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Acceleration Grids for NBI

For the heating of plasma in fusion reactors different heating systems are used. The component that is introduced here is a piece of the neutralinjectionheater which bombards the torusplasma and heats up the highenergetic, neutralized protons and deuterons.

The ion-acceleration system’s heart is a set of extraction grids (3 degrees) that suck (extract) plasma out of the plasma source by creating electrical potentials and therefore they accelerate it.

The entire ionray (size 230 x 500 mm) consists of 774 single rays that are focused on one mutual point in 6,5 m. This can only be realised through geometric disposal and highest precision of the extractiondrillings.

To be able to get through the torus’ magnetic fields the plasmaray passes a neutralisor where the fast ions carry off electrons from the static neutral gas (H2) while passing by. This newly originated “neutralbeam” is able to enter the very depths of the torus to emit its energy there.

Grids that are built in this manner are used in fusionexperiments of Asdex Upgrade (IPP-Garching), TEXTOR (Researchcentre Jülich) as well as W7X (IPP-Graching Greifswald). Because, however, a lot of protons hit the surface of the copper structures those have to be cooled in a very intensive manner.


Engineering data

– Ionbeamenergy 55keV with a Ionflow of 85 A makes a beamperformance of about 4,5 MW (hydrogen-powered)
– (to be cooled) power dissipation on plasmagrid: 250 KW
– Water pressure 16 bar.

Those grids are crafted using a method that is descriped on our catalogue page “variable cooling structures”. They are our leading-edge product on this sector.

The completed component underlies very high requirements of precision and stability. The requested DIN positiontolerance of the 387 drills of 0,04 mm are close to the processtolerance of modern milling centres and the test pressure of 17 bar almost reached the load-carrying capacity limit of the copper structure.

A leakage rate of more that 10-8 mbar xl/s at a pressure of 16 bar has to be garanted for the cooling sytsem. Despite such requirements GT has already produced more than 300 grid halves like that without getting in much trouble. We also developed prototypes for the acceleration of negative ions in colaboration with IPP-Garching.

Those have additional coolingcanals and magnetcanals as well as electron traps integrated into the grid structure.