Materials research - Small Balls and Pretty Patterns

By Alex Cackett and Jim Hickey

As we all know, magnetic confinement fusion is around the next corner and we’re just dotting the i’s and crossing the t’s. Such a statement would be true if we wanted to build a very expensive power source that would disintegrate in a few years. This highlights a vital area of fusion research, developing materials that can withstand the harsh environment plasmas impose on their containers. Culham Centre for Fusion Energy (CCFE) is currently a large component of a resurgence of nuclear materials research in the UK, known as the National Nuclear Users Facility (NNUF) which aims to, in a nutshell, figure out the following:
 
     1. How long can we keep the current fleet of nuclear fission plants running?
     2. How will the recently developed materials behave in the new reactors currently under construction? (e.g. at Hinkley Point)
     3. Can we solve some of the materials conundrums for future fusion power plants so that they are economical and last longer?
 
The Materials Research Laboratory (MRL) at CCFE is a baby lab with the primary aim of looking at materials on the small-scale. It contains some very cool pieces of kit with even cooler names: a nanoindenter, a Focused Ion Beam (FIB) and a Scanning Electron Microscope (SEM). More on these bad boys later but in short, the MRL is a precursor to the Materials Research Facility (MRF), which is currently being built here at Culham. The major difference between the two is that the MRF will be able to do everything we’re currently doing in the MRL, and more, on mildly radioactive materials (think lamb bhuna spicy).


Focused ion beam beast in the MRL

Both nuclear fission and fusion reactions we currently use, or would like to use for power generation in the future, produce neutrons. These neutrons can be thought of as sub-atomic snooker balls (great band name) that simply smash into the atoms that form the components of your reactor. This can cause all sorts of phenomena including knocking atoms out of their usual locations, degrading the mechanical properties of the material and causing further nuclear reactions that can cause radioactivity.
We use all sorts of different materials in a nuclear reactor to satisfy different roles. For obvious reasons, certain metals and alloys (e.g. steels, zirconium, CuCrZr) and some of his/her mates are used for lots of structural applications. They are usually stiff, strong and retain these properties reasonably well as they are bombarded with neutrons. We want to understand exactly what happens to these mechanical properties as their exciting existence proceeds in a reactor. This has historically been done by either pulling apart quite large lumps of irradiated material to investigate the change in their properties or by simply replacing parts once they have exceeded very conservative lifetime expectancies.

Cherenkov radiation in a small fission test reactor in the USA. Although it looks very lovely, it is the result of high energy particles being emitted from nuclear reactions within the core.

 
 Small balls - why size matters

Our graduate project is based on developing a technique, based on a process called nanoindentation, to extract the mechanical properties of very small (micron-scale) volumes of materials for nuclear applications. Nanoindentation is basically a glorified word for prodding a little diamond tip into the surface of a material and measuring the response. Tips come in different geometries and we are using tips of a spherical shape. Spheres are great as they elastically deform a material before permanently deforming it compared to tips with a sharp end (think knifey-spooney). This is very important as we can therefore plot stress-strain curves, a sort of fingerprint of the mechanical properties of a sample. Nanoindentation is also semi non-destructive in that you leave a tiny little pimple in your sample but you don’t completely destroy it. This has obvious benefits if you want to figure out how your expensive reactor component is doing throughout its service life.
Size really does matter here and researchers in the field have always been trying to reduce the volume of test specimens. The smaller a radioactive test sample, the easier it will be to handle. Also, most techniques currently used to irradiate/mimic irradiation in materials only manage to do this on a very small volume of material anyway, usually by firing ions at the material. As mentioned above, small-scale testing will also not destroy your very expensive reactor component and you don’t have to shut down your reactor for a long time to get at it, keeping the money gods happy. The issue is though, the smaller you go, the less representative the properties are compared to bulk components. This is called the size effect and is one of the banes of a materials scientist life or a happy challenge, depending on what you’re researching/ approach to life is.  Our challenge is to characterise the size effect for different materials by using different size spherical tips, ranging from 1 to 150 micrometre in radius. This way the strength of the material can be plotted against tip size to characterise the size effect.
 
TKD - what, why and how?
 
Transmission Kikuchi Diffraction (TKD) is a recently developed technique that’s currently being explored in the MRL. It can be used to gather crystallographic information (atomic configuration) using only tiny volumes of material to do so, but that’s not the only reason it’s attractive to material scientists; it can also be performed inside the SEM and is capable of achieving spatial resolutions as small as 2 nanometres (nm), which is an order of magnitude improvement on the next best thing - electron backscatter diffraction (EBSD). Traditionally, high resolution imaging could only be obtained using transmission electron microscopes (TEMs) which are tricky to use and bloomin’ expensive. Now with TKD, all you need is a SEM with an EBSD detector (essentially a CCD camera and phosphor screen) and you’re good to go!
 
