TJ-II:Blobs vs streamers

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Experimental campaign

2018 Spring

Proposal title

Blobs vs streamers

Name and affiliation of proponent

G. Grenfell, B.Ph. van Milligen

Details of contact person at LNF (if applicable)

B.Ph. van Milligen

Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)

According to a recent suggestion by Chang[1], turbulence in the edge can be of 'blob type' or 'streamer type'. Chang states: ‘A weak mean $ E × B $ shear, due to the small $ \rho_i/L $ effect, allows the formation of the streamer type turbulence.’

We propose studying this effect, not by varying $ B $, but rather by varying $ E $. To do so, we will scan the edge $ E_r $ from negative to positive (crossing zero), either by biasing or by varying the mean density near the spontaneous transition value ($ n_e \simeq 0.6 ⋅ 10^{19} $). Near zero Er, transport across the LCFS should be more streamer-like.

Measurements to make: In this scan, we will measure: Isat decay length in SOL (if possible - this may require several discharges), and $ \omega_S $.[2]

We will also attempt to quantify 'blobbiness', in order to detect the transition between 'blob-type' and 'streamer-type' turbulence. This difference might also be reflected in the radial correlation length (or causality, cf. Transfer Entropy). Perhaps there are other ways to quantify the difference between 'blob-type' and 'streamer-type' turbulence.

If applicable, International or National funding project or entity

N/A

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: at least 1 day
  • Essential diagnostic systems: Langmuir probe (2-dimensional), biasing probe
  • Type of plasmas (heating configuration): ECRH
  • Specific requirements on wall conditioning if any: N/A
  • External users: need a local computer account for data access: no
  • Any external equipment to be integrated? Provide description and integration needs: N/A

Preferred dates and degree of flexibility

Preferred dates: N/A

References

  1. C. Chang et al., Self-organization between the neoclassical and turbulent transports across the separatrix surface, resulting in the regulation of the divertor heat-load width, Synopsis for IAEA Conference (2018)
  2. P. Manz, T. Ribeiro, B. Scott, G. Birkenmeier, D. Carralero, G. Fuchert, S. Müller, H. Müller, U. Stroth, and E. Wolfrum. Origin and turbulence spreading of plasma blobs. Phys. Plasmas, 22:022308, 2015

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