Fast action thanks to expertise

Fast action thanks to expertise

Within only three months KFKI-RMKI successfully designed and installed a prototype system for Beam Emission Spectroscopy on the Korean experiment KSTAR. Now the project has received additional funds to build a fully developed system.Scientists at the Hungarian Associate KFKI-RMKI are experts in Beam Emission Spectroscopy, a technique for investigating plasma turbulence. In 2010, together with the Korean National Fusion Research Institute, they received a starting grant to evaluate the prospects of such a system for the Korean tokamak KSTAR and to develop a conceptual design for it. The project was supported through a fund for joint scientific actions, set up by the Hungarian Academy of Sciences and the Korea Research Council of Fundamental Science and Technology.

Beam Emission Spectroscopy (BES) measures light emitted from the neutral particle beams which are injected into the plasma for heating or diagnostics. Along the way, the particles collide with plasma particles, get excited and emit light. The intensity variations of these emissions reflect the local density fluctuations, from which plasma turbulence can be measured. Turbulence causes the plasma to lose heat and particles and is therefore one of the most scrutinised effects in fusion science. The challenge for BES diagnostics lies in the very low light levels, which require extremely sensitive detectors.

15 years of experience

KFKI-RMKI has been developing BES diagnostics for 15 years and installed such systems on various tokamaks in Europe. Together with its spin-off company Admintech Kft, the Associate developed a highly sensitive detector. It greatly enhances the capability of BES systems and was installed on MAST in 2010. A similar detection system is currently being installed on JET.

Based on an existing BES code, the team from Budapest University of Technology and Economics developed a simulation model for the KSTAR system. The calculations of the expected light intensity, spectrum, spatial resolution and other parameters were discussed in April 2011 and the team concluded that the system would offer good measurement possibilities. Timing however, presented a challenge: KSTAR’s experimental campaign was to end in early September and the next one would not start for another year. Within three months, the team designed, built and installed a trail BES system on KSTAR. Luckily, a test sample of the detector was available at Admintech Kft and RMKI could design an affordable optical system based on off-the-shelf components.

Unusual cabin baggage

In July, Project Leader Sándor Zoletnik and a design engineer hand-carried the heavy 60 kilogram system to Korea. With the help of the Korean project leader Yong Un Nam, the system was installed in the port and connected to the control computer within one week. Experiments started in the first days of August and the system operated throughout the remaining campaign. First analysis showed that the measurements fitted the model calculations. Because RMKI had developed analysis software for previous BES experiments, scientists could immediately begin to use the data to study plasma phenomena. In July 2011 the project received resources for one more year to build a final BES diagnostic for KSTAR.

Contact: Sándor Zoletnik, zoletnik@rmki.kfki.hu