Nonlinear interaction of drift waves with driven plasma currents

Brandt, C.; Grulke, O.; Klinger, T.

doi:10.1063/1.3328820

Cited by 14 publications

(7 citation statements)

References 25 publications

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“…The broadening of the range over which the instability is controlled as the beat-wave power is increased is indicated by this contour. Similar observations are made in VINETA [26], where the effect was compared to "Arnold Tongues" seen in nonlinearly driven unstable oscillators [27,28]. The exact mechanism by which the beating SAWs couple nonlinearly to and control the unstable mode is still under investigation.…”

supporting

confidence: 57%

Control of Gradient-Driven Instabilities Using Shear Alfvén Beat Waves

et al. 2010

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A new technique for manipulation and control of gradient-driven instabilities through nonlinear interaction with Alfvén waves in a laboratory plasma is presented. A narrow, field-aligned density depletion is created in the Large Plasma Device (LAPD), resulting in coherent, unstable fluctuations on the periphery of the depletion. Two independent shear Alfvén waves are launched along the depletion at separate frequencies, creating a nonlinear beat-wave response at or near the frequency of the original instability. When the beat-wave has sufficient amplitude, the original unstable mode is suppressed, leaving only the beat-wave response, generally at lower amplitude.PACS numbers: 52.35. Bj, 52.35.Mw, 52.35.Qz In magnetized plasmas in the laboratory, the loss of heat, particles, and momentum across the confining magnetic field is predominantly caused by turbulent transport associated with pressure-gradient-driven instabilities [1,2]. Controlling these instabilities to mitigate the transport they produce is therefore highly desirable for magnetic confinement fusion devices such as tokamaks. Direct control of gradient-driven instabilities has been achieved using arrays of electrodes or external saddle coils to induce fluctuating parallel currents in a cylindrical plasma device [3,4]. In these experiments, when the excited electric fields matched the frequency and wavenumber of a drift-wave mode in the device the observed turbulent spectrum collapsed onto the single coherent driven mode (synchronization) and turbulent transport is reduced [5]. Extending the transport control enabled through mode-synchronization to high-temperature fusion devices is highly desirable but it would not be possible using material electrodes. It is also not clear whether saddle coils would be effective at driving currents for synchronization in a high-performance device.Turbulence control with core plasma access might be achieved using externally-launched radiofrequency (RF) waves. High-power RF is expected to be an important tool for heating and current drive on next-step fusion experiments such as ITER [6] and could be available for application to turbulence and transport control. Creation of flow shear for turbulence suppression [7] using RF waves has been theorized [8] and recently demonstrated in the Alcator C-Mod tokamak [9,10]. Direct modification of gradient-driven instabilities is also possible through interaction with an RF field. Control of driftwave fluctuations was demonstrated in Q-machine experiments using lower hybrid waves to affect plasma properties and the drift-wave dispersion to suppress growth [11][12][13][14]. The modification of other transport related instabilities, such as the ion temperature gradient (ITG) instability, in the presence of RF driven fast magnetosonic waves has also been suggested and investigated theoretically [15]. This Letter reports on novel laboratory experiments using RF waves, in particular shear Alfvén waves (SAWs), to modify gradient-driven instabilities. Two copropagating SAWs with slightl...

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confidence: 57%

Control of Gradient-Driven Instabilities Using Shear Alfvén Beat Waves

et al. 2010

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“…This is an important condition, which differentiates our control experiments from previous ones, where almost the whole plasma volume was affected by equally distributed active electrodes [2,3].…”

Section: Methodsmentioning

confidence: 93%

“…For example, it has been shown in a linear machine that by driving one of the drift wave modes present in the plasma the background turbulence level can be reduced [2]. More recently, also the nonlinear interaction of drift waves with externally driven currents has been investigated [3]. The synchronization of dust acoustic waves in a dusty plasma has been also successfully achieved using a negatively biased driving electrode [4].…”

Section: Introductionmentioning

confidence: 99%

Spatiotemporal synchronization of drift waves in a magnetron sputtering plasma

Martines¹,

Zuin²,

Cavazzana³

et al. 2014

Physics of Plasmas

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A feedforward scheme is applied for drift waves control in a magnetized magnetron sputtering plasma. A system of driven electrodes collecting electron current in a limited region of the explored plasma is used to interact with unstable drift waves. Drift waves actually appear as electrostatic modes characterized by discrete wavelengths of the order of few centimeters and frequencies of about 100 kHz. The effect of external quasi-periodic, both in time and space, travelling perturbations is studied. Particular emphasis is given to the role played by the phase relation between the natural and the imposed fluctuations. It is observed that it is possible by means of localized electrodes, collecting currents which are negligible with respect to those flowing in the plasma, to transfer energy to one single mode and to reduce that associated to the others. Due to the weakness of the external action, only partial control has been achieved.

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“…Those studies were extended in the VINETA device, where direct drift wave excitation and synchronization was achieved using parallel currents driven by electrode arrays and saddle coils. 6 Synchronization in VINETA can lead to a reduction in cross-field particle transport associated with drift waves. 7 This article expands on previously reported 8 laboratory experiments using nonlinearly driven beat waves driven by shear Alfvén waves (SAWs) to interact with and control GDIs.…”

Section: Introductionmentioning

confidence: 99%

Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

et al. 2011

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The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10% of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.

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Nonlinear interaction of drift waves with driven plasma currents

Cited by 14 publications

References 25 publications

Control of Gradient-Driven Instabilities Using Shear Alfvén Beat Waves

Control of Gradient-Driven Instabilities Using Shear Alfvén Beat Waves

Spatiotemporal synchronization of drift waves in a magnetron sputtering plasma

Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

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