Wendelstein 7-AS (1988 - 2002)
Research status
The Wendelstein 7-AS stellarator experiment, which was operated at IPP in Garching from 1988 till 2002, was the first test of basic elements of the stellarator optimisation.
Results
The experiment has demonstrated that the innovative modular coil system can be manufactured to the exact specifications. With plasma temperatures of 70 million degrees for the electrons and 16 million degrees for the ions, energy confinement times of up to 60 milliseconds, and reactor-grade plasma densities, Wendelstein 7-AS has broken all stellarator records in its size group.
The optimisation criteria used have also been confirmed: The troublesome displacement of the plasma column in the vessel as the plasma pressure increases – as compared with a conventional stellarator – is appreciably reduced in Wendelstein 7-AS. Its successor now being built at the Greifswald Branch Institute of IPP, the completely optimised Wendelstein 7-X device, is intended to demonstrate the reactor relevance of the new stellarators.
Wendelstein 7-AS was the first stellarator to be equipped with a divertor. Whereas previous devices restricted the outward extent of the plasma column by means of material limiters, Wendelstein 7-AS has done this contact-free since 1999 by means of magnetic fields: The plasma boundary splits – in keeping with the symmetry of the magnetic field – into individual offshoots through which energy and particles move to limited areas of the vessel wall, just like the divertor plasma in a tokamak. These areas of the wall are protected by special collector plates – ten such along the plasma column. Here the incident particles, together with the undesirable impurities from the plasma, can be neutralised and pumped off. This greatly facilitated impurity and density control; the plasma power could be sparingly distributed on the collector plates by radiation.
The device thus provided advance information for Wendelstein 7-X, which will likewise be fitted with a divertor.
Results
The experiment has demonstrated that the innovative modular coil system can be manufactured to the exact specifications. With plasma temperatures of 70 million degrees for the electrons and 16 million degrees for the ions, energy confinement times of up to 60 milliseconds, and reactor-grade plasma densities, Wendelstein 7-AS has broken all stellarator records in its size group.
The optimisation criteria used have also been confirmed: The troublesome displacement of the plasma column in the vessel as the plasma pressure increases – as compared with a conventional stellarator – is appreciably reduced in Wendelstein 7-AS. Its successor now being built at the Greifswald Branch Institute of IPP, the completely optimised Wendelstein 7-X device, is intended to demonstrate the reactor relevance of the new stellarators.
Wendelstein 7-AS was the first stellarator to be equipped with a divertor. Whereas previous devices restricted the outward extent of the plasma column by means of material limiters, Wendelstein 7-AS has done this contact-free since 1999 by means of magnetic fields: The plasma boundary splits – in keeping with the symmetry of the magnetic field – into individual offshoots through which energy and particles move to limited areas of the vessel wall, just like the divertor plasma in a tokamak. These areas of the wall are protected by special collector plates – ten such along the plasma column. Here the incident particles, together with the undesirable impurities from the plasma, can be neutralised and pumped off. This greatly facilitated impurity and density control; the plasma power could be sparingly distributed on the collector plates by radiation.
The device thus provided advance information for Wendelstein 7-X, which will likewise be fitted with a divertor.
Scetch of the Wendelstein 7-AS fusion device
Wendelstein 7-AS
Construction of Wendelstein 7-AS
Construction of Wendelstein 7-AS
[ Last Update 03.11.2009 | Responsible | Sitemap | IPP-Home | Disclaimer ]