Experimental study of density pump-out effect with on-axis electron cyclotron resonance heating at the T-10 tokamak

Abstract

The results of T-10 experiments on the 'density pump-out' effect research, i.e. the escape of particles from the zone of on-axis electron cyclotron resonance heating (ECRH) to the plasma periphery are presented. The dependences of the pump-out on the central chord line-averaged plasma density n, total plasma current and the ECRH power were found. The influence of the gas influx intensity and the conditions of the chamber wall and limiter on the above-mentioned effect is also investigated. It is shown that this effect increases with the growth of the n up to a certain critical value n cr , after which the escape of particles from the zone of on-axis ECRH decreases. This critical density n cr increases with the increase of the total plasma current and the ECRH power.

Extension of the operating space of high-b N fully non-inductive scenarios on TCV using neutral beam injection

“…2 on the right. Panel b) of this figure shows the time evolution of the EC (magenta) and NB (green) power, together with the measured (blue) and the modelled (cyan) loop voltage, which clearly increases after t = 1.2 s. The electron temperature and density profiles from the Thomson Scattering diagnostic before (t = 1 s, solid line) and after (t = 1.5 s, dashed line) the NBI, which are reported in panels c-d), shows that the core plasma density is pumped-out during ECRH [10] (see also Fig. 1 a)), while it is fuelled during NBI (up to 30% at constant gas injection).…”

Anomalous absorption in ECRH experiments due to the parametric low-threshold excitation of localized UH waves

“…Thereby, the meaningful solution of (9) is an intermediate asymptotic dependence valid at the time much less than the transition time of the daughter waves through the 2D box. We assume the initial thermal noise level (12)…”

“…This can make the power deposition profile much wider than it is predicted by the linear theory and can create an illusion of the fast electron energy redistribution. In other words, this nonlinear absorption mechanism can be responsible, at least partly, for the so-called nonlocal electron transport in the on-axis X2-mode ECRH experiments at T-10 and LHD [12,13]. We can also estimate the pump power fraction absorbed by the daughter IB waves as .…”

“…The parametric decay instabilities (PDIs), which can accompany the ECRH experiments, are believed to be deeply suppressed by the huge energy loss of daughter waves from the decay region, according to the predictions of theory developed in 80 th [1]. However, during the last decade numerous ECRH experiments performed at TEXTOR, TCV, TJ-II, ASDEX-UG, LHD, T-10 and FTU [2][3][4][5][6][7][8][9][10][11][12][13] have demonstrated excitation of the anomalous phenomena. The clearest evidence of the nonlinear phenomena excitation was obtained at TEXTOR [2,3] where the strong backscattering signals down-shifted in frequency and amplitude modulated at the frequency of magnetic island were observed.…”

Plasma Electric Potential and Geodesic Acoustic Mode Evolution in Ohmic and Ecrh Regimes With Pulsed Impurity Puffing on the T-10 Tokamak

“…При включении ЭЦРН вырастают электронная и периферийная ионная температуры, а также энергосодержание в плазме. При этом падает среднехордовая плотность, измеренная вдоль центральной хорды, в соответствии с известным эффектом откачки плотности (density pump-out) [8]. В рассматриваемых режимах во время работы гиротрона на 700 мс начинается кратковременный напуск гелия.…”