Background, motivation, concept and scientific aims for building a dynamic ergodic divertor

The dynamic ergodic divertor is a new concept for distributing the power flux from the plasma to a large area target plate while keeping or even improving the particle removal capabilities of the toroidal pump limiter ALT-II. The transport in the ergodized boundary magnetic field shields the impurities from penetrating into the central plasma while the option of a radiative mantle should become even more efficient. To achieve the ergodization, a set of perturbation coils is oriented parallel to the field lines of a resonant layer (ri = 3 layer). A four phase perturbation current (up to 15 kA) is selected to impose the option of field rotation; the available frequencies are DC, 50 Wt and the band between 1 and 10 kHz. The low frequency option is chosen for smearing out the divertor strike point while the rotation high frequency option may give rise to a 'temporal' ergodization in addition to the spatial one and may improve the plasma confinement and increase the disruption limit. (C) 1997 Elsevier Science S.A.