TJ-II:Turbulence and flow measured at the 3/2 magnetic island using Doppler reflectometry
Turbulence and flow measured at the 3/2 magnetic island using Doppler reflectometry
Name and affiliation of proponent
T. Estrada (1), E. Ascasíbar, E. Maragkoudakis, C. Hidalgo, A. de la Peña, F. Lapayese
Details of contact person at LNF
Description of the activity
The impact of magnetic island on turbulence and flows has been studied in different fusion devices finding differences that depend, among other parameters, on the island width. A vortex-like flow has been measured at large magnetic islands in several devices (e.g. LHD  and TJ-II ). Narrower islands however show a different flow pattern without signatures of flow reversal at the island O-point (e.g. LHD  and W7-X ). These observations are qualitatively reproduced by gyrokinetic simulations . Regarding the impact on the turbulence, a turbulence reduction associated to the island has been found localized nearby the island O-point, both in experiments and simulations [3, 4]. The minimum in the turbulence level nearby the island O-point may be consequence of the strong flow-shear developed at the island boundaries that precludes the spreading of the turbulence into the island.
On the other hand, differences in the flow measured across the island O-point and the island X-point have been found in HL-2A , with stronger flow-shear at the island boundaries at the O-point and a nearly flat flow profile at the X-point. This difference has been also studied theoretically  showing that the flow-shearing near the X-point is important for the turbulence penetration into the island. Such a turbulence spreading into the island has been demonstrated experimentally in several devices: DIII-D , HL-2A , and KSTAR .
In this proposal, we would like to extend the characterization of the turbulence and flow associated to a low order magnetic island carried out in TJ-II . In those experiments, the radial position of the 3/2 magnetic island was scanned along the plasma discharge tailoring the rotational transform profile by means of OH current external induction. The characteristic signatures of the magnetic island were detected as it crossed the Doppler reflectometer measurement position. In the present proposal however, we will try to fix the radial position of the magnetic island by using the operational mode called C-mode; this mode allows sweeping the radial position of the magnetic island up to a given position in a controlled way (see experiments in ). This scheme would allow the comparison of the turbulence and flow measured across the island at the two poloidal regions accessible by the Doppler reflectometer.
 K. Ida et al., Phys. Rev. Lett. 88, 015002 (2001)
 T. Estrada et al., Nucl. Fusion 56, 026011 (2016)
 T. Estrada et al., Nucl. Fusion 61, 096011 (2021)
 A. Bañón-Navarro et al., Plasma Phys. Control. Fusion 59, 034004 (2017)
 M. Jiang et al., Nucl. Fusion 58, 026002 (2017)
 T.S. Hahm et al., Phys. Plasmas 28, 022302 (2021)
 K. Ida et al., Phys. Rev. Lett. 120, 245001 (2018)
 M. Jiang et al., Nucl. Fusion 59, 066019 (2019)
 M.J. Choi et al., Nat. Commun. 12, 375 (2021)
 F. Fernández-Marina et al., Phys. Plasmas 24, 072513 (2017)
International or National funding project or entity
Include funding here (grants, national plans)
Description of required resources
- Number of plasma discharges or days of operation: one experimental day is required as several attempts will be needed in order to get the desired evolution of the plasma current. Then, reproducible discharges are needed in order to properly characterize the magnetic island at the two separate poloidal positions accessible by the Doppler reflectometer.
- Essential diagnostic systems: Microwave interferometer, Rogosky coils, Doppler reflectometer, Thomson scattering, diamagnetic loop , bolometers, Hα detectors, Mirnov coils, SXR.
- Type of plasmas (heating configuration): ECH plasmas in the standard magnetic configuration with OH current programmed using C-mode operation.
- Specific requirements on wall conditioning if any: Fresh Li is required for a good density control.
- External users: need a local computer account for data access: no
- Any external equipment to be integrated? Provide description and integration needs:
Preferred dates and degree of flexibility
Preferred dates: (format dd-mm-yyyy)