TJ-II: Influence of magnetic configuration on filament dynamics
Experimental campaign
2021
Proposal title
TJ-II: Influence of magnetic configuration on filament dynamics
Name and affiliation of proponent
Daniel Carralero, Ulises Losada, Gustavo Grenfell, Boudewijn van Milligen et al.,
Details of contact person at LNF
Daniel Carralero
Description of the activity
SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) [1]. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes [2], which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them.
In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them [3][4]. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport [5]. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction.
In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments.
While some
TJ-II is [probes B and D] [[6]]. While . This makes TJ-II a unique device to explore (simultaneously) the influence of magnetic curvature on blob dynamics.
The goal of this research proposal is:
1. Characterize filaments and evaluate filament propagation models, already tested in tokamaks.
2. Describe and understand the effect of topologic features (e.g. islands, different curvature and connection lengths, etc.) to filament characteristics.
International or National funding project or entity
If applicable, enter funding here or write N/A
Description of required resources
Required resources:
- Number of plasma discharges or days of operation:
- Essential diagnostic systems: Dual Langmuir probe system in TJ-II
- 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
Preferred dates: (format dd-mm-yyyy)
References
- ↑ S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717
- ↑ P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307
- ↑ D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4
- ↑ D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002
- ↑ C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003
- ↑ T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)