Comparison of electrostatic and electromagnetic synchronization of drift waves and suppression of drift wave turbulence in a linear device

Abstract

Abstract. Experiments in a cylindrical magnetized plasma on the control of drift waves by means of two different spatiotemporal open-loop control systems -an electrostatic and an electromagnetic exciter -are reported. The drift wave dynamics is controlled by a mode-selective signal created with azimuthal arrangements of eight electrodes and eight saddle coils, respectively. Nonlinear interaction between the control signals and drift waves is observed, leading to synchronization of coherent drift waves and suppression of broadband drift wave turbulence. The cross-phase between density and potential fluctuations reduces from ≈ π/2 in turbulence to ≈ 0 in controlled turbulence. Hence, the cross-field transport is reduced to the level of coherent drift waves. For both control systems the coupling to the drift wave can be ascribed to the drive of parallel currents, on the one hand via direct electric contact and on the other hand via electromagnetic induction.

External excitation of a short-wavelength fluctuation in the Alcator C-Mod edge plasma and its relationship to the quasi-coherent mode

“…The guided behavior is reminiscent of resonance cones predicted for low-frequency electrostatic waves [51][52][53][54][55] , as well as shear Alfvén waves 34 , but these scenarios are not consistent with the high collisionality (τ −1 ei /ω ≈ 20 ≫ 1) of the edge, nor the driven resonance around the QCM. Experiments in linear devices have shown that exciting mode-selective parallel currents is the essential ingredient for coupling to drift waves, and that this may be done inductively 33 .…”

“…However, in experiments examining nonlinear interaction between a driven mode and a coherent drift wave structure on a linear device, Brandt et al 33 observed frequency pulling and the appearance of sidebands in the fluctuation spectra. These features are not apparent in the fluctuation spectra obtained during Shoelace antenna operation, though higher antenna power may be needed to access this behavior.…”

Network approach to the pinning control of drift-wave turbulence

“…Drift-wave turbulence is generally believed to be responsible for the anomalous crossfield particle transport [23], and its control and suppression therefore is of great importance to the performance of magnetic confinement fusion devices, e.g., the tokamaks [24]. Over * Corresponding author: wangxg@snnu.edu.cn the past two decades, there have been continuous attempts in extending the techniques developed in chaos control to the suppression of drift-wave turbulence, in which a variety of theories and techniques have been proposed [25][26][27][28][29][30][31][32]. In the regime of weak turbulence, by use of the technique of timedelay autosynchronization (TDAS) [33], it has been shown by a series of studies that the chaotic temporal behavior of the drift waves in cylindrical magnetized plasmas can be tamed to be periodic [25,27,31].…”

“…In the regime of weak turbulence, by use of the technique of timedelay autosynchronization (TDAS) [33], it has been shown by a series of studies that the chaotic temporal behavior of the drift waves in cylindrical magnetized plasmas can be tamed to be periodic [25,27,31]. Moreover, by the strategy of open-loop synchronization, namely the mode-selective control, it has been shown recently that the complicated spatial behavior of the weakly developed drift-wave turbulence can be also successfully controlled (synchronized) to a predefined pattern of regular spatial structure [29,30]. More recently, by use of the method of pinning coupling, it has been shown that both the spatial and temporal behaviors of the drift-wave turbulence can be efficiently regulated into different spatiotemporal patterns, given the pinning strength is larger to some critical value [34].…”

Transport barrier for the radial diffusion due to theE×Bdrift motion of guiding centers in cylindrical confinement geometry

“…In that way it is possible to have a very accurate description of the space time behavior of the plasma [10,11,7]. In addition it is worth noticing that it is also possible to act on the plasma using electrodes directly in contact with the plasma, producing for example a mode locking between the injected sinusoidal signal and the plasma dynamics [12,13]. Moreover, in the SOL region of tokamaks where the field lines are connected to the wall, a parallel current created by probes acts on perpendicular dynamics [14].…”