TJ-II: Biasing experiments in TJ-II: Feed back control of Zonal Flows and cross-phase effects on turbulent transport

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Experimental campaign

2021

Proposal title

TJ-II: Biasing experiments in TJ-II: Feed back control of Zonal Flows and cross-phase effects on turbulent transport

Name and affiliation of proponent

NIFS [H. Takahashi]

KYOTO UNIVERSITY [Sh. Ohshima]

CIEMAT [U. Losada,I. Voldiner, B. van Milligen, C. Hidalgo]

Details of contact person at LNF

If applicable, enter contact person here or write N/A

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 [1]. 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 [2] or / and by cross-phase effects [3]. 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 [4]. 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.

International or National funding project or entity

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Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 days of operation
  • Essential diagnostic systems: Edge biasing and edge probes
  • Type of plasmas (heating configuration): ECRH & NBI
  • Specific requirements on wall conditioning if any:
  • External users: need a local computer account for data access: yes/no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. R. Gerrú et al., Nucl. Fusion 59 106054 (2019)
  2. H. Biglari et al., Phys of Fluid 2, 1 (1990)
  3. P. W. Terry et al., , Phys. Rev. Lett. 87, 185001 (2001)
  4. Ch-B Kim et al., Sci Rep. 8: 8622 (2018)

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