Galeria

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.

Last week JET performed its last experiments until 2013. But, as JET shuts down and many of the scientists return to their homes across Europe and embark on summer holidays, the work does not stop.

“We’ve ticked all the boxes for the ITER-Like wall” says Task Force Leader Guy Matthews. JET Department Leader Lorne Horton agrees: “It wasn’t at all obvious that it would go this well! However the experiments have also thrown up a couple of surprises that we will need to look into.”

During the shutdown many of JET’s systems are being upgraded or refurbished. New systems are also being installed or calibrated, especially those that measure gamma rays and neutrons, as JET gears up for deuterium-tritium experiments in 2015. Also tiles will be extracted to examine in detail the wear and tear sustained during these experiments – vital information for evaluating the new ITER-Like wall.

Scientists will also continue analysing the large amounts of data accumulated during the eleven month campaign, checking calibrations and making careful comparisons with previous experiments conducted with the old carbon wall.

Then planning for next year’s campaign needs to be done. Initial meetings have happened, so the task force leaders will use the summer to make detailed plans for the campaign. Already staff from ITER have been involved, requesting certain experiments relevant to ITER be performed to give them more information on which to base their design decisions.

With all this going on, it’s clear every fusion scientist needs to find a good sized-beach to jot down their future research plans!

Source: EFDA

To create fusion, you need a very different world to the one we live in. It needs to be six orders of magnitude hotter and six orders of magnitude less dense – and the result is six orders of magnitude more energy than most everyday processes.

The temperature required for fusion is over 100 million degrees. In the heat of Oxfordshire summer outside JET it might even reach 25 degrees Celsius, or 298 degrees Kelvin – which some people find hot – but it is still 6 orders of magnitude colder than the core of a fusion plasma.

One might expect that the pressure in a fusion tokamak must be very high – similar to the core of the sun. In fact it’s the opposite: the optimum density for fusion is about 10⁶ times less than that of our atmosphere. The reason for this surprising fact is that higher density means more collisions between particles. Of course collisions between ions are good, because they are what leads to fusion. However when the ions in the plasma collide with electrons, energy is lost. This is because of a process known as bremsstrahlung, or “braking radiation”, which refers to radiation that is caused by charged particles changing direction – for example during a collision.  In a plasma at the extreme temperatures required for fusion, the high speed of the electrons means they emit X-rays when they collide with a nucleus; if the density gets too high, there are so many collisions that the energy of the plasma is lost due to all the resulting X-rays.

Having created an environment six orders of magnitude hotter and six orders of magnitude less dense than our everyday world, the result is energy in quantities six orders of magnitude greater than most common processes. Plasma physicists measure energy in electron volts – in other words the energy that one electron would acquire if powered by a one volt battery. Batteries are powered by chemical processes – by combining a number of electrochemical cells we can create powerful batteries such as those in a car, which have a voltage of 12 volts. Burning coal creates about four electron volts. But the products of the fusion, powered by nuclear processes, have a staggering 17.6 million electron volts. In other words you would need to connect well over a million car batteries to give particles the same amount of energy  as that released when deuterium and tritium fuse.

So it seems the conclusion to draw is that, although achieving fusion sometime seems six orders of magnitude harder than burning fossil fuel, it will be a milliion times better in the long run!

Source: EFDA

The Director General of ITER, Osamu Motojima has praised work done at JET during a visit there on Wednesday the 11th of July. “It’s encouraging to see the results from JET’s ITER-Like Wall that have been achieved in such a short space of time” he said during a presentation to staff, continuing that  “ITER is dependent on the success of JET.”

Motojima-san visited JET with two senior staff, Director of Plasma Operation, David Campbell, and Senior Scientist in Plasma Confinement Alberto Loarte. To a packed lecture hall Motojima-san outlined ambitious plans to keep the ITER project on schedule, while Dr Campbell spoke of the science challenges for ITER. “We are keen to work very closely with the JET team on issues such as disruptions, ELMs and melting studies” he said. “The work JET is producing is of a high level. It is extremely impressive and will be important for the exploitation of ITER. I encourage you to carry on along the same path.”

An objective for the visit was to discuss possible future collaborations between ITER and JET.  At the last ITER Council meeting, it was agreed that ITER should join the IEA implementing agreement on Cooperation on Tokamak Programs.  The agreement provides a legal framework for participation of ITER Organisation staff in experiments on JET that are targeted at addressing specific issues of interest to ITER.  Thus, the Director General’s visit allowed timely discussions on how to deepen collaborations between JET and ITER.

Source: EFDA