Posted on: 8th October 2012
Latest results from the Joint European Torus (JET) fusion device are giving researchers increasing confidence in prospects for the next-generation ITER project, the international experiment that is expected to pave the way for commercial fusion power plants. Operation with a new lining inside JET has demonstrated the suitability of materials for the much larger and more powerful ITER device. Today Dr Francesco Romanelli, Leader of the European Fusion Development Agreement (EFDA) and JET Leader, will deliver a summary of the JET results at the IAEA Fusion Energy Conference in San Diego, U.S. This major fusion conference is held every two years and aims to discuss various options with the goal of building the first demonstration power plant before the middle of the 21st century.
JET, Europe’s premier magnetic confinement fusion facility, based at Culham, UK, has completed eleven months of tests to simulate the environment inside ITER and to prototype key components. For this purpose JET has been successfully transformed into a ‘mini-ITER’ with a wall made of the same materials – beryllium and tungsten – that ITER plans to use. Initial results will be summarised by Dr Francesco Romanelli, Leader of the European Fusion Development Agreement (EFDA) and JET Leader, at the IAEA Fusion Energy Conference in San Diego, U.S. on Monday 8 October.
At the heart of tokamak fusion reactors like JET is a ring-shaped vacuum vessel in which very hot plasma is confined using magnetic fields. Selecting the correct materials for the inner wall of this vessel is essential. Firstly to minimise ‘pollution’ when small amounts of wall materials enter the plasma, and secondly to prevent the fusion fuels from becoming trapped in the wall. ITER will use beryllium for the main wall and tungsten (with its higher melting point) for the floor of the chamber – the ‘divertor’ – where plasma is exhausted and heat loads are greatest. A 20-month engineering upgrade during 2010 and 2011 installed a new plasma-facing wall inside JET to validate these materials for ITER.
From the first test in August 2011, the beryllium and tungsten lining enabled more reliable plasmas to be produced. Crucially, researchers from the 27 European fusion laboratories which participate in JET have found that the amount of fuel being retained in the wall is at least ten times less than in the previous, carbon-based, configuration. The results achieved may lead ITER to drop plans for an initial phase of operation with carbon and adopt a beryllium-tungsten wall from the outset, bringing a significant saving in time and cost for the project.
Experiments at JET will restart in early 2013, with the goal of demonstrating further improvements in plasma performance, beyond expectations when scaled up to ITER. Looking further ahead, EFDA is already planning a full ‘dress rehearsal’ for ITER – an experimental campaign at JET using the optimum deuterium-tritium fuel mix that is needed for high-power fusion operation. JET is the only device currently able to run fusion plasmas with tritium, and exploiting these capabilities will be a crucial part of ITER preparations. ITER Director General Osamu Motojima praised the work being done at JET during a visit this summer and has been discussing collaborations with EFDA on future experiments.
Dr Francesco Romanelli said: “These results are very encouraging for ITER. JET is getting as close to ITER conditions as any present-day fusion device can. If this performance is scaled up, ITER will be successful and take a huge step towards the goal of commercial fusion power.
“JET has largely formed the basis for ITER’s design and is an ideal test-bed. We hope to open up new collaborations with ITER partners as we prepare for full deuterium-tritium tests in 2015. Already we are working with Indian colleagues on magnetic coils for suppressing plasma instabilities. I hope to build more partnerships so JET’s unique capabilities can be used for the benefit of the worldwide fusion programme.”
European research developing magnetic confinement fusion as a sustainable energy source is co-ordinated through the European Fusion Development Agreement (EFDA – www.euro-fusion.org). The flagship of this programme is the Joint European Torus (JET). JET is the largest and most powerful fusion research facility in the world and the only machine capable of operating with the deuterium-tritium fuel mixture that will be used in commercial fusion power stations. Scientists and engineers from associated laboratories across Europe and international collaborators carry out experiments on JET within an integrated and co-ordinated EFDA programme. The machine operation and on-site services are provided by Culham Centre for Fusion Energy (www.ccfe.ac.uk) in Oxfordshire, United Kingdom on behalf of its partner European fusion laboratories.
Research at JET is focused on scientific and technical preparations for the operation of ITER (www.iter.org), a major international project that should provide a full scientific demonstration of fusion in power plant-like conditions. ITER construction started in 2008 at Cadarache, France, and the first plasma is scheduled for 2020.
Energy is released when two light atomic nuclei are fused together to form one heavier atom. This process takes place in the Sun and the stars. In a fusion reactor nuclei of two hydrogen isotopes, deuterium and tritium, fuse at high temperatures and produce helium and high-energy neutrons. A commercial power station will use the heat generated by the neutrons when slowed down by a blanket of denser material (lithium) to generate electricity.
To produce enough fusion reactions to make a useful energy source the fuel must be heated to temperatures in excess of 100 million degrees. At these temperatures the extremely thin gaseous fuel exists in the form of plasma that can be confined by means of magnetic fields to keep it from being contaminated and cooled by contact with material surfaces. Most magnetic confinement systems are toroidal (doughnut-shaped) and the most advanced is called the tokamak. JET is the largest tokamak in the world.
The fuels used are virtually inexhaustible. Deuterium is extracted from ordinary water and tritium can be produced from lithium, a common metal found in the earth’s crust. Combined in a fusion power plant, the lithium in a phone battery and three litres of water would give a European person all the electricity they need for seven years. Fusion is inherently safe and environmentally responsible. No greenhouse gas or long-lived radioactive waste is produced and not even the worst accident would require evacuation of the surrounding population.