TJ-II:Turbulence properties near a rational surface
Turbulence properties near a rational surface
Name and affiliation of proponent
Details of contact person at LNF
Description of the activity
In previous work, we have established that the intermittence parameter C(1) varies in a systematic way near rational surfaces. 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 were revisited, and a remarkably detailed confirmation of this phenomenon was obtained. 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 (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 [-300, -150, 0, 150, 300], making 5 discharges at each voltage to verify reproducibility. Apart from intermittence, we will quantify all other turbulence parameters that can be measured by the probes: , the RMS of various quantities, long-range correlations between probes B and D, cross phase (between ), etc.
International or National funding project or entity
Description of required resources
- Dynamic iota scan between configurations 100_40 and 100_44
- OH current control
- Biasing at fixed voltage [-300, -150, 0, 150, 300] V
- Number of plasma discharges or days of operation: 30 discharges, 1 day
- Essential diagnostic systems: Langmuir probes
- Desirable diagnostic systems: Doppler reflectometer, HIBP (at similar radial positions as the Langmuir probes)
- Type of plasmas (heating configuration): ECRH heated, density constant, below critical density ()
Preferred dates and degree of flexibility
Preferred dates: N/A
- B. Carreras, L. García, J. Nicolau, B. van Milligen, U. Hoefel, M. Hirsch, and the TJ-II and W7-X Teams. Intermittence and turbulence in fusion devices. Plasma Phys. Control. Fusion, 62:025011, 2020.
- B.Ph. van Milligen et al., Parallel and perpendicular turbulence correlation length in the TJ-II stellarator. Nucl. Fusion, 53:093025 (2013)
- B. P. van Milligen, B. Carreras, L. García, and C. Hidalgo. The localization of low order rational surfaces based on the intermittence parameter in the TJ-II stellarator. Nucl. Fusion, 60:056010, 2020.
- B.Ph. van Milligen, B.A. Carreras, L. García, G. Grenfell, I. Voldiner, C. Hidalgo, and the TJ-II Team. The impact of radial electric fields and plasma rotation on intermittence in TJ-II. Plasma Phys. Control. Fusion, 2021.
- B. van Milligen, B. Carreras, I. Voldiner, U. Losada, C. Hidalgo, and the TJ-II Team. Causality, intermittence and crossphase evolution during confinement transitions in the TJ-II stellarator. Phys. Plasmas, 28:092302, 2021.