A lot of materials have some form of crystal structure, which means their constituent atoms are regularly arranged in a repeating 3D pattern that forms a lattice. When electrons are fired at a material some of them are diffracted by the planes of atoms and can be collected by a detector forming patterns, like the one seen in the figure below, called Kikuchi patterns. Each Kikuchi pattern is characteristic of the sample material and crystal orientation, so by scanning the electron beam over the whole material surface it’s possible to form a map of crystallographic information. This is essentially how EBSD works, but TKD is a slight variation on this method. Rather than collecting the backscattered electrons bouncing off the sample surface, instead it is the electrons that have been transmitted through the material that are used.

Kikuchi pattern of single crystal Si with orientation <001> normal to the sample surface



As you can probably imagine, for this to be possible the samples have to be extremely thin, ~200 nm (1/50th of the longest dimension of a human blood cell!). This is where the focused ion beam comes in handy. Gallium ions are used to bombard the bulk specimen (think sand-blaster but on a much, much smaller scale) and mill away material to form a standing wafer in the surface. The wafer can then be stuck on to the end of a precisely controlled needle using platinum ‘glue’ and moved to a small holder where it’s mounted and ready for thinning. Thinning is also performed using gallium ions, but at a much lower velocity, so the ions are not implanted into the wafer (this can damage the material and ruin the Kikuchi patterns). With some precision milling, and more than a little patience, the wafer can eventually be thinned down to a skinny 200 nm. It’s then ready to be placed in the SEM for TKD analysis. The results of all this hard work can be seen here - a rainbow-coloured, first of its kind, strain map around a spherical indentation, tah-dah! With the MRF opening next year there is the possibility of using this technique on irradiated materials, so stay tuned for a follow-up blog post on that.


Strain mapping around a spherical indentation placed at the edge of a grain boundary


More information on the NNUF and the MRL can be found at the following websites:
http://www.nnuf.ac.uk
http://www.ccfe.ac.uk/mrl.aspx

KIT Summer School Factfile

From our experience at the KIT Summer School (see the full blog post here) we compiled a list of interesting facts about FUSION that we learnt, and also facts about GERMANY.

 Fusion Factfile 

1. The TF coils in ITER will store over 40GJ of magnetic energy! That’s 15 times the kinetic energy we store in our massive flywheels at JET. 

2. I was surprised to learn that the Lorentz force generated by the maximum current planned for one of ITER’s TF coils would cause them to collapse if they were self-supported. 

3. The assembly tolerances for the ITER vessel and magnets are phenomenally tight. This will be an incredible feat of engineering when they achieve it.

4. Stellarators look freakin’ awesome 

5. The ITER toroidal field coils will contain 150,000km of superconducting strands – enough to stretch over 3 times around the circumference of the earth.   

6. Super conductivity is really clever! But making superconducting magnets seems painfully difficult. High temperature super conducting materials are going to be really important for future fusion devices. 

7. KIT have the largest tritium lab in Europe and are the only lab capable of conducting tritium research for ITER. ITER will weigh 27,000 tonnes (3 times Eifel Tower).
 

    8. Cryopumps don’t actually “pump” anything! They work by condensing all the gas molecules onto a very cold surface, which periodically has to be regenerated by heating it up  - just like your freezer! This makes long-term continuous operation a big challenge for DEMO.

9. ITER will be testing out 6 different breeder blanket concepts to see which one works best.

10. The Tore Supra tokamak has an 8-metre long ‘Articulated Inspection Arm’ which is fully integrated in the tokamak vacuum. An inspection can be done after every pulse without interrupting the vacuum! 

 

Germany/KIT Factfile

 

    1. Karlsruhe’s beautiful palace gardens are open to the public every day; for free! 

    2. If you are not used to Steins, be careful not to drink them like a pint…  

    3. There’s a free shuttle bus between KIT south and north campus, which is very convenient! 

    4. German cycle commuting is awesome! Much better infrastructure for cycling, and European style commuter cycles (rather than sport oriented cycles) are actually a lot better than I had expected – really easy for commuting with.

  

5. Mike from Mike’s Bikes: what a dude. He will rent you a bicycle for around 10 €/day. Do it. Cycling through the forest, along beautifully smooth cycle paths to and from the KIT campus is sweet. Beats the bus.  

