TJ-II:Alfven Eigenmodes and biasing in TJ-II

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Experimental campaign

2017 Spring

Proposal title

Alfven Eigenmodes and biasing in TJ-II

Name and affiliation of proponent

A. Melnikov for HIBP group Fusion National Laboratory, CIEMAT, 28040, Madrid, Spain Institute of Plasma Physics, NSC KIPT, 310108, Kharkov, Ukraine National Research Centre ‘Kurchatov Institute’, 123182, Moscow, Russia

Details of contact person at LNF (if applicable)

A. Melnikov

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

Motivation. It has been observed during spring campaign 2016 that Alfven Eigenmodes are affected by the edge polarization (biasing) of the NBI-driven TJ-II discharge. The modulation of the specific modes with frequencies about 100 kHz was observed. Some of the modes were excited by biasing while the others were suppressed. So, biasing appears to be an external actuator to control the AEs. The search for the actuator to control the AEs is one of the important topics of the ITPA on the Energetic Particles in toroidal fusion devices.

1. Title: Biasing effect on the mean potential and Alfven Eigenmodes. Aim: to extend the database for the phenomena observed, to check the working hypothesis. a) evolution of the gaps in the Alfven continuum due to density and iota evolution induced by biasing b) deformation of the trajectories of the resonating particles by edge Er induced by biasing.

1.1. Er (potential) response to the biasing. Dependence on plasma density. TS and (r, t) profile analysis: how biasing affects (r), Ne(r), Te(r) profiles NBI low-density plasma, low frequency meander for negative and positive Ubias to measure profiles with/without biasing. No transitions to better confinement. Extension transitions to better confinement.

1.2 AE response to the biasing. AE mode location by HIBP Time traces of HIBP parameters around mode excitation/suppression location Time traces for Ipl, Halpha, Zeff, impurities, etc. Turbulence rotation VTURB, S(k,f) and ExB rotation (plasma potential profile) changes due to biasing Effect on the turbulent particle flux, ΓExB Dependence of the biasing effect on density NBI low-density plasma, triangle or high frequency meander for negative and positive Ubias to measure excitations/suppression of various AEs with/without biasing. 1.2 Study of the nature of 20 kHz mode affected by biasing

2. Study of chirping Alfven modes: from Alfvenic Zoo to the mode identification and characterization. Systematization of the individual mode characteristics: Frequency, m, n, Vpol, cross-phases between density, potential and toroidal shift and associated ΓExB Co-Counter-balanced NBI in low-density discharges To be able to focus on the specific mode - accurately reproducible discharges needed. Structure of the mode, m-s, radial size, mode rotation, S(k,f) Poloidal rotation for all quantities: density, Bpol, potential Compare plasma turbulence rotation, ExB rotation and AE rotation. Does the mode rotates with plasma? To check clearly the direction- diamagnetic ion or electron drift.

If applicable, International or National funding project or entity

Enter funding here or N/A

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation:
  • Essential diagnostic systems:
  • Type of plasmas (heating configuration):
  • 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

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