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TJ-II: Biasing experiments in TJ-II: Feed back control of Zonal Flows and cross-phase effects on turbulent transport: Difference between revisions
TJ-II: Biasing experiments in TJ-II: Feed back control of Zonal Flows and cross-phase effects on turbulent transport (view source)
Revision as of 12:37, 31 January 2021
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== Description of the activity == | == Description of the activity == | ||
Stellarator devices have pioneered the detection of long-range correlations, consistent with the theory of zonal flows i.e., stable modes that are driven by turbulence and regulate turbulent transport, of interest in astrophysics, atmospheric dynamics and fusion plasmas. Results in the TJ-II stellarator indicate that both turbulent and neo-classical mechanisms, and their mutual interaction, should be considered to achieve a full understanding of the impact of radial electric fields on the mechanisms for the production and suppression of edge Zonal Flows <ref>R. Gerrú et al., Nucl. Fusion 59 106054 (2019)</ref>. Therefore the radial electric field is a key ingredient to control the turbulent drive of zonal flows [i.e. symmetry breaking of turbulence] and the damping [i.e. influence on particle orbits]. | |||
Radial electric fields can influence the turbulent transport by energy redistribution mechanisms <ref>H. Biglari et al., Phys of Fluid 2, 1 (1990)</ref> or / and by cross-phase effects <ref>P. W. Terry et al., , Phys. Rev. Lett. 87, 185001 (2001) </ref>. The influence of Er on the level of fluctuations has been investigated since the beginning of 90´s but its role on the cross-phase is still an open issue in the high temperature plasmas <ref>Ch-B Kim et al., Sci Rep. 8: 8622 (2018)</ref>. Dissipation parallel to the magnetic field creates a time delay between the plasma potential & temperature and density fluctuations. As a result the potential & temperature perturbations are phase shifted relative to the density fluctuations [non-adiabatic response]. Different mechanisms should be considered including: a) Electron–ion Coulomb collisions, b) Wave–particle interactions, c) Collisions of passing particles with trapped particles, d) Role of atomic physics via neutrals. | |||
The goal of this proposal is twofold: | |||
1)To explore the feasibility of active control of dynamical Zonal Flows by active feed-back experiments using biasing induced electric fields as external actuator and the amplitude of low frequency ZFs as sensor. | |||
2)To investigate the influence of edge biasing in the cross-phase of potential and density fluctuations. | |||
Enter description here <ref>A. Einstein, Journal of Exceptional Results (2017)</ref>, including motivation/objectives and experience of the proponent (typically one-two pages) | Enter description here <ref>A. Einstein, Journal of Exceptional Results (2017)</ref>, including motivation/objectives and experience of the proponent (typically one-two pages) | ||