TJ-II:Role of isotope effect on biasing induced transitions in the TJ-II stellarator

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Experimental campaign

2017 Spring

Proposal title

Role of isotope effect on biasing induced transitions in the TJ-II stellarator

Name and affiliation of proponent

S. Ohshima, Institute of Advanced Energy, Kyoto University, Kyoto, Japan

H. Takahashi, NIFS, Japan

Ulises Losada Ciemat, Spain

Details of contact person at LNF (if applicable)

Enter contact person here or N/A

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

Motivation: Experimental studies have shown a reduction of the L-H power threshold by about 50% when using Deuterium instead of Hydrogen in tokamaks [1]. The influence of isotope mass on spontaneous L-H transition has been recently reported in DIII-D [2] and in the TJ-II stellarator, concluding that Zonal Flows are instrumental both in H and D dominated plasmas to trigger the L-H transition [3].

Goals and planning: We propose to investigate the influence of isotope mass (H vs D) on TJ-II electrode biasing induced transitions with to goals:

  1. Study the influence of ion mass to reach biasing improved confinement regimes. If possible, biasing induced Limit cycle oscillation will be investigated to explore the dynamics of L-H transition and the difference between H vs D plasmas. This phenomenon was observed in Heliotron J biasing plasma.
  2. Study the influence of magnetic configuration (ripple / iota) on biasing induced transitions and turbulence-induced transport.

Experimental set-up: Target plasma: ECRH and NBI plasmas Configuration: comparative studies in standard configuration (e.g. 100_42) and configuration with reduced volume (e.g. 100_30). Electrode position: $ \rho \simeq 0.8 $ / Biasing ramp up/down up to 350 V Key diagnostics:
Dual Langmuir probe system (density, potential and LRC), HIBP (space potential, Er profiles fluctuation), Thomson scattering (Te, ne profiles), Doppler reflectometer (poloidal flow velocity, Er, fluctuations), ECE (Te profile), spectroscopy ($ H_\alpha $)

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

Preferred dates: (format dd-mm-yyyy)

References

  1. F. Ryter et al., Nuclear Fusion 53 (2013) 113003
  2. L. Schmitz, EX/P3-11, IAEA2016
  3. U. Losada et al., CWGM/Madrid January 2017

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