Turbulence simulations of transport barrier relaxations in tokamak edge plasmas
A promising operational regime of future fusion reactors is characterized by an edge transport barrier, i.e. a localized steepening of density and temperature gradients. Typically, such a barrier is unstable and relaxes quasi-periodically. In this work, we show that complete barrier relaxation cycles can be reproduced by three-dimensional turbulence simulations. In these simulations, a barrier forms due to an imposed E x B shear flow. This barrier relaxes intermittently on the confinement time scale, even if fluctuations of the E x B flow are suppressed. It is found here that if the E x B shear increases faster than linearly with heating power, the relaxation frequency decreases with power. A relaxation event has a complex dynamical behaviour, characterized by the intermittent growth of a mode at the barrier centre. A crucial ingredient in this non-linear dynamics is a time delay for an effective E x B velocity shear stabilization.
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion 49 (2007), pp. 507-523
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/10.1088/0741-3335/49/4/013
Record Number: 200719145 / Last updated on: 2007-04-11
Original language: en
Available languages: en