TJ-II:Turbulence properties near a rational surface

Experimental campaign

Spring 2022

Proposal title

Turbulence properties near a rational surface

Name and affiliation of proponent

B.P. van Milligen, I. Voldiner, B.A. Carreras, 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. 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 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 [-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: $V_{f},I_{\rm {sat}},E_{r},E_{\theta },v_{\theta },\Gamma$, the RMS of various quantities, long-range correlations between probes B and D, cross phase (between $E_{\theta },I_{\rm {sat}}$), etc.

International or National funding project or entity

N/A

Description of required resources

Required resources:

• Dynamic iota scan between configurations 100_40 and 100_44
• Biasing at fixed voltage [-300, -150, 0, 150, 300]
• 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 ($n_{e}\simeq 0.6\cdot 10^{19}{\mathrm {m} }^{-3}$)

Preferred dates and degree of flexibility

Preferred dates: N/A

References

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