In physics and engineering there are many phenomena that are familiar on macroscopic scales, such as the transfer of heat in a coal power plant, or conversion of kinetic energy from a waterfall into hydroelectricity, but as things scale down further and further scientists encounter exotic phenomena that are not universally known, if at all. When researchers begin to run into problems they have never encountered before, new theoretical research is needed. This is especially true in fusion physics, where enormous temperatures reduce atoms to their constituent charged particles, form a plasma, and then interact via electromagnetic forces in unusual ways.

What is plasma?
Plasma is known as the ‘Fourth State of Matter’ in physics after solids, liquids and gases. When a gas is energised to the point at which electrons break free from their atoms it becomes ionised, forming a plasma. Plasma is the most common state of matter in the universe. The Sun, lightning, northern lights and electric sparks are all examples of plasmas.

Recent research in plasma physics led by Dr John Bissell from the Tipping Points project could help point physicists and engineers working on nuclear fusion projects, such as the National Ignition Facility (NIF) in the US, in the right direction. According to Bissell and colleagues from Imperial College London and the University of Oxford, researchers need to be aware of a range of phenomena that their models currently neglect if they are to better understand fusion plasmas. In particular, some answers may lie in resolving plasma instabilities, not least for Inertial Confinement Fusion (ICF) experiments like that at NIF, where plasma inside a gold can — or hohlraum — is heated by high energy lasers.

For starters, the basic theory behind how electrons transport heat in laser-fusion experiments is not always considered. Despite some progress made, NIF still has much work to do if it is to reach its goal of achieving ‘ignition’ (a self-sustained fusion reaction, or burn), and one of the reasons for this may be not fully accounting for how electrons transfer heat in the first place. In the absence of magnetic fields, ‘conductive’ or ‘diffusive’ heat flow is normally well understood: electrons collide with particles in the plasma, and as they spread through it they take energy with them. However, if a magnetic field is present, charged electrons can be ‘deflected’, complicating the process of heat flow.

This is important because concentration of heat is essential for igniting a fusion burn, and the intimate relationship between thermal energy and pressure means that localised ‘hot spots’ form interfering with fuel compression that is needed for fusion to take place. If ignition can be achieved it will bring nuclear fusion closer to becoming a reliable and powerful source of energy, perhaps capable of resolving some of the world’s energy problems, but that may only be the beginning. The dream of fusion is locked in with phenomena that in extreme physical conditions, such as those at NIF, can unexpectedly interfere with experimental design.

The fuel capsule is 2mm in diameter containing a super-cooled hydrogen fuel.

According to Bissell, it is often assumed that for a magnetic field to be present in a plasma, it must be imposed externally, but researchers sometimes ignore the fact that plasmas tend to generate their own magnetic fields, with consequences for the heat-flow required to make atomic nuclei fuse together. If researchers are neglecting the magnetic field generated by the plasma itself, then they may not be able to see some of the root causes of their problems.

Indeed, while ICF physicists recognise that magnetic fields do exist inside of the hohlraum, the effects of the field on laser-plasma interactions are not necessarily acknowledged.

“When they started working on NIF they assumed that they were talking about experiments where they could do very simple modelling and I think they’re beginning to realise that things
like electron transport, magnetic field generation, all these kinds of more exotic laser plasma phenomena, actually might be really key”, said Bissell.

In order to understand what researchers may be missing you need to look closely at how lasers heat up plasmas in the first place. Laser light itself is an electromagnetic wave that oscillates (or swings) back and forth in a constant rhythm. As the laser light passes through the plasma, it causes electrons to accelerate up and down like boats bobbing in a harbour, giving them energy. The electrons then collide with ions, which scatters their motion into thermal energy, a process known as inverse bremsstrahlung (IB) heating.

Close-up of the hohlraum used in NIF experiments.

IB heating is important for understanding the laser heating of plasmas in fusion experiments because it can distort the distribution of energies in the plasma. Bissell and colleagues note in their study that IB heated plasmas tend to have more slow electrons and fewer fast electrons, relative to other kinds of plasmas, and because fast electrons are responsible for most of the thermal energy transfer, heat flow in IB plasmas can be strongly suppressed by up to 80-90%. Given that IB is a key mechanism for heating inertial confinement fusion plasmas, this effect
could be significant: not only for heat-flow itself, but also for related phenomena, such as the generation of magnetic fields.

If the plasma exhibits temperature gradients (spatial variations in the temperature) and density gradients (spatial variations in the density) then these features can interact to generate a magnetic field. As noted earlier, this is important because heat-flow deflected by the magnetic field can further concentrate thermal energy, enhance the temperature gradient, and lead to even more field being generated via positive feedback, or instability. This is called ‘field generating thermal instability’ and although Bissell says that it isn’t really clear what’s determining the actual field, “…it could be contributing to field generation in ICF hohlraums, and if it’s doing that it could be important later on for drive uniformity” (compression of the fuel). “Instabilities are amongst some of the main problems with doing fusion”, he said. Another issue with ICF is in the techniques they’re using to model the distribution of electrons in the plasma.

