Magnetic Field at Wendelstein 7-X is spot on!
The magnetic field of Wendelstein 7-X is spot on! Tests have been performed which show that the complex coils do produce the required magnetic field of which the configuration is in line with the calculations of the physicists. This is a big milestone in the operational preparations that are currently under way. Wendelstein 7-X should produce its first plasma later this year.
A precise magnetic field is required to confine the high-temperature fusion plasma, since it keeps the hot ions and electrons away from the walls of the plasma vessel. The field lines in the centre of the circular plasma vessel must span closed, nested circular sufraces. If not, the outward pointing field lines will direct plasma particles against the walls, which would make it impossible to achieve a high temperature plasma.
The diagnostic used to measure the magnetic surfaces creates beautiful images. Click the link below for high-quality images of the flux surfaces.
The flux surface diagnostic enables the measurement of the structure of the field with high precision. A thin electron beam is injected and moves along a field line in circular tracks through the evacuated plasma vessel. Along its path, it leaves behind a tracer which is caused by the collisions of the electrons with residual gas in the vessel. By now moving a fluorescent rod through the vessel cross section, light spots are created when the electron beam hits the rod. This way the entire cross section of the magnetic field gradually becomes visible.
During one measurement, which lasts around 60 seconds, the electron beam covers a distance of several kilometres and circulates the plasma vessel many times. The image forms from the light points on the rod. The nested flux surfaces are shown in dotted lines.