World’s largest test facility for negative ion sources opens to develop heating for ITER

The half-size test facility of the ITER Neutral Beam ion source, ELISE (Extraction from a Large Ion Source Experiment), has been inaugurated at the Max Planck Institute for Plasma Physics (IPP) in Garching, Germany. ELISE is a key experiment in conducting research to develop one of the main heating systems of ITER – the neutral beam injector – which will contribute heating the plasma to million degrees necessary for a fusion reaction to occur. ELISE is funded by F4E by means of a contract worth about 4 million EUR and coordinated at a technical level by Dr Antonio Masiello of F4E’s Neutral Beam and EC Power Supplies and Sources project team.

Today’s existing neutral beams devices can contribute to reaching temperatures which are a fraction of that of the sun. However, new and more demanding requirements on the hydrogen atoms being injected into the plasma and transferring their energy to the plasma through collisions, will need to be used when operating ITER. Indeed, the ITER machine will necessitate that the particles are about one order of magnitude faster so that they can penetrate deep enough into the voluminous plasma in order to heat it. Instead of the electrically positively charged ions used to accelerate the particle beam (the beam used to inject the hydrogen atoms), ITER will use extremely fragile negatively charged ions. A prototype for a new type of source in which the ions are generated by a Radio Frequency (RF) electromagnetic field was firstly developed at IPP for this purpose. The successful experiments carried out on the prototype led to a change in 2007 of the ITER baseline design: the so-called “arc driven” ion source (in which the ions were generated by means of an electric discharge) was replaced by the more promising RF source. The ELISE test facility was then conceived as an intermediate step in order to adapt the prototype to match ITER’s requirements.

As the world’s largest system of its kind, ELISE has taken three years to be assembled. The system’s core is uniquely comprised of 640 ion beamlets, making up one beam which has an intensity of up to 20A and with energy up to 60keV. The overall beam has an area of approximately 1 m2 and can reach 1.2 MW of power. Each of the two foreseen Neutral Beam systems for ITER will deliver 16.5 MW heating power to the plasma. ELISE represents therefore a significant improvement from the previously operating devices whose beam size is approximately one order of magnitude smaller.

Now that ELISE is inaugurated, IPP researchers will spend the next two years studying whether the new ion source can generate a particle beam approaching ITER’s requirements. The experiments on ELISE are extremely important to give new insights for the construction, assembly and operation of the next step devices, such as the full-size prototype of the ITER source, SPIDER, which will start operation in 2015 at the Consorzio RFX research institute in Padova, Italy.