6. Karlsruhe was dreamt up by Charles III William in 1700s during a nap – he designed the city to look like the sun radiating from the palace in the east. 

7. It’s easy to buy really good non-alcoholic wheat beer and non-alcoholic cocktails at almost all restaurants and bars. 

8. Don’t forget to ask for a receipt at the KIT canteen 

9. When you’re packing to go to the KIT summer school leave room for about 2kg of lecture notes and 2 or 3 bottles of souvenir wine. 

10. Three-course meals every night take their toll. Germany is very good at providing individual receipts. 

11. The free KIT wi-fi is also available at the Studentzentrum on the south campus (i.e. where the shuttle bus stops), and in the grounds in front of the palace in the city centre (Karlsruhe Schloss) 

12. “Europabad” is well worth a visit. 

13. Sometimes German transport isn’t on time!

KIT summer school 2014

This year 74 people new to Fusion Research went to the Karlsruhe Institute of Technology (KIT) in Germany for the yearly 2-week holiday…ahem... I mean Summer School on Fusion Technology. There were people there from all over Europe, but also people from as far away as India. There were 17 of us going from Culham, 10 graduates, 1 PhD student, and 6 experienced engineers/physicists (semi-) new to the field of Fusion. 

Image courtesy of KIT

It was a chance to learn some basics about plasma physics, the politics and future of fusion, technology used in the industry and other tokamaks across the world. It was also a chance for eating good food, drinking good beer and general partying (ahem…I mean networking). We had some very good lectures and tours at KIT, but I’m not going to bore you with details of everything, so I’ll just give you some highlights. 

Our first lecture of the school was CCFE’s very own David Ward, a pioneer for the role of fusion in future energy. He reminded us of the massive problems the world faces with respect to energy, and how little is being spent on new energy research.  Personally I was struck by how often people doing research into Fusion claim that too much is being spent on other renewables and not enough on Fusion, and vice versa- people doing research into solar or wind power often have the opinion that too much is being spent on Fusion. The reality seems to be that nowhere near enough money is being spent on any of it, and instead of attacking each other, we should be advertising this fact. Anyway enough of that because David has inspired a new blog post on this subject- coming soon.

All of this learning was pretty exhausting, so we decided to let off some steam by going to the local water park ‘Europabad’. There were some awesome slides, including one where you stand in a pod, press ‘go’, a countdown begins and then the floor disappears and you are *dropped* vertically down a slide. It was great. There is a random YouTube video here https://www.youtube.com/watch?v=0PqooMXBr1Q. 

Back to school: after some introductory plasma physics, we headed straight for the deep end, and got up to speed on the latest on plasma heating and diagnostics, breeder blanket designs, divertors and neutronics. In between lectures we had some great tours of the KIT site. In the first week we went to the Test Blanket Module (TBM) facilities and learned about the research they are doing for ITER. We also saw the HELOKA facility, which is designed for testing various components for nuclear fusion facilities including the ITER test blanket modules and divertor modules, and the High Flux Test Modules for IFMIF (International Fusion Material Irradiation Facility). Here are some of the Culham Engineers next to the big vacuum vessel they use.

We were staying in the Jugendherberge (Youth Hostel ) which was very close to the city centre (and the huge beautiful park). However, this meant that there was a 10km journey to the KIT north campus every day. There was a free bus which was great, but a few of us decided to make use of the amazing bicycle paths through the forest all the way to the campus and hired bikes for the duration of the school. Here is a selfie Jon C took while enjoying a nice pootle through the forest. Great idea until Germany decided to rain (pour) on us. We got soaked and Jon K got a puncture and had to walk 6km in the rain. A large Weissbier was required after that. 

At the weekend the KIT organisers had arranged for us to go on an excursion to a nice town called Speyer. I think they knew exactly what kind of people we were because after eating the biggest pretzels you’ve even seen, and looking at the nice cathedral with pretzel decorations (they like their pretzels), we went to the Technic Museum Speyer. They had a “large collection of aircraft, classic cars, locomotives and fire engines, some of the highlights are an original BURAN spaceshuttle, the largest space flight exhibition in Europe, a Boeing 747 Jumbo Jet, the submarine U9, a former German Navy submarine and a gigantic Ukrainian Antonov AN-22 cargo plane.”  This, plus 70 engineering enthusiasts resulted in the most excited group of geeks you can imagine. When Jon saw the moon-rock we thought he might implode, and we had to drag Greggles out of the submarine so we could go on the slide from the Jumbo jet.  If the day wasn’t good enough already, we then we sent off to taste some wine from the Rhine valley, and had a large buffet dinner. An epic day out was had by all.

