Simulation of internal transport barriers by means of the canonical profile transport model
- Russian Research Centre Kurchatov Institute, Nuclear Fusion Institute (Russian Federation)
- Culham Science Centre, EURATOM/UKAEA Fusion Association (United Kingdom)
Models with critical gradients are widely used to describe energy balance in L-mode discharges. The so-called first critical gradient can be found from the canonical temperature profile. Here, it is suggested that discharge regimes with transport barriers can be described based on the idea of the second critical gradient. If, in a certain plasma region, the pressure gradient exceeds the second critical gradient, then the plasma bifurcates into a new state and a transport barrier forms in this region. This idea was implemented in a modified canonical profile transport model that makes it possible to describe the energy and particle balance in tokamak plasmas with arbitrary cross sections and aspect ratios. The magnitude of the second critical gradient was chosen by comparing the results calculated for several tokamak discharges with the experimental data. It is found that the second critical gradient is related to the magnetic shear s. The criterion of the transport barrier formation has the form (a{sup 2}/r)d/drln(p/p{sub c}) > z{sub 0}(r), where r is the radial coordinate, a is the plasma minor radius, p is the plasma pressure, p{sub c} is the canonical pressure profile, and the dimensionless function z{sub O}(r) = C{sub O} + C{sub 1}s (with C{sub 0i} {approx}1, C{sub 0e} {approx}3, and C{sub 1i,e} {approx}2) describes the difference between the first and second critical gradients. Simulations show that this criterion is close to that obtained experimentally in JET. The model constructed here is used to simulate internal transport barriers in the JET, TFTR, DIII-D, and MAST tokamaks. The possible dependence of the second critical gradient on the plasma parameters is discussed.
- OSTI ID:
- 21080655
- Journal Information:
- Plasma Physics Reports, Vol. 32, Issue 1; Other Information: DOI: 10.1134/S1063780X06010016; Copyright (c) 2006 Nauka/Interperiodica; Article Copyright (c) 2006 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-780X
- Country of Publication:
- United States
- Language:
- English
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