High density operation close to the Greenwald limit and H-mode limit in ASDEX Upgrade
The L-mode and H-mode density operational window in the vicinity of the density limit has been investigated with a combination of gas puff refuelling and improved fine tuning of neutral beam injection (NBI) heating power. In this way, a novel strategy is achieved by means of a parallel increase of density and heating power. As the density limit is approached, H-modes degrade into L-modes independently of heating power; this is in contrast to the generally accepted L -> H mode threshold scaling. Furthermore, contrary to the well known heating power independent Greenwald limit, the L-mode density limit increases moderately with rising heating power, if a simple power law is assumed. The power dependence becomes more obvious when analysed in terms of edge densities and powers flowing across the separatrix into the scrape-off layer. The corresponding H-mode studies show that before an H-mode quenches into an L-mode the maximum achievable density (ie the H-mode density limit) is practically independent of the heating power, as observed on many machines.
Bibliographic Reference: Article: Nuclear Fusion, Vol. 37 (1997) No. 11, pp. 1607-1614
Record Number: 199810149 / Last updated on: 1998-02-12
Original language: en
Available languages: en