Abstract Details
Abstracts
Author: Oliver Beeke
Requested Type: Poster
Submitted: 2019-02-22 05:47:32
Co-authors: M. Barnes, M. Romanelli
Contact Info:
University of Oxford
Rudolf Peierls Centre For Theo
Oxford, 00000
United Kingdom
Abstract Text:
The shaping of tokamak plasmas is known to affect the properties of micro instabilities that cause outwards radial transport of heat and particles. In particular, the elongation κ has been observed to have a stabilizing effect on the ion-temperature-gradient (ITG) instability, whilst increased triangularity can have varying effects on confinement [1-3]. It is therefore pertinent to understand the physics of shaping the plasma in order to maximize tokamak performance.
Here we use the local δf-gyrokinetic code GS2 [4] to extend an earlier modelling study [5] of the tokamak JT-60SA and advise on the ideal plasma shaping parameters for the machine in two different scenarios - one low (1.4%) β and one high (3.7%) β plasma equilibrium. We observe from electrostatic simulations that the low-beta plasma exhibits monotonic stabilization with increasing elongation, whilst the effect of triangularity varies with κ (destabilizing and stabilizing at low and high κ, respectively). However, in simulations of the high-beta plasma we observe that moderate increases in elongation (up to κ~1.4) have a destabilizing effect; beyond this elongation is again stabilizing.
To explain this phenomenon, we use a simplified Miller parametrization for the poloidal cross section to determine how an interaction between β' and κ is responsible for the observation. In particular, increasing κ at large β' increases the local magnetic shear (destabilizing) but also the perpendicular wavenumber (stabilizing). The competition between these two effects leads to the observed peak in maximum growth rates as a function of κ. We also present results from electromagnetic simulations for the high-beta equilibrium.
[1] H. Weisen et al., Nucl. Fusion 37 (1997), 1741
[2] Y. Camenen et al., Nucl. Fusion 47 (2007), 510
[3] J. Ball et al., Nucl. Fusion 58 (2018), 026003
[4] M. Kotschenreuther et al., Comp. Phys. Comm. 88 (1995), 128
[5] M. Nakata et al., Plasma Fusion Res. 9 (2014), 1403029
Comments:
