Gaia Vince watches the construction of the world’s biggest fusion energy reactor and wonders whether this ambitious and expensive project will actually work.

Cadarache: In the dusty highlands of Provence in southern France, workers have excavated a vast rectangular pit 17 metres (56 feet) down into the unforgiving rocks. From my raised vantage point, I can see bright yellow mechanical diggers and trucks buzzing around the edge of the pit, looking toy-like in the huge construction site. Above us, the fireball Sun dries the air at an unrelenting 37C.

These are embryonic stages to what is perhaps humankind's most ambitious scientific and engineering project: to replicate the Sun here on Earth.

When construction is complete, the pit will host a 73-metre-high machine(240 feet) that will attempt to create boundless energy by smashing hydrogen nuclei together, in much the same way as stars like our Sun do. Physicists have dreamed of being able to produce cheap, safe and plentiful energy through atomic fusion since the 1950s. Around the world, researchers continue to experiment with creating fusion energy using various methods. But as people within the field have said the dream has always been "30 years away" from realisation.

The need for a new energy source has never been more pressing. Global energy demand is expected to double by 2050, while the share coming from fossil fuels – currently 85% – needs to drop dramatically if we are to reduce carbon emissions and limit global warming.

Fusion, many believe, could be the answer. It works by forcing together two types, or isotopes, of hydrogen at such a high temperature that the positively charged atoms are able to overcome their mutual repulsion and fuse. The result of this fusion is an atom of helium plus a highly energetic neutron particle. Physicists aim to capture the energy released by these emitted neutrons, and use it to drive steam turbines and produce electricity.

When the reaction occurs in the core of the Sun, the giant ball of gas applies a strong gravitational pressure that helps force the hydrogen nuclei together. Here on Earth, any fusion reaction will have to take place at a tiny fraction of the scale of the Sun, without the benefit of its gravity. So to force hydrogen nuclei together on Earth, engineers need to build the reactor to withstand temperatures at least ten times that of the Sun – which means hundreds of millions of degrees.

Heated doughnuts

It's just one of the huge number of challenges facing the designers of this groundbreaking project. The concept was discussed and argued over for several decades before finally being agreed in 2007 as a multinational cooperation between the European Union, China, India, Japan, South Korea, Russia and the US – in total, 34 countries representing more than half of the world's population. Since then, the budget of 5 billion euros has trebled, the scale of the reactor has been halved, the completion date has been pushed back, and the project has somewhat lost its shine – which is somewhat ironic given the project is called Iter, meaning 'the way' in Latin.

But despite the difficulties, some progress is being made. The parts are being manufactured and tested by the participating nations, many of whom hope to develop the expertise to compete in any new fusion energy market that would be expected to follow a successful outcome at Iter.  

Since they don't have access to the special conditions available in the Sun, physicists have designed a doughnut-shaped reaction chamber, called a tokamak. Hydrogen isotopes are heated to the point to which they lose electrons and form a plasma, and this is held in place for fusion but held away from the reactor walls, which could not withstand the heat. The tokamak deploys a powerful magnetic field to suspend and compress the hydrogen plasma using an electromagnet made of superconducting coils of a niobium tin alloy.

Once atomic fusion occurs, the heat produced will help to keep the core hot. But unlike a fission reaction that takes place in nuclear power stations and atomic bombs, the fusion reaction is not self perpetuating. It requires a constant input of material or else it quickly fizzles out, making the reaction far safer. And unlike what you might have seen in a recent Batman movie, the chamber cannot be transformed into a nuclear bomb. The neutrons will then be absorbed by the surrounding walls of the tokamak, transferring their energy to the walls as heat, and this in turn will be dissipated through cooling towers.

Because one of the hydrogen isotopes used, tritium, is radioactive (with a half-life of 12 years), the entire site must conform to France's strict nuclear safety laws. And to complicate matters further, the site is also moderately seismically active, meaning that the buildings are being supported on rubber pads to protect them from earthquakes.

These issues, plus the logistics of dealing with multiple nations with their own fluctuating domestic budget constraints, mean that the site won't be ready for the first experiments until 2020. Even then, they will just be testing the reactor and its equipment. The first proper fusion tests, reacting deuterium (a hydrogen isotope abundant in sea water) and tritium (which will be made from lithium), won't take place until 2028.

