Speaker
Patrick Maget
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1040.pdf
Influence of stiff temperature profile on island stabilization by RF heating
Patrick Maget, Fabien Widmer, Olivier Février1 , Hinrich Lütjens2 , Xavier Garbet
CEA, IRFM, F-13108 Saint Paul-lez-Durance, France.
1 SPC, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
2 Centre de Physique Théorique, Ecole Polytechnique, CNRS, France.
Theory and experiments show that turbulent transport in tokamaks is triggered above a critical
temperature gradient, and leads to resilient (also refered to as stiff) profiles above this threshold
[1]. Inside magnetic islands, where the temperature profile is flattened, a reduced diffusivity is
expected and indeed measured [2]. The consequences of profile stiffness on island stabilization
by RF heating has recently been investigated analytically and numerically [3], using a character-
re f σ −1
istic form for heat diffusivity as χ⊥ = χ⊥ T 0 /Teq
0 , with σ the stiffness parameter and Teq
the equilibrium temperature. This formulation reproduces the low diffusivity below a threshold
in temperature gradient, and the large diffusivity above this threshold, with an actual equilib-
rium temperature gradient that lies in the turbulent transport dominated regime. We find that
the stabilization efficiency varies as (PRF /Peq )1/σ , with Peq the power injected inside the island
position and PRF the additional heat source centered at the O-point of the island. For non-stiff
profiles (σ = 1), we find a good agreement with known results [4]. In the most common case
where the ratio (PRF /Peq ) is small, the stabilization can be much larger than anticipated when
assuming non-stiff profiles. Numerical simulations with the XTOR code [5], where a RF heat
source is deposited at the O-point of a (2,1) island, shows a good agreement with the analyti-
cal model. The stabilization of Neoclassical Tearing Modes by the combined effect of heat and
current drive can then be addressed in more realistic conditions [6].
References
[1] A. M. Dimits et al., Physics of Plasmas 7, 969 (2000); X. Garbet et al., Plasma Physics
and Controlled Fusion 46, B557 (2004). F. Imbeaux et al, Plasma Physics and Controlled
Fusion 43, 1503 (2001); P. Mantica et al., Phys. Rev. Lett. 102, 175002 (2009);
[2] W. A. Hornsby et al., Physics of Plasmas 17, 092301 (2010); K. Ida et al., Phys. Rev. Lett.
109, 065001 (2012); Bardòczi et al., Physics of Plasmas, 24(12), 122503 (2017)
[3] P. Maget et al., Physics of Plasmas 25, 022514 (2018)
[4] C. C. Hegna et al., Physics of Plasmas 4, 2940 (1997); D. D. Lazzari et al., Nuclear Fusion
49, 075002 (2009).
[5] H. Lütjens and J.-F. Luciani, Journal of Computational Physics 229, 8130 (2010).
[6] F. Widmer et al., Neoclassical Island Control with Stiff Temperature Model (European
Physical Society, Prague (Czech Republic), 2018).
