World’s Largest Fusion Experiment Back in Operation

After an 18-month shutdown to upgrade the machine and four months of commissioning, the Joint European Torus (JET), the world's largest magnetic fusion device, is ready to start new experiments. The inside of the vessel now has a completely new wall. JET is the first fusion machine to test the materials that will be used inside the next-generation international experiment, ITER.

Last Friday, scientists from throughout Europe started the first experimental campaign at JET after the installation of the "ITER-Like Wall." The upgrade comprises new materials inside the JET vessel, more heating power and additional diagnostic systems.

JET's researchers are investigating the potential of fusion power as a safe, clean, and virtually limitless energy source for future generations. The research is coordinated under the European Fusion Development Agreement (EFDA).

EFDA Leader Francesco Romanelli commented: "This is probably the largest effort that has been put into JET apart from the construction of the machine itself. With the expertise and contribution of many fusion laboratories, the JET team has succeeded in building a small ITER. We had a very good start with high purity plasmas readily established in ITER relevant conditions -- a promising sign for the use of these wall materials in ITER."

The inside of the JET vessel is now made of beryllium and tungsten tiles forming an 'ITER-Like Wall'. Between October 2009 and May 2011 engineers from Culham Centre for Fusion Energy removed and replaced approximately 86,000 components, largely using remote handling technology.

Lorne Horton, Head of EFDA's JET Department, explained: "The coming experiments will aim to verify that the wall materials chosen for ITER will behave as expected." Beryllium is being used in the main wall, whereas tungsten, with its high melting point, is the choice for the exhaust component known as 'divertor' that has to withstand high heat flux.

The other main enhancement is a 50% increase in the heating power. With the extra power, JET will achieve higher plasma temperatures and approach ITER conditions. New diagnostics and control systems, developed by the EFDA associate laboratories, will allow a deep investigation of the scientific challenges in preparing for ITER.

Maximos Tsalas is one of the visiting scientists in the control room. He has worked for many years at JET and has recently moved to FOM Rijnhuizen, in The Netherlands. He explained: "I left JET more than a year ago. Coming back, the developments I see are amazing. JET has become a brand new machine. I feel extremely privileged to take part in the first set of experiments. The coming campaign will be very challenging, and we are all eager to see how the new systems perform and to learn how to operate with the new wall."

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