Speaker
Matteo Fontana
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1092.pdf
Fluctuations measurements in TEM and ITG dominated negative
triangularity plasmas
M. Fontana1 , L. Porte1 , O. Sauter1 , S. Coda1 , Ajay C. K.1 ,
S. Brunner1 , G. Merlo2 , A. Fasoli1 and the TCV team
1 Swiss Plasma Center-EPFL, Lausanne, 1015, Switzerland
2 University of Texas at Austin, Austin, TX 78712, United States
Past experiments on TCV have shown that fluctuations in negative triangularity discharges
are suppressed with respect to positive triangularity plasmas with comparable profiles and hea-
ting [1][2]. These past observations had been only conducted in ohmic or EC heated discharges
where Te /Ti > 1. Gyrokinetic simulations show these plasmas to be dominated by electron
driven turbulence, especially Trapped Electon Modes (TEM) [3]. If such confinement impro-
vements were retained also in low Te /Ti plasmas, where Ion Temperature Gradient (ITG) driven
turbulence is dominant, it would be particularly interesting for the design of negative triangula-
rity DEMO-like machines.
For this reason, recent experiments have exploited the versatile heating system of TCV to
investigate the effects of triangularity on transport and fluctuations in plasmas with Te /Ti ≤ 1.
Discharges with symmetric positive and negative triangularity, characterized by comparable
density and temperature profiles, have been obtained using different levels of Neutral Beam
Injector (NBI) power. The CECE diagnostic has been used to measure temperature fluctuations
in the region 0.7 < ρ < 0.85. These measurements show reduced relative fluctuations in negative
triangularity plasmas, compared to positive triangularity discharges, also in cases where NBI is
the dominant source of heating. Linear gyrokinetic simulations, performed with the GENE code,
suggest that turbulence, in these plasmas, is dominated by ITG modes.
Non-linear gyrokinetic simulations will be employed to investigate the effects of Te /Ti on
the dominant instability regime. The foreseen fluctuations levels, calculated with the use of a
synthetic diagnostic, will be compared with the experimentally measured ones.
References
[1] Zhouji Huang. Experimental study of plasma turbulence in the TCV tokamak. PhD thesis, 2017.
[2] M. Fontana, L. Porte, S. Coda, O. Sauter, and The TCV Team. The effect of triangularity on fluctuations in a
tokamak plasma. Nuclear Fusion, 58(2):024002, 2018.
[3] Gabriele Merlo. Flux-tube and global grid-based gyrokinetic simulations of plasma microturbulence and
comparisons with experimental TCV measurements. PhD thesis, EPFL, 2016.
