Culham Plasma Physics Summer School: Introduction

Hi, my name is Bailey. I've just finished my third year of an undergraduate physics programme at Royal Holloway, University of London, and I’m interested in plasma physics!

Unfortunately, Royal Holloway does not really cover any of this at the undergraduate level, and since I'm hoping to go on to do postgraduate research in the field, I feel I really should get a 'taster' before jumping in.

So this year I decided to attend the renowned Culham Plasma Physics Summer School!

The summer school is taught at the Culham Centre for Fusion Energy (CCFE), the UK’s national laboratory for fusion research. It is home to the famous donut-shaped star-making machine, the Joint European Torus (JET) experiment.

This machine is famous because in 1997 it produced the highest fusion yield that we have ever seen!
...but it took more heat energy to get it going than was extracted from it! So more research is needed...
The school is intended to give the student an introduction to the fundamentals of plasma physics together with an appreciation of how these are related to more specific applications (more on this later). It is therefore accessible to anyone who is at least in their final year of a physics-related undergraduate degree (i.e. me).

I’ll be staying in Oxford at the William Miller building with other students from the school for the duration of the trip, so I’ll be sure to explore this beautiful city, and also try to get to know the other students. I hear that together we represent at least 25 different countries!

William Miller building, 22 Dawson Street, Oxford
Anyway, lectures start tomorrow morning so I had better get some sleep!

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?

Nope!

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.
Source: UNSCEAR, NRPB
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: https://www.instagram.com/baiway/
All in all, a great first day! ;-)

Culham Plasma Physics Summer School: Day 2

Hello!

Today's lectures kicked off promptly with 'Plasma Kinetic Theory II', by Dr McMillan again. We looked at the Vlasov equation in more detail and from this obtained Langmuir waves and then Landau damping. I won't explain what these things are here - partly because I still need to read up on them to understand them fully, but also because I'm going to try to keep these posts considerably shorter than yesterday's.

Next we had a lecture on 'Classical Transport' by Dr Chippy Thyagaraja. This was brilliant.
Again, this lecture was quite maths-heavy, so I won't go into any detail.

Next we had a problem-solving session on Particle Dynamics.
This session was actually very well done; Dr Collin Roach - who gave the lecture - was around to help out, as well as several PhD students and post-docs to make sure we understood everything. They then gave us an answer sheet, and it turns out I didn't understand everything, but I think I do now!

Lastly we had a much more relaxed lecture on the 'History of Fusion' given by Mr Chris Warrick. This was a lovely note to end the day on, and I found out a lot of things that I never knew!
Unfortunately this evening hasn't involved any visits to pubs... Instead I went shopping for food only to discover that half of the food that I bought is going to go to waste because the kitchen doesn't have an oven! I also forgot to buy any cooking oil...
BUT I did discover that with enough of this stuff

...it's possible to cook without it! So long as you like that 'smoky' or... 'burnt' flavour...

After dinner I spent the rest of the evening going over today's lecture notes and preparing for tomorrow's kinetic theory problem class.

And that's about it!

See you tomorrow.

Culham Plasma Physics Summer School: Day 3

Day 3

Today was a really interesting day of lectures!

It started off with two sessions on Magnetohydrodynamics (MHD) by Prof Phillipa Browning
MHD is the study of the magnetic properties of electrically conducting fluids.
From Wikipedia: The fundamental concept behind MHD is that magnetic fields can induce currents in a moving conductive fluid, which in turn polarizes the fluid and reciprocally changes the magnetic field itself
In essence, it combines the Navier-Stokes equations of fluid mechanics and Maxwell's equations of electromagnetism to form the ideal MHD equations.

MHD describes large-scale phenomena well, such as the astrophysical phenomena. It also describes the behaviour of liquid metals, like the Earth's core and industrial processes. And it can often give useful information even when the conditions for validity are not strictly satisfied, e.g. tokamaks and the Earth's magnetosphere.

Prof Browning took us through a simple derivation of the MHD equations. Then introduced the magnetic Reynold's number and ideal MHD. She then talked us through Alfven's theorem - which effectively says that in a perfectly-conducting plasma, magnetic field lines are frozen into the plasma. This means that if the bulk of the plasma moves, the field lines must distort and move with it.
An example of this is the sun spinning on its axis:
I found this part pretty cool.

Next up we had a problem class on the plasma kinetics. This one actually went down quite well! You can see Daniel and I working on a problem in the mid-right of the photo below (I'm the pleb in the glasses that needs a haircut).

Finally we had a very interesting lecture from Prof Nick Braithwaite on low-temperature plasmas and their applications. I found this very interesting, in large part because I completely glazed over this entire area because I was so excited by the big flashy buzzwords that go alongside high-temperature plasma research. One of the coolest things that Prof Braithwaite showed us, I thought, was this remotely-controlled plasma experiment!

