In December 2005 the project “Fast camera for pellet, plasma-wall and fluctuation studies”, led by CIEMAT (the Spanish Association), and with the collaboration of IST and HAS, (the Portuguese and Hungarian Associations), was launched as a part of the “Diagnostics in Support of the ITER-Like Wall” package. This package of projects is an element of the JET Enhancement Programme 2, consisting of three major-scale and seventeen medium-scale projects.
In September 2006, a Photron APX-RS camera was installed in JET. The camera is located near the equatorial plane. Its maximum recording speed is 250 kHz and its minimum exposure time is 1 microsecond. During the JET Restart in autumn 2006 the camera produced its first results. In February 2007 it was a very important diagnostic in JET’s disruption experiments.
Under some conditions the plasma in a tokamak can become unstable, which causes the complete loss of its thermal and magnetic energy. These events are called plasma disruptions. In ITER, the expected energy fluxes and mechanical loads during disruptions on components installed inside the vacuum vessel pose significant challenges for their design. These phenomena can decrease the lifetime of machine elements, especially those of the First Wall or in the divertor region, thus increasing the need for maintenance or repair. Additionally, the operating space of the device can be limited. Therefore JET is carrying out experiments to determine the key physical processes that determine the fluxes of energy during disruptions, to provide a basis for the estimation of these energy fluxes for ITER, and to develop methods to control or minimise them.
New diagnostics at JET like the fast visible camera are providing new measurements that aid the understanding of phenomena during disruptions. The camera allows, for the first time, insights into the dynamics of the plasma-wall interaction, as can be seen in this movie: