basics of plasma physics. Particle dynamics is as the name suggests - a microscopic treatment looking at the dynamics of individual particles in the plasma. We started with the fundamental stuff; Debye shielding, quasineutrality, and an introduction to collective behaviour (waves). Then we looked at different kinds of particle drifts, which arise from having charged particles in an electric and magnetic field. Finally we looked at collisions and collisional transport.

I found the lecture quite easy to follow (it was supposed to be a gentle introduction, after all), but I did find myself wanting a little bit more detail. I decided that in the coming weeks I'm going to pay a visit to CCFE's library to choose a textbook to buy.

The final two lectures were given by Dr Ben McMillan and were on Plasma Kinetic Theory. Kinetic theory describes the plasma using a statistical treatment of many particles, and keeps information about the position and velocities of these particles. It fits somewhere between the microscopic description of individual particles (the previous lecture) and fluid dynamics (MHD) which only deals with averages over all particle velocities.

Dr McMillan started with writing down an expression for the Lorentz force, and then introduced a probability density N(x, v). He then explained that the electric and magnetic fields are then self-consistently determined from the particles themselves via Maxwell's equations. This let to the Klimontovich Equation. However, this equation turns out to be no easier to solve than the N-body problem (not easy). So we took an ensemble average, which gives the distribution function (this turns out to be very important), ignored the effects of collisions, and obtained the Vlasov equation. This is a differential equation describing the time evolution of the distribution function of a plasma consisting of charge particles interacting over long-ranges via the Coulomb interaction. Dr McMillan said that this was a good place to stop for the day, and that we would continue with this tomorrow!

So that was the first day of lectures! After that we had a welcome dinner at St Edmund Hall, which interestingly has a claim to be "the oldest academical society for the education of undergraduates in any university, but wasn't granted college status until 1957!
Source: Wikipedia
St Edmund Hall's courtyard
The dinner was lovely! It was nice also very nice to get to know some of the other students better. After dinner we decided that a trip to the pub was in order, and we ended up stumbling into the Turd Tavern, which is apparently one of the oldest pubs in Oxford!
Shameless plug:
All in all, a great first day! ;-)