TJ-II: Edge – SOL coupling studies using fast cameras and Langmuir probes: role of edge turbulence and radial electric fields

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Experimental campaign

2021

Proposal title

TJ-II: Edge – SOL coupling studies using fast cameras and Langmuir probes: role of edge turbulence and radial electric fields

Name and affiliation of proponent

Igor Voldiner, Eduardo de la Cal, Ulises Losada, Boudewijn van Milligen, Enrique Ascasibar, Carlos Hidalgo and the TJ-II team

Details of contact person at LNF

Igor Voldiner / igor.voldiner@ciemat.es

Eduardo de la Cal / e.delacal@ciemat.es

Description of the activity

Global plasma confinement studies in both ECRH [1] and NBI [2] plasmas in TJ-II have shown an improvement with density and degradation with heating power [in agreement with the results reported in the present paper. Whether the transition to improve confinement in the passage from ECRH to NBI plasma scenarios is due to the reduction of broadband turbulence or/and the modification in mean radial electric fields and low frequency ZFs structures [3] remains an open question.

In addition, previous studies have addressed the impact of edge radial electric fields (Er) on turbulence propagation and the coupling between the plasma edge and the scrape-off layer (SOL) during electron–ion root transitions where Er is changed in a controlled manner from positive to negative values [4]. It has been shown that Er does not only affects the radial turbulence correlation length but it is also capable of reducing the propagation of turbulence from the edge into the SOL. So far, edge-SOL coupling has been investigated using edge Langmuir probes. This characterization can be highly improved using the fast cameras in operation in TJ-II [5] and, in a later phase, using an active He gas puffing experimental set-up under development in TJ-II. A research programme is proposed with two goals:

1) To study the impact of edge turbulence & radial electric fields on the SOL parameters using fast cameras and edge probe.

2) To compare ECRH and NBI scenarios with similar plasma density, heating power and comparable mean (neoclassical) radial electric fields. This operational window exists in TJ-II [0.8 x 1019 – 1.1 x 1019 m-3].

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: Fast cameras and Dual Langmuir probe system in TJ-II.

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

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

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. E. Ascasibar et al., Plasma Phys. Control. Fusion 44 (2020) B307
  2. E. Ascasibar et al., Contrib. Plasma Physics 50 (2010) 594
  3. U. Losada et al., PPCF submitted (2020)
  4. G. Grenfell et al., Nucl. Fusion 60 (2020) 014001
  5. S. Zweben et al., Rev. Sci. Instrum. 88 041101 (2017)

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