Power up

Those will be the key tests, though. If all goes to plan, the physicists hope to prove that they can produce ten times as much energy as the experiment requires. The plan is to use 50 megawatts (in heating the plasma and cooling the reactor), and get 500 MW out. Larger tokamaks should, theoretically, be able to deliver an even greater input to output power ratio, in the range of gigawatts.

And that is the big gamble. So far, the world's best and biggest tokamak, the JET experiment in the UK, hasn't even managed to break even, energy-wise. Its best ever result, in 1997, achieved a 16 MW output with a 25 MW input. Scale is an extremely important factor for tokamaks, though. Iter will be twice the size of JET, as well as featuring a number of design improvements.

If Iter is successful in its proof of principle mission, the first demonstration fusion plants will be built, capable of actually using and storing the energy generated for electricity production. These plants are slated to begin operation in about 2040 - around 30 years away, in fact...

Despite the seductive promise of finally getting a supply of electricity that's "too cheap to meter", the long wait to readiness and the fact that the technology remains unproven, means that many politicians are hesitant or even hostile to the expensive project. Additionally, because fusion energy won't be ready for decades, even if it works, other low-carbon energy sources must still be pursued in the short-term at least.

But if we do manage to replicate the Sun on Earth, the consequences would be spectacular. An era of genuinely cheap energy – both environmentally and financially, would have far reaching implications for everything from poverty reduction to conflict easement.

It’s exciting to think that the next generation could in some way be fusion powered – perhaps even within the lifetimes of the workman digging below me. But I can’t help but remember the 30-year rule.

Sourve: BBC

Defrosting the freezer is one of those summer tasks that everyone has to do, and JET is no exception. Its “freezer” is set of panels that make up the cryo pump, a crucial part of the system that keeps the inside of the JET vessel at an extremely low vacuum. Over the course of 11 months of experiments quite a build up of frozen material forms, so one of the first jobs to perform now that experiments have finished is to warm up the cryo panels, and melt the frost deposits.

But it’s more than just a chore, the material that has accumulated on the panels tells a story about what has been going on in JET’s plasma chamber. This means that as soon as experiments ceased the Active Gas Handling team swung into action, working round-the-clock shifts to capture and analyse the gases being released as the cryo pumps warmed up. Most of it of course will be the deuterium fuel, but there will be other constituents used in the experiments, for example argon or nitrogen, or maybe even carbon or tritium from previous experimental campaigns.

There will also be combinations of all the above species. Hydrocarbons are well known at JET – in fact they are one of the reason that carbon was replaced in the vessel by the ITER-Like Wall. The recent experiments using nitrogen seeding may well lead to the formation of ammonia (a compound of nitrogen and hydrogen) so its collection will also be under scrutiny.

Every substance will have a story to tell about the processes that happen in a plasma at 100 million degrees, and so the analysis in the next couple of months will create another piece in the jigsaw of fusion energy research.

Source: EFDA

A group of physicists from Switzerland, Japan, Russia, US and the UK has proposed using the tunnel that currently houses the Large Hadron Collider (LHC) at the CERN particle-physics lab near Geneva for a dedicated machine to study the Higgs boson. The facility, dubbed LEP3, is named after CERN's previous accelerator, the Large Electron–Positron Collider (LEP), which used to exist in the LHC tunnel before being shut down in 2000. In a preliminary study submitted to the European Strategy Preparatory Group, LEP3's backers say that the machine could be constructed within the next 10 years.

The plans for LEP3 come just weeks after physicists working at CERN reported that they had discovered a new particle that bears a striking resemblance to a Higgs boson, as described by the Standard Model of particle physics. The ATLAS experiment measured its mass at around 125 GeV and the CMS experiment at 126 GeV.

LEP3 would operate at 240 GeV and comprise two separate accelerator rings that would smash electrons and positrons rather than protons and protons, as with the LHC. In their study, the 20 authors call the concept for LEP3 "highly interesting" and that it deserves more detailed study. "Now is the right moment to get this on the table," says theorist John Ellis from Kings College London in the UK, who is an author of the preliminary study and hopes that it will trigger debate among physicists as to how to study the new boson in detail.