Normally in a plasma the distribution of electron speeds follow what is known as a ‘Gaussian’ or `bell curve’, but the problem is that because the lasers fired at the plasma are of such high
intensity, it’s not Gaussian at all. When a plasma is heated by IB it generates more slow-moving electrons and fewer fast heat carrying electrons.

On the other hand, even relatively small numbers of very fast-moving electrons can be important, because they can transfer thermal energy without diffusing in the normal way. Much of the computational modelling at NIF fails to account for these effects, and for good reason: cost. The numerical calculations necessary for simulating inertial confinement fusion experiments are extremely expensive.

But Bissell thinks there’s a way of getting around some of the problems by including IB in the underlying physical description. “That’s something that can be implemented relatively
easily. And it could be important, especially at early times when IB has really dominant effects”, he said. But he admits that “while certain phenomena may be key at early stages in ICF experiments, they may not be as important later on”.

Nevertheless, physicists and engineers working on ICF projects probably would do best to listen to their theoretical colleagues, especially since ignition is proving far more elusive than anticipated. “They need to start getting more theorists onto this kind of area, and pay attention to complicated phenomena that require much more theoretical and experimental investigation”, said Bissell.

The study this article is based on is available for free online: http://dro.dur.ac.uk/10512/ 

For more information or questions about the study contact Dr John Bissell at the Institute of Hazard, Risk and Resilience, Durham University. Email: john.bissell@durham.ac.uk

Photos Credit: Lawrence Livermore Laboratory https://lasers.llnl.gov/

English language is well-known for its ‘mood words’. Anyone who reads poetry or other forms of literature will know quite well what I’m getting at. Try reading literary heavyweights such as Sylvia Plath, Virgina Woolf or Charles Dickens or Henry David Thoreau, not to mention playwrights such as Shakespeare, without encountering emotional expression.

Emotion can capture a time, place, event or person like no other. Try this excerpt from William Blake’s poem ‘Broken Love’:

’Dost thou not in pride and scorn

Fill with tempests all my morn,

And with jealousies and fears

Fill my pleasant nights with tears?

Definitely in the ‘sad’ category.

Since the study included American and British English books it compared how often mood words appear in both respective forms of English literature. And the winner is…

Difference between American English and British English 1900-2000. Figure a: Emotion words Figure b: Content-free words Figure c: Random sample Figure d: 100 largest agglomerations in the world

Americans by far have used more mood words than their ‘repressed’ cousins across the pond, but researchers found that the increase in American mood word use coincides roughly with narcissism and ant-social sentiments in US population song lyrics from 1980-2007. Maybe NWA helped tip the scales with ‘F*** the Police’ or Guns and Roses with their debut album ‘Appetite for Destruction’, sung by probably one of the most narcissistic singers who ever lived. Perhaps the angst-driven lyrics of Nirvana and similar bands also deserve some credit for popularising sentiments originally associated with punk rock that are often interpreted as ‘anti-social’.

In the 1960s and the 1920s the study found a ‘happy peak’ (let’s hear it for counterculture!) where mood words associated with happiness were used more often in books. There is also a ‘sad peak’ corresponding with the Second World War, note the severe drop in ‘happiness’ around 1939.

While all mood words have been used less and less frequently since the early 20th century, ‘fear’ has hung on actually gaining in popularity since the 1970s. With fear leading the pack could it signify the growing anxieties of contemporary society?

Because the volumes of data on book words from Google Books is so massive, it is likely safe to assume that the use of language in books are an indicator of culture more generally.  So in this case book words certainly reflect various fears that have plagued western society for some time including nuclear war, terrorism and climate change.  The more quality data available to researchers, the more confidence they can have in their findings. But there is one caveat: if words change meaning more frequently in coming years then it will be more difficult to do this kind of research. Take ‘wicked’ for example, which was normally associated with a negative emotion, but is now used to describe something people are excited about. In slang, ‘bad’ can mean ‘good’ depending on the context in which it is used.

There is no direct explanation as of yet for why this the use of mood words is going down in English books.  Researchers also used contemporary mood word lists from Twitter data to describe recent events, but no increase in usage was found.

Guest editor, Marc Botha (Durham and Pretoria, Work Package 5 Researcher on Tipping Points)

 The characteristic fragility of human existence has always been marked by a deep ambivalence regarding the future. On the one hand, ceaseless crisis and catastrophe appear to justify a pervasive pessimism, while on the other, it is difficult not to marvel at the seemingly boundless human capacity for novelty, invention and change. Literature, in particular, has the unique capacity simultaneously to exemplify and critically examine the fragile co-existence of utopian and dystopian visions of the future. Indeed, the literary imagination has the ability to negotiate the multiple valences of the past, the contingencies of the present and alternate visions of the future.

