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

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

Details of contact person at LNF (if applicable)

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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 . The influence of isotope mass on spontaneous L-H transition has been recently investigated in the TJ-II stellarator, concluding that Zonal Flows are instrumental both in H and D dominated plasmas to trigger the L-H transition .

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
2. Study the influence of magnetic configuration (ripple / iota) on biasing induced transitions

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

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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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References

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