At the end of the day I went on a run along the river and then called it a day.

Culham Plasma Physics Summer School: Day 4 and 5

Hello! It's now the weekend and I didn't get round to writing much over the last two days, so here is a quick recap!

On Thursday morning we started with a lecture on Magnetic Confinement Fusion (MCF) from Dr William Morris - Chief Scientist at CCFE. I've already mentioned that this stuff is right up my street, so I won't go on too much about it. Needless to say, it was a very good lecture.
The next lecture was on Inertial Confinement Fusion (ICF) given by Dr Kate Lancaster of the University of York. ICF is a completely different idea to MCF - the idea is that the deuterium-tritium fuel mix is contained within a tiny pellet. This pellet is then compressed and heated using a high-intensity laser(s), which initiates fusion. Dr Kate Lancaster is a fantastic lecturer and made the subject incredibly interesting.
She also took a selfie at the end, but only really managed to get the front two rows!
After lunch we had a Poster Session that took us up until the end of the day. Some of the PhD students attending the summer school chose to bring along posters to explain their research to everyone. This is a great opportunity for them to get a chance to experience giving poster presentations - what makes up most of your time at a conference as a PhD student, and also gives people like me a chance to see what sort of things people are doing!
I had a good chat with as many of the PhD students as I could, and then we all voted for the student which we felt gave the best explanation of their work. I voted for Lia who had an excellent poster about her work on the interaction of the solar wind with the magnetospheres of planets in the solar system. It turns out she won!
Once school was done for the day, I quickly rushed off and got that much-needed haircut that I mentioned yesterday. Then I gathered some friends and we went for a quick meal at Nandos. We walked off dinner through Christ Church Meadow before joining the rest of the summer school students for a boat trip!

The views along the river were beautiful. We even passed through two locks - which is a first for me! All in all, a great evening full of drinks and good company!

The next day started with a lecture on Waves in Plasmas by Dr Chris Ham, who works in the theory and modelling department at CCFE. The lecture was delivered very well, and I actually feel I understood everything that was said, despite the 'mathsy' nature of it.
Next up was a lecture on Diagnostics by Dr Phil Morgan. This gave us all an overview of the kinds of probes that are used in real experiments to read out certain parameters.
And the final lecture of the week was on Heating and Current Drive by Dr Martin O'Brien. This answered many of the questions I had about how tokamaks actually work - Dr Martin O'Brien did an excellent job - especially considering the state of most of the students at the end of the week!
I'd love to say that I went out on a crazy night out to celebrate the end of the first week, but I honestly just went back to my room and slept! I was exhausted!

Anyway, it's now Saturday morning and I'm eager to post this so I can go and be a tourist around Oxford for the weekend!

Culham Plasma Physics Summer School: Day 6 and 7

Hello! The second week has begun, and so far it's been great!

The first lecture to bring us back into things was by Dr Ken McClements on Plasma Instabilities. I found this to be the most interesting/important lecture so far. Dr McClements focused mostly on MHD instabilities and gave us a good historical background so we could appreciate how the communities knowledge of instabilities has evolved with time. Understanding instabilities obviously plays a critical role in the development of MCF devices, as they set a hard limit for confinement.
Our next lecture was on Solar Physics and Space Weather by Prof Stefaan Poedts. This actually proved to be very interesting. Prof Poedts explained the importance of space weather predictions - dramatic solar events can have severe consequences on electrical equipment down on the surface of the Earth. In fact, in these more serious events it is important that electrical providers are informed so they can limit/shut down power supply to the grid to limit damage.

Next we had our final problem class on Waves in Plasmas, but after that came something far more interesting...
Our tour of JET!

I'd actually done the tour before, on a PhD Open Day, but this time I got to ask far more interesting questions! We also got to go into the Control Room, one of the perks of being shown around by one of the top engineers!

That pretty much concludes Day 6.

Unfortunately, I missed out on the tour of RAL on Day 7 because I was attending my girlfriend's graduation ceremony. How selfish of her!

Doesn't she look great though? (middle)



Culham Plasma Physics Summer School: Day 8, 9 and 10

Hello! You poor soul, you've made it through the whole of this awfully long blog!

