With the latest set of experiments carried out in April 2009, JET has operated close to its technical limits and, therefore, closer to ITER conditions.

Experiment with 4.3 Million amperes at JET (Picture: JET).

In cranking JET up to H-mode operation, the JET researchers brought the plasma current up to 4.3 million ampere whilst applying the full magnetic field of 3.45 Tesla. This gets close to the machine’s limit and requires very careful operation. It took a total power of 27 megawatts injected into the plasma, with 23 megawatts coming from the increased neutral beam power and another 4 megawatts provided by radio frequency power. In such an operation, the conditions in JET are closer to ITER and it is possible to study phenomena which will be crucial to ITER. For example, very large edge localised modes (ELMs) may occur, which cause a heat pulse at the divertor similar to the maximum level ITER is able to tolerate.

The divertor is that part of the machine which is designed to accept the exhaust of energy and fuel. For the first time in JET, a new infra red camera enabled measurement of the temperature of the divertor targets and investigation of the erosion of material from these targets. These studies will provide a comparative basis for JET experiments which follow on from the installation, later this year, of a new divertor and interior wall made of the materials intended for ITER. For the experiment described, which was conducted in deuterium, it was further found that high input power (relative the threshold for entering H-mode) is required to sustain the steady state plasma performance which is necessary for a fusion power plant. This ratio of input to threshold is important when it comes to defining the heating power that will need to be installed in ITER.

Thanks to Petra Nieckchen for her inputs.