The following week we were taught about tritium handling, vacuum pumping, superconducting magnets and remote handling. We learnt about various tokamaks around the world – Tore Supra (France), JT-60SA (Japan), ASDEX (Germany), Wendelstein 7-X (stellerator, Germany) and ITER.  These were interspersed with nice sunny evenings in the park (with a 1.30 Euro beer from the student bar), some slacklining and juggling and Chinese takeaway. Not forgetting Scruffys the Irish bar which specialised in live music and Jägermeister.

Another tour around KIT gave us the opportunity to see TOSKA, where they are doing tests on scaled-down versions of the ITER superconducting magnets, the cryogenic test facility (CryoMaK) and the tritium lab. We also got to have a go on the remote handling arms, and to play with liquid nitrogen using a glove box. 

On our final day we welcomed CCFE’s Nick Balshaw and Liz Surrey who spoke to us about JET and DEMO respectively - two fantastic talks to finish the school with (unbiased of course).  We went away feeling enthused and happy and at least 5 pounds heavier.

I asked attendees to give me two facts that they took away from our experience in Germany, one about fusion and one about Germany. If you’re thinking of attending KIT next year these will be useful! Link here.

Graduate intake 2014!

It’s October (we’re all wondering where the summer went??), but this means new Graduates destined for a fun two years and great things beyond. Here is a blog piece with cheesy picture to welcome them to Culham and find out a bit more about them.

I asked them to answer some sensible as well as silly questions, and got a variety of answers especially for the favourite pudding one. I think it says a lot about a person. Here are their answers in order of appearance in the photo in front of JET...

Victor Agudo Polytechnical University of Madrid (UPM), Aeronautical Engineering specializing in jet engines.

Department : Remote Handling (ITER) 

Favourite Pudding: Cheesecake without doubt. 

If you could be an animal what would you be: I would probably go for a quokka, looks like they are pretty happy.

Hopes for the graduate scheme: Apart from a valuable professional experience, I would like to get a bunch of good friends, great times and maybe, if I cross the right gamma ray, some sort of super powers or at least a cool glowing halo.

Alex Davies, University of Surrey (Guildford), Physics. I have spent the last year working in an Indian engineering consultancy called HCL. . Before I came here I always wanted to be a teacher, and at some point in my life I think I will do that, just not yet.
Initial Department : Tritium Group, Water Detritiation System (WDS) 
Important information: Can be bribed with chocolate   

Simon Kirk University of Cambridge, MEng Mechanical Engineering, PhD Experimental Physics 
Initial Department : Central Engineering 
Favourite Pudding: Chocolate and Pear Trifle 
If you could be an animal what would you be: Sea Lion 
Hopes for the graduate scheme: Learn about all the different parts of CCFE and what they do. 
Other interests: Rowing

Samual Ha, Imperial College London, Mechanical Engineering with Nuclear. 
Department : Remote Handling 
Favourite Pudding: Brownies 
If you could be an animal what would you be: White Crane 
Hopes for the graduate scheme: I’m hoping to get experience and a good time out of the graduate programme.
Other Interests:  My interests are few and far between, generally including exploring the great outdoors and/or exercising.

Bruce Edwards, University of Bath, Masters in Aerospace Engineering. Industrial placement at Siemens Magnet Technology (MRI Magnets), Cryostat dept. 
Initial Department : Remote Handling (DEMO & JET) 
Favourite Pudding: It depends whether you mean pudding in the traditional British sense or a general dessert. As bake-off enthusiasts will know this is a non-trivial distinction. If it is the former I may be inclined to opt for steak and kidney although Yorkshire would be a close second. If the latter was the intended meaning then perhaps a decadent chocolate mousse. 
If you could be an animal what would you be A blobfish (to improve my appearance)… or a golden eagle.

 
Hopes for the graduate scheme: I hope the opportunity to get involved in a variety of projects and accumulate a good cross-section of technical skills and competencies. Variety is the spice of life. 
Other Interests: Other interests include cycling (which I enjoy boring people with), climbing, running, slacklining, ale and whisky. Also I have a homemade 3D printer (RepRap). 

Jake Stephens University of Bath, Electrical Power Engineering 

Initial Department : JET Power Supplies, Ohmic Heating 
Favourite Pudding: Easier to list those puddings which are not a favourite: “…” 

If you could be an animal what would you be: Something Canine, doesn’t really matter what, they all seem to be mostly excited about everything. Seems good to me except fireworks and thunder would apparently lose all appeal. 
Hopes for the graduate scheme: 
Twelve Drummers Drumming
Eleven Pipers Piping...
Actually to finish it with the same smile as this guy

knowing there are some awesome people and possibilities ahead.

