Experimental production and identification of electron temperature gradient modes

Abstract

The electron temperature gradient ͑ETG͒ mode, which is believed to be one of the strongest candidates for the anomalous electron energy transport in plasmas, is difficult to detect in experiments because of its high frequency ͑ϳMHz͒ and short wavelength ͑k Ќ e Յ 1͒. Using a dc bias heating scheme of the core plasma, we are able to produce a sufficiently strong ETG for exciting ETG modes in the Columbia linear machine ͓R. Scarmozzino, A. K. Sen, and G. A. Navratil, Phys. Fluids 31, 1773 ͑1988͔͒. A high frequency mode at ϳ2 MHz, with azimuthal wave numbers m ϳ 14-16 and parallel wave number k ʈ ϳ 0.01 cm −1 , has been observed. The frequency range is consistent with the result of a kinetic dispersion relation of slab ETG modes with appropriate E ៝ ϫ B ៝ Doppler shift. The scaling of its fluctuation level with the temperature gradient scale length and the radial structure are found to be roughly consistent with theoretical expectations. Therefore, this is one of the first direct definitive identifications of ETG modes.

Measurements of Electron Thermal Transport due to Electron Temperature Gradient Modes in a Basic Experiment

“…Although the electron scale fluctuations were identified in a tokamak experiment [14], the ETG characterization was not complete and its role in the electron transport was not directly verified. Production and identification of slab ETG mode have been successfully demonstrated in a basic experiment in Columbia Linear Machine (CLM) [15]. Using a dc bias heating scheme of the core plasma, we were able to produce sufficiently strong electron temperature gradient to excite ETG modes in CLM experiments [15], which has been recently verified partially in numerical simulation [16].…”

“…Production and identification of slab ETG mode have been successfully demonstrated in a basic experiment in Columbia Linear Machine (CLM) [15]. Using a dc bias heating scheme of the core plasma, we were able to produce sufficiently strong electron temperature gradient to excite ETG modes in CLM experiments [15], which has been recently verified partially in numerical simulation [16]. These results and our novel diagnostic technique for local measurement of electron thermal transport enabled the first determination of its direct measurement.…”

“…This is confirmed by the parallel electron energy distribution measurement. [15]. We used an especially designed miniature twin Langmuir Probes [15] for the measurement of plasma parameters.…”

“…[15]. We used an especially designed miniature twin Langmuir Probes [15] for the measurement of plasma parameters. Figure 2 shows typical radial profiles of plasma density, electron temperature and its gradient.…”

Analogous Saturation Mechanisms of the Ion and Electron Temperature Gradient Drift Wave Turbulence

“…[23,24]. CLM is steady-state collisionless cylindrical plasma machine with an uniform axial magnetic field (Fig.1).…”