Problems related to ignition in the Next Step tokamak
A lot of work has been devoted to the scaling of Next Step tokamaks designed to reach ignition. Generally, for given assumptions about the plasma purity and profiles, the working point (i.e the central density and temperature) can be found where the required confinement time is minimum. Here the working point is assumed and the possibility of ignition of a given device is discussed; because of the analytical form of the confinement scaling, it appears that the conclusion depends only weakly on the assumption about the working point but strongly on the volume of the device and on the plasma "quality", symbolised by three factors (purity, profiles, confinement). An analytical criterion is presented which allows an easy estimate of the balance between technical and physical constraints. In an ignited plasma the fuel is mainly heated by collisions with electrons. This fact is not taken into account in a one-fluid model. A two-fluid model is presented with which the impact of the energy equipartition constraint on a tokamak scaling can be estimated. These models are used to evaluate the ignition capability of ITER. In conclusion, suggestions are made to increase the safety margin for ignition.
Bibliographic Reference: Report: EUR-CEA-FC-1418 EN (1991) 23 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199110891 / Last updated on: 1994-12-02
Original language: en
Available languages: en