Tunnel vision

LEP3 is designed to be installed in the LHC tunnel and serve the two LHC's general-purpose detectors – ATLAS and CMS. If LEP3 is to be built, it will have to fight off two rival proposals for a future collider to study the Higgs – the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). But Ellis says that one advantage of LEP3 is that the tunnel to house it is already built and the collider would use the existing infrastructure, such as cryogenics equipment, thus making LEP3 more cost-effective. LEP3 would also use conventional electromagnets to accelerate particles rather than the accelerating superconducting cavities that will be employed by the ILC.

Which collider is built to succeed the LHC will depend on what the LHC discovers in the next couple of years after it has run at its full design energy of 14 TeV. If it turns out that the LHC finds only the Higgs, then Ellis says there would be a strong case for LEP3. But if more particles are discovered by the LHC – such as supersymmteric particles – it would make sense to consider the other two proposals. "LEP3 could be a more secure option than the ILC if only a Higgs is discovered," Ellis told physicsworld.com. "But, of course, it would be foolish to choose anything now, given that the LHC has not hit full energy yet."

CERN plans to run the LHC into the 2030s after it has undergone a major upgrade in energy and luminosity in the coming decade. However, Ellis thinks that it may even be possible for the LHC and LEP3 to cohabit for a short time. "It would not be ideal, but it could be something to think about," says Ellis. "If the LHC does not discover anything beyond the Higgs, then would you keep running it for years?"

"Little scope"

Yet some disagree that LEP3 represents the best way to study the Higgs, adding that a decision would have to be made between building LEP3 and running the high-luminosity upgrade to the LHC in the 2020s. "They both have an excellent physics case, but somehow LEP3 presents less chance of a huge breakthrough," says one leading CERN researcher who prefers not to be named. "[The LHC upgrade] has precision measurements as well as discovery reach to offer."

That view is shared by linear-collider director Lyn Evans, who toldphysicsworld.com that he thinks it is unlikely that the proposal for LEP3 will get very far. "The first job is to fully exploit the LHC and all its upgrades," says Evans, who led the construction of the LHC. "This is at least a 20 year programme of work, so I think that it is very unlikely that the LHC will be ripped out and replaced by a very modest machine with little scope apart from studying the Higgs."

Source: physicsworld.com

 Operating JET is like flying its namesake aeroplane. You need to take off and land safely – the part in the middle is comparatively easy. Ramping up the power too quickly can make for an unstable plasma, but too slow can allow contaminants to percolate into the plasma. And coming into land is tricky too, you can’t just turn off the system, you need to allow the power of the plasma to dissipate slowly and evenly. Getting the sequence of events just right is vital to the safe and productive operation of JET – at ITER with five times as much current in the plasma, even more will be at stake.

However, recent tests of JET operation have given the ITER team some encouraging results. To achieve ITER’s high level of fusion power, the proposal is to apply high-powered heating to the plasma a lot earlier in the pulse than is usually done at JET. This heating scenario was tested successfully four years ago at JET using carbon as first wall material.

However, carbon is not an ideal plasma-facing material, because it retains the fusion fuel. Recent experiments at JET have instead been testing tungsten as an alternative wall material for ITER – it is much less predisposed to bonding with hydrogen isotopes and has a very high melting point. However, because tungsten has many more electrons than carbon and therefore tends to radiate more, there were concerns that the tungsten impurities would lead to substantial energy loss from the plasma through radiation.

Hence, the experiments from four years ago were repeated with JET’s new tungsten divertor (area where the hot plasma interacts mostly with the wall).  Much to the relief of the ITER team, JET successfully demonstrated the feasibility of using early heating. In fact it seems the change from carbon to tungsten in the divertor may even give the operators a little more flexibility with their scenarios as the power required to obtain good plasma confinement is somewhat lower, an unexpected bonus!

Source: EFDA

Last week marks the end of the first period of JET operations with the all-metal ‘ITER-Like Wall’. The machine is now going into a period of several months of maintenance, ready to restart operations early in 2013.