ELM driven divertor target currents on TCV
There is currently both considerable interest in the physics of ELM transport in the scrape-off layer (SOL) and concern over the impact of the ELM power and particle loads on the divertor targets of future fusion reactors. This contribution describes some experimental observations of the reaction of target floating potentials and currents during ELMs in TCV, relying principally on fast measurements of these parameters using tile embedded Langmuir probe arrays. Clear evidence is presented for rapid modifications in the local target floating potentials occurring long before the characteristic rise of hydrogenic excitation emission due to local recycling provoked by the arrival at the target of the ELM ion flux. This precursor activity appears to be synchronous with the growth of MHD modes in the main chamber. Simple conditional averaging is used to derive a "coherent ELM" and thus generate the radial distribution of the current to probes held at target potential. At some locations, the coherent ELM can also be used to estimate the time evolution of the local target electron temperature, density and power flux, even though these quantities are not directly measured. The time delays between the reactions of currents, floating potentials and derived temperature are consistent with the expectations of recently published kinetic simulations of ELM energy transport down a 1D scrape-off layer plasma. The strong potential variations observed during the ELM are the result of current flows at the targets. �
Bibliographic Reference: EPFL Internal report LRP 744/03, January 2003. 57pp.
Availability: Available free of charge from: École Polytechnique Fédérale de Lausanne (EPFL), Ecublens, CH-1015 Lausanne Fax +41-21-6934747
ISBN: ISSN: 0458-5895
Record Number: 200315921 / Last updated on: 2003-02-19
Original language: en
Available languages: en