Week 16: Collecting light

Added February 12th, 2010 in Shutdown Weekly

In this week we change the venue and take a two minutes walk from the Torus Hall to former offices in the same building. Over the last two years these were converted into laboratories and now host instrumentation to collect light from inside the vessel; light which is going to be emitted by ‘impurities’ from the new beryllium and tungsten tiles being installed.

When beryllium and tungsten are eroded by interaction with ions and electrons, the atoms emit characteristic light as they enter the plasma. The intensity and the wavelength tell the physicists about type and quantity of erosion. The experiments of JET’s carbon era saw red, green and blue wavelengths of carbon impurities and these were well monitored by existing diagnostics. This set-up has to be adjusted to the materials of the new ITER-Like Wall. Tungsten atoms, for example, emit light at violet wavelengths. With the help of 2 kilometres of fragile optical-fibres the team will be ready to collect the light with the first pulse foreseen in 2011. Costanza Maggi emphasises another aspect “A lot of the diagnostics here at JET are located directly in the Torus Hall, exposed to magnetic fields. We take advantage of a separate laboratory well protected from these influences and equipped with its own air conditioning.”

The related enhancement project “Spectroscopy in support of the ITER-Like Wall” is run as a collaboration between scientists from the Culham Centre for Fusion Energy (United Kingdom), Forschungszentrum Jülich (Germany) and Vetenskapsradet (Sweden). The installation of the new equipment in the laboratories is now in its final stages and calibration of the new systems, using a light source operated by Remote Handling, is planned for later this year.

Background information
“Shutdown” in JET terms means to close the experiment down periodically to maintain and upgrade the fusion device. After this period experiments are going to be performed leading to better understanding of how to build and operate JET′s successor ITER. The current shutdown started on 26 October 2009. It is the fifth to be carried out remotely since commissioning JET in 1983. During the shutdown 86,000 components will be changed inside the JET torus.