TJ-II:Influence of radial electric field on intermittence near rational surfaces

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Experimental campaign

2019 Autumn

Proposal title

Influence of radial electric field on intermittence near rational surfaces

Name and affiliation of proponent

B.P. van Milligen, B.A. Carreras, U. Losada C. Hidalgo

Details of contact person at LNF

N/A

Description of the activity

In previous work, we have established that the intermittence parameter C(1) varies in a systematic way near rational surfaces [B.A. Carreras et al, Intermittency and turbulence in fusion devices, In press (2019)]. This was found to be the case both in a numerical model of resistive MHD turbulence, and confirmed using data from the W7-X stellarator. Hence, the intermittence parameter provides an indirect diagnostic of the magnetic configuration.

In more recent work, the iota scan experiments of 2013[1] were revisited, and a remarkably detailed confirmation of this phenomenon was obtained[2]. The latter paper also suggested that a radial electric field (i.e., poloidal rotation) may affect the intermittence parameter significantly. In the present experiment, we therefore plan to repeat the iota scan experiments while applying a radial electric field, induced via probe biasing.

The plan is to scan iota between configurations 100_40 and 100_44, while the B and D Langmuir probes are located at ρ ≃ 0.85 (the reason being that this scan will move the important 8/5 rational surface across the Langmuir probe location, based on the results from the latest paper cited). The applied voltage to the biasing probe will be [-200, -100, 0, 100, 200], making 5 discharges at each voltage to verify reproducibility.

International or National funding project or entity

Ministerio de Ciencia, Innovación y Universidades Nº PGC2018-097279-B-I00

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 30 discharges, 1 day
  • Essential diagnostic systems: Langmuir probes, biasing probe, Doppler reflectometer
  • Type of plasmas (heating configuration): ECRH, below critical density, constant density if possible

Preferred dates and degree of flexibility

Preferred dates: none

References

  1. B.Ph. van Milligen et al., Parallel and perpendicular turbulence correlation length in the TJ-II stellarator. Nucl. Fusion, 53:093025 (2013)
  2. B.Ph. van Milligen, The localization of low order rationals based on the intermittence parameter in the TJ-II stellarator, Submitted (2019)

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