Stochasticity in fusion plasmas

[摘要] To date, the most advanced concepts for fusion confinement are the tokamak and thestellarator. The stellarator is exemplified by the Wendelstein 7-X (W7-X) stellarator, whichstarted recently operation in December 2015 in Greifswald, Germany. The tokamak schemeis currently the leading variant for plasma confinement and is therefore being used for theITER design and is planned for the DEMO reactor. However, reliably achieving and maintaining the stability of fusion plasmas remains an important fundamental issue that needs tobe resolved.In both tokamaks and stellarators, stochastic magnetic fields can arise and influence theinterplay between three-dimensional (3D) magnetic topology and plasma confinement.Stellarator devices represent an inherent 3D challenge. They make use of the island divertor concept, and stochasticity and magnetic topology therefore play a fundamental role intheir operation. With the extended operational regimes pioneered on the large helical device(LHD) and with W7-X, attention has been directed towards the challenge of 3D plasmaequlibria, transport and plasma–surface interactions.