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From 2020 onwards, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ fusion reactor will demonstrate how nuclear fusion can be used as an energy source. However, inside the reactor, the plasma at a temperature of 100 million degrees presents scientists with huge challenges. Direct contact would destroy important optical instruments within a short period of time.

 

At the 27th Symposium on Fusion Technology (SOFT), from 24-28 September 2012 in Li¨¨ge (Belgium), J¨¹lich researchers are showing how the delicate instruments can be protected by means of new shutter and cooling systems. Among other options, they will present a patented shutter controlled by a pneumatic cylinder which was developed specifically for ultra-high vacuum.

 

 

Optical monitoring methods are indispensable for assessing the plasma properties and composition. However, optical elements in the vicinity of the plasma are exposed to extremely high loads. The plasma, largely composed of hydrogen and helium nuclei, erodes part of the surface material but also deposits contaminants. Thermal energy must be continuously removed in order to keep the temperature constant.

 

"The greatest technological challenge is to find suitable materials and designs to protect and cool the optical elements that can also be cleaned when they are installed in the machine," explains Dr. Olaf Neubauer from the J¨¹lich Institute of Energy and Climate Research, Plasma Physics (IEK-4). Together with colleagues from Forschungszentrum J¨¹lich and partner institutions, Neubauer organized the SOFT conference with more than 800 participants this year.

 

All the components in °ÄÃÅÁùºÏ²Ê¸ßÊÖ's burn chamber can essentially only be serviced by remote-controlled tools or robots. At the conference, J¨¹lich plasma researchers are presenting a new fast shutter for a spectrometer that protects the optical instruments when they are not in use for measurements, in particular during ignition when most of the contaminating particles are mobile.

 

 

Electric drives cannot be used in the burn chamber due to the strong, disturbing magnetic fields. "The shutter is additionally protected by a molybdenum screen, which reflects the thermal radiation. Together with a sophisticated combination of thermally conducting and insulating materials this maintains an acceptable temperature," says Bardawil.

 

At SOFT 2012, other J¨¹lich scientists are presenting new concepts for uniformly cooling the instrument mirrors under extreme conditions. "Large temperature differences arise on the mirror surface close to the cooling channels. With the aid of simulations, we optimized the cooling channels in order to minimize divergences," explains Andreas Krimmer, who also works in the field of fusion technology. The temperature-related high pressure of the coolant causes other deformations. At the moment, researchers are testing various elastic materials in order to even out the deformations thus ensuring that in 2020 the fusion plasma can be ignited in Cadarache.

Source: Forschungszentrum J¨¹lich