James Andrews The University of Manchester, BEng Mechatronic Engineering 
Initial Department : Remote Handling 
Favourite Pudding: Banoffee or carrot cake 
If you could be an animal what would you be: Dolphin 
Hopes for the graduate scheme: Learn lots about engineering and science and contribute towards providing sustainable energy for our future as a race.

Here is a sensible photo of them in front of JET (in case you genuinely want to see what they look like!) 

A Tale of Two Tokamaks - Post the First

By James Edwards

See Post the Second here.

It was the best of times, it was the worst of times. It was 1973. Design work officially began on the Joint European Torus (JET). Several of the pioneers of the first fusion devices had already been thinking about how to make much larger tokamaks than any that had existed before, and now they’d been given the permission to go ahead from the Council of the European Community.
 

The JET design team in 1977.

Design work for JET, headed by Paul-Henri Rebut, started off well and progress was quick, but there came to be disputes over where to build the machine. The two contenders to host the international experiment were Germany, which would host it at Garching, and the UK, which would host it at Culham. Neither country was willing to concede, so over the years following 1973, the design team became dissatisfied with the project’s political procrastination.

However, in October of 1977, a Lufthansa aeroplane had been hijacked by members of the Baader-Meinhof gang and Palestine Liberation Organisation. The GSG 9 (part of Germany’s police force) used stun grenades provided by the UK’s SAS to successfully rescue the passengers while the plane was at Mogadishu, in Somalia. After this event, it’s often said that West Germany and the UK came to an unofficial agreement that JET would be built at Culham. About a week after the incident, construction on machine components started.

The JET Torus Hall being built in 1980.

Final design work progressed well with the renewed vigour of the team, and on the 18^th of May 1979, work started on constructing the JET buildings and infrastructure at Culham. As some of the machining for components had been started earlier than this, it meant that the initial functional tokamak was completed by 1983 on time and on budget and by 25^th of June of that year, the first ever JET plasma popped into being. Allegedly, many bottles of champagne were quaffed in celebration.

First plasma in the (very) bare-bones control room.

The first few years involved experimenting with the plasma and how to operate such a large fusion device (and of course, this still goes on), but since then, there have been several other notable events at JET…

In 1991 on the 9^th of November, JET was the first tokamak to use a deuterium and tritium fuel mixture (also known simply as DT), releasing 1.7MW of power for a short time. The deuterium and tritium fusion reactions occasionally used in JET and planned for more extensive use in ITER are the best balance between power output and ease of producing the right conditions in a tokamak for sustainable fusion.

1993 saw an almost entirely new machine setup, with the introduction of the divertor – a system initially thought to be useful to remove impurities and waste helium, but which also turned out to be extremely helpful in making more efficient fusion plasmas by having an effect on plasma density. JET wasn’t originally designed with a divertor, so the whole system had to be constructed inside the vessel, as it would have taken too long to take the tokamak apart to install it. Luckily, there was enough mechanical engineering expertise (and space!) to add this brand new system without dismantling the whole tokamak.

 

The JET Mark 1 divertor is the flat ring at the bottom of the vessel.

During September in 1997, JET achieved a record amount of fusion power using DT fuel: a peak output of 16.1MW, and a record JET still holds. This is enough to power just over 7400 UK homes*.

More recently, the 4000 or so carbon fibre composite wall tiles inside the vacuum vessel were replaced between 2009 and 2011 with a remote handling system (an industrial-strength version of the RIFT project). The new tiles, acting as a trial run for the planned wall type in ITER, are mainly beryllium and tungsten and have been very successful so far.

 

The ITER-Like Wall in JET, made of beryllium and tungsten.

What about now? Well, we’re preparing for the next set of DT experiments, planned for 2017 – twenty years after the record breakers of 1997. These DT “campaigns”, as they are known, will be gathering data for physicists and engineers to allow them to plan the DT operations for ITER, providing us working on JET with an exciting and ambitious set of goals ranging from materials analysis to plasma control.

And what about the other tokamak I implied in this post’s title? That would be the Mega-Ampère Spherical Tokamak (MAST), and it’ll be featured in a later post!

* Based on average UK household usage of 19MWh per year in 2013. Source: Department of Energy & Climate Change, 2014. Energy Consumption in the UK (2014). Link 

All images courtesy of the European Fusion Development Agreement.