The English Academy Review proposes to investigate the relation between literature, fragility, and the future in a special issue on Fragile Futures. We invite essays of up to 5000 words which interrogate how literature, criticism and theory have or might be able to clarify historical fragilities and to confront the fragility of the future, to offer forms of regional or global resistance to crisis or catastrophe, and to foster resilience and hope with respect to the fragile future with which we are all confronted.

Submissions should reach The English Academy Review by 31 MARCH 2014 and should be submitted electronically as a Word document to englishacademy@societies.wits.ac.za as well as in hardy copy to the following address:

English Academy Office

P.O. Box 124

Wits

2050

Johannesburg, South Africa

Please see the journal’s website at Taylor and Francis for further information on the preparation of manuscripts.

http://www.bbc.co.uk/programmes/p013bkmt

Paul currently has a new book available on networks:

Positive Linking: How Networks Can Revolutionise the World

Similar to pop music or designer clothes words go in and out of fashion over time. The popularity of certain words is often associated with the cultures that first used them. With the advent of Google Books, Twitter, Facebook and many others, new data is available for studying how these trends spread. These vast reservoirs of digital data that show what words are coming in or going out of style can be used as an indicator for cultural trends in society, such as the adoption of climate science by the public.

Climate science has been persistently in the media spotlight. It is not only a scientific, but political topic that is pressuring governments to come up with a plan to mitigate greenhouse gas emissions, but to adapt to a changing climate.

In a new study from the Tipping Points project at Durham University’s Institute of Hazard, Risk and Resilience, published in the journal PLOS ONE, Prof Alex Bentley (University of Bristol) and Dr Philip Garnett along with colleagues from the University of Missouri, Professor Michael J. O’Brien Professor and William A. Brock, have found that usage of some of the most popular keywords from climate science have dropped in popularity significantly, which may be an important indicator for how climate sciences needs to be communicated more effectively for it to have a greater societal impact.

In order to examine the ‘boom and bust’ of popular terms in climate science, researchers sampled a series of climate science terms from a random selection of books from the Google N-Gram database, that contains over 5 million books published in seven languages since the 1500s (about 4 percent of all published books). This massive set of data that includes word frequencies in books published up to 2008 allowed researchers to look at the evolutionary history of how frequently climate science words are used. It also provides insight into whether certain terms were learned socially, in other words copied by many different people, or were chosen independently of their social context.

The use of climate science words has grown considerably over the years with 793,000 different climate science terms published in 1700 compared to 5.46 trillion words in 2000, which of course includes the impact of the printing press and later digital publishing. While raw word count data alone says little about how the usage of words spread they do reveal word frequencies that are unique.

Popularities of top one-word climate science terms from Google N-Grams.

Researchers focused on the top one-word climate science terms for the period 2004-09 such as adaptation, biodiversity, climate and drought. They were interested in how these popular climate science words diffuse socially leading to their more general use outside of scientific research. They modelled the frequency of the climate science words over time to find out how popular they were, but also how the words themselves were used because how they are picked up socially may be key for allowing them to be used by non-scientists.

Since 1900, among the climate science words sampled by researchers, the ones that have been used steadily in published books are climate, diatoms and pollen. Some of the words like biodiversity were found to have started and stopped at different time periods instead of gradually increasing in frequency, but others were less consistent. For example, the popularity of precipitation, photosynthesis, and adaptation started at different times from the late 1800s to 2000. These charts show the frequency of some of  the terms mentioned.

While authors of the study argue that the usage of climate science terms is determined by social learning rather than individual decision-making, future research needs to further identify whether this is the case. They recommend that in order to encourage interest and support for the findings of climate change science widely, an approach that accounts for how information about climate change spreads through social learning is needed to allow the public to learn about climate change themselves in their respective communities.

The study ‘Word diffusion and climate science’ is freely available online from PLOS ONE here.

And in case you missed Part 1:

As part of the 2012 Tipping Points Conference held at Durham University, Prof Patricia Howard gives an inspiring keynote presenting the role of biodiversity in human societies. Howard explores the notion of ‘biodiversity tipping points within the context of indigenous communities and species focusing on where human culture and nature meet forming a unique ecological relationship that people depend upon for survival.

It features the latest research updates from all five work packages of the project:

• - Trust and maintaining resilience of financial markets

• - Development of UK banking sector

• - Field research on past climate in the North Atlantic

• - Tipping points in populations of UK banks and ‘titanic moments’

• - Use of ‘tipping point’ in popular culture and in discussions about climate change

Plus much more!

Tipping Points Annual Report 2011-12