On the morning of Day 8 we saw the return of Dr Thyagaraja, or Chippy, for a lecture on Plasma Transport. This was a follow-on from his earlier lecture on the more basic Classical Transport, and, well, the maths was a little more advanced too - to say the least. After celebrating with my girlfriend the night before, this lecture was a bit of a struggle! But I persevered!
Next up was a lecture on Plasma Turbulence, given by UK Atomic Energy Authority CEO Prof. Steve Cowley. This was another very interesting lecture that didn't dwell too much on complicated maths, but focused much more on understanding key concepts - something my hangover and I really appreciated
The final lecture of the day was on Plasma Wall Interactions given by Dr Fulvio Militello. This wasn't so much on the appreciable engineering problem that is to create sufficiently resilient materials to withstand the hostile conditions inside future tokamaks (i.e. ITER, DEMO), but was focused more towards the effect these interactions have on the stability of the plasma itself. This wasn't something that I had thought about at all, and I found it very interesting. I found myself really looking forward to Dr Militello's next lecture the following morning!

But first came the tour of MAST! I was particularly excited for this because I had not been shown around MAST on my previous visit - so this was all new. It was also very interesting because MAST is currently undergoing an upgrade, so I got to get up and close to the vacuum vessel itself! Here's a picture I managed to snap:

MAST
And that about wraps up Day 8.

The highlights of Day 9 were certainly the first two lectures. It started off with another lecture from Dr Militello, but this time titled Edge Physics of Tokamak Plasmas. This was a very interesting lecture on the rich physics at the edge and the scrape of layer (SOL). This, together with the lecture on instabilities, have made me want to do much further reading into these fields. I can see myself continuing to do research in these areas.
Next up was a lecture on Dusty Plasmas from Dr Michael Coppins at Imperial. At first I didn't expect this lecture to be very interesting at all, but it turns out Dr Coppins is a world-leading expert in this field - and boy, was I wrong! A dusty plasma is a plasma that has millimeter to nanometer-sized particles suspended in it. The reason that dusty plasmas are interesting is that the presence of these additional particles alters the charged particle equilibrium leading to different phenomena. Electrostatic coupling between these particles can vary over a wide range, leading to weakly coupled (gaseous - more similar to what we're used to) to strongly-coupled crystalline plasmas. For example, below is an experiment done in zero-gravity onboard the International Space Station (ISS):
Example of self-organisation in crystalline plasmas
Dusty plasmas are interesting because they provide a non-Hamiltonian (i.e. irreversible) system of particles as a means of studying the fundamental physics of self-organisation, pattern formation, phase transitions, and scaling (e.g. could this be used to study webs of dark matter?).

After another two lectures, we sadly came to the end of our penultimate day at Culham. However, we were in store for a treat - the Banquet at St Edmund's Hall!

I was lucky enough to sit across from Professor Roger Cashmore, Chairman of the UK Atomic Energy Authority (the man who introduced the summer school). Here's a screenshot of the highlights of his career from the 'Key Staff' page on CCFE's website:
So as I'm sure you can imagine - he had a few interesting stories to tell! Of course, it was lovely to have a final meal with my peers too. We all exchanged stories over good food and wine.
After the banquet, we had a few drinks in the Hall bar. I was lucky enough to have a chat with Prof. Steve Cowley, CEO of the UK Atomic Energy Authority. Let's hope it helps me secure a future PhD placement with him!
When the Hall bar closed, we moved on to another bar (I honestly don't remember where it was or what it was called), and on the way we got this picture!

Now for the last day... :(

We had a lecture from Dr Stuart Mangles on Laser Wakefield Acceleration, which is a proposed method of accelerating particles using the wake from an electric plasma wave. See the figure below to get an idea for the physics:
Source: Wikipedia
The principle was first demonstrated experimentally in 1988, but the field has recently seen many advancements and is looking very promising! 

Finally, we had a very interesting lecture from Dr Jakob Svensson on Connecting Theory with Experiment. This was essentially a deep look at a more 'philosophical' understanding of Bayesian statistics - something which is often overlooked. I really enjoyed the approach of this lecture. Dr Svensson's first slide was this:

The point being that in science we often try to infer quite a lot of detail just from some numbers of some screens. How exactly do we do this?
In general the forward problem is quite an easy one to solve, i.e. measuring the temperature of some conducting wire. The inverse problem is far more difficult to solve, and is often the one that we are most interested in - going from data to understanding the underlying physics. Dr Svensson explained it like this:


And the rest of the lecture followed in a similar style - nothing too complicated, but he raised some important 'philosophical' points that really made me think. This all ties in very well with a course I'm taking next term called Statistical Data Analysis - so I'm hoping to learn more about Bayesian probability theory there. All in all, this was a great way to finish the course.

After the final lecture, we all got the coach back to Oxford train station and from there people went their separate ways! We all promised to keep in contact with each other - and maybe one day we'll even be working with each other!

So a big thanks to the Culham Plasma Physics Summer School - everyone who taught, organised and attended it. I had an excellent time. And a big thanks to The Ogden Trust for funding me on this trip.