Abstract
Additional electron cyclotron resonance heating (ECRH) is used in an ion-temperature-gradient instability dominated regime to increase R/LTe in order to approach the trapped-electron-mode instability regime. The radial ECRH deposition location determines to a large degree the effect on R/LTe. Accompanying scale-selective turbulence measurements at perpendicular wavenumbers between k⊥ = 4–18 cm−1 (k⊥ρs = 0.7–4.2) show a pronounced increase of large-scale density fluctuations close to the ECRH radial deposition location at mid-radius, along with a reduction in phase velocity of large-scale density fluctuations. Measurements are compared with results from linear and non-linear flux-matched gyrokinetic (GK) simulations with the gyrokinetic code GENE. Linear GK simulations show a reduction of phase velocity, indicating a pronounced change in the character of the dominant instability. Comparing measurement and non-linear GK simulation, as a central result, agreement is obtained in the shape of radial turbulence level profiles. However, the turbulence intensity is increasing with additional heating in the experiment, while gyrokinetic simulations show a decrease.
Highlights
The efficiency of a future fusion experiment such as ITER or DEMO will be determined largely by two factors: its susceptibility to magnetohydrodynamic (MHD) instabilities and the transport caused by microturbulence [1]
The design scenario for ITER operation is based on MHD stability and good confinement provided by the H-mode [2, 3]
Particular interest is attributed to the reaction of the fluctuations as the turbulence is modified from the ion temperature gradient modes (ITG) towards the trapped-electron-mode instability (TEM) regime, which is achieved by applying additional electron cyclotron resonance heating (ECRH) at mid-radius
Summary
The efficiency of a future fusion experiment such as ITER or DEMO will be determined largely by two factors: its susceptibility to magnetohydrodynamic (MHD) instabilities and the transport caused by microturbulence [1]. Particular interest is attributed to the reaction of the fluctuations as the turbulence is modified from the ITG towards the TEM regime, which is achieved by applying additional electron cyclotron resonance heating (ECRH) at mid-radius. In this context it has to be noted that the acronyms ITG and TEM are widely used in literature to distinguish between the two modes, there is no clear boundary where ITG disappears and TEM is excited or vice versa (except for obvious cases like switching off the ITG by using ∇Ti = 0 in simulations, for example).
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