TJ-II: Influence of Alfven Eigenmodes in edge turbulence and Zonal Flows

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Experimental campaign

2021

Proposal title

TJ-II: On the coupling between fast particle Alfven modes, zonal flows and turbulence in the TJ-II stellarator

Name and affiliation of proponent

Filip Papausek, Ulises Losada, Boudewijn van Milligen, Alvaro Cappa, Marian Ochando, Enrique Ascasibar, Macerana Liniers, Carlos Hidalgo and the TJ-II team

Alexander Melnikov and the HIBP Kurchatov team

Alexander Kozachez and the HIBP Kharkov team

Jacobo Varela / UC3M

David Zarzoso and Samuel Mazzi / Aix Marseille University

Details of contact person at LNF

Filip Papausek / filip.slapina@gmail.com

Description of the activity

Fast ions have been found to impact plasma confinement. While most of previous research have been focussed on the excitation and impact of fast ions modes in plasma performance, because of the drain of energy related to fast particle losses with a concomitant potential damages in the plasma facing components, there is a growing interest on the impact on fast particles on plasma turbulence and self-organization phenomena [1] [2].

The unique TJ-II experimental set-up using a dual HIBP has shown that, in some conditions, long range correlations (LRC) are detected both at the AE frequencies and low frequencies (< 10 kHz). LRC are observed in plasma potential fluctuations but not in density fluctuations as expected in zonal flow structures [3]. Recent experiments using edge probes have shown clear evidence non-linear coupling between Alfven modes and broadband turbulence as well as some hints of coupling between low frequency Zonal Flows and broad-band turbulence using edge probes measurements [4]. These results were obtained in plasma regimes with steady-state AEs activity in a time scale of about six energy confinement times.

The goal of this proposal is to address the following questions: may fast particles driven by NBI interact with global structures in the plasma (zonal flows) and turbulence?. With this goal, the strategy of the TJ-II experimental program would be:

1. Investigation of AEs localized in the edge region by means of edge probes and HIBP [reference shot 43706] and AEs identification.

2. Influence of plasma density and magnetic configuration on AEs, turbulence and Long-Range-Correlated structures using dual Langmuir probes and HIBP measurements in plasma regimes with the best as possible density & plasma current control in NBI plasmas.

3. Non-linear coupling studies of AEs, turbulence and ZFs.

4. Influence of radial electric fields (using edge biasing) on LRC, AEs and ExB turbulent transport.

International or National funding project or entity

If applicable, enter funding here or write N/A

Description of required resources

Required resources:

• Number of plasma discharges or days of operation: 3

• Essential diagnostic systems: Dual Langmuir probe system [February, May&June] in TJ-II and HIBP [May & June]

• Type of plasmas (heating configuration): ECRH & NBI

• Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility in NBI plasmas.

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. A. Di Siena et al « Electromagnetic turbulence suppression by energetic particle driven modes” 2019 Nucl. Fusion 59 124001
  2. S. Mazzi, et al. Towards enhanced performance in fusion plasmas via turbulence suppression by MeV ions, submitted to Nature Physics
  3. C. Hidalgo et al., 28th IAEA Conf., Nice 2021
  4. Filip Papoušek et al., Physics Meeting December 14th (2020)

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