Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Hidalgo, C.; Ascasíbar, E.; Alegre, D.; Alonso, A.; Antón, R.; Baciero, A.; Baldzuhn, J.; Barcala, J.M.; Barrera, L.; Blanco, E.; Botija, J.; Bueno, L.; Cabrera, Santiago; Cal, E. de la; Calvo, I.; Cappa, Á.; Carralero, D.; Carrasco, R. C.; Carreras, B. A.; Castro, R.; Castro, Alfonso; Cebrián, L.; Chmyga, A. A.; Chamorro, M.; Colino, P.; Aragón, F.; Drabinskiy, M.A.; Duque, J.; Eliseev, L.G.; Escoto, F.J.; Estrada, T.; Ezzat, Mohamed; Fraguas, F.; Fernández-Ruiz, D.; Fontdecaba, J. M.; Gabriel, A. H.; Gadariya, D.; Garcia, L.; Garcı́a-Cortés, I.; García-Gómez, R.; García-Regaña, J. M.; González-Jerez, A.; Grenfell, G.; Guasp, J.; Guisse, V.; Hernández-Sánchez, J.; Hernanz, J.; Jiménez-Denche, A.; Khabanov, P.O.; Kharchev, N. K.; Kleiber, R.; Koechl, F.; Kobayashi, Tatsuya; Kocsis, G.; Koepke, M. E.; Kozachek, A.S.; Krupnik, L. I.; Lapayese, F.; Liniers, M.; Liu, B.; López‐Bruna, D.; López-Miranda, B.; Losada, U.; Luna, E. de la; Лысенко, С. Е.; Martín-Díaz, F.; Martín-Gómez, G.; Maragkoudakis, E.; Martínez-Fernández, J.; McCarthy, K. J.; Medina, F.; Medrano, M.; Melnikov, A. V.; Méndez, P.; Miguel, Francisco Javier Tamayo de; Milligen, B. Ph. van; Molinero, A.; Motojima, G.; Mulas, S.; Narushima, Y.; Navarro, Moses; Nedzelskiy, I. S.; Nuñez, R.; Ochando, M. A.; Ohshima, S.; Oyarzábal, E.; Pablos, J.L. de; Palomares, F.; Panadero, N.; Papoušek, F.; Parra, Félix I.; Sempere, Carmen Pastor; Pastor, I.; Peña, A. de la; Peralta, R.; Pereira, A.; Pons-Villalonga, P.; Polaino, H.; Portas, A.; Poveda, E.; Ramos, Francisco José; Rattá, G.A.; Redondo, M.; Reynoso, C.; Rincón, E.; Rodríguez-Fernández, C.; Rodrı́guez-Rodrigo, L.; Ros, Agustin J.; Sánchez, E.; Sanchez, J.; Sánchez-Sarabia, E.; Satake, S.; Sebastián, J.A.; Sharma, R.; Smith, N.; Silva, Carlos; Solano, E.R.; Soleto, A.; Spolaore, M.; Szepesi, T.; Tabarés, F.L.; Tafalla, D.; Takahashi, H.; Tamura, N.; Thienpondt, H.; Tolkachev, A.; Unamuno, R.; Varela, J.; Vega, J.; Velasco, J. L.; Voldiner, I.; Yamamoto, Satoshi; Team, the TJ-II

doi:10.1088/1741-4326/ac2ca1

Cited by 13 publications

(12 citation statements)

References 56 publications

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“…The experimental results reported here provide very detailed information regarding the structure of the poloidal velocity (equivalent to E r ) at the TJ-II stellarator [10]. This structure is clarified by scanning the rotational transform profile dynamically during a discharge, while a Langmuir probe performed measurements at a fixed location well inside the plasma.…”

Section: Introductionmentioning

confidence: 88%

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Rational surfaces, flows and radial structure in the TJ-II stellarator

et al. 2022

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In this work, we perform a rotational transform scan in the TJ-II stellarator, while measuring several turbulent quantities well inside the plasma edge by means of a Langmuir probe and applying a radial electric field to the edge plasma using a biasing probe. By calculating the intermittence parameter from floating potential measurements, we are able to identify a major low order rational surface and hence relate the probe measurements to the local value of the rotational transform. Based on the former, we are able to show that the poloidal plasma velocity (and hence radial electric field) has a significant radial structure that is clearly related to the rotational transform profile and in particular the lowest order rational surfaces in the range studied. The poloidal velocity is also affected by the edge biasing. The particle flux Γ was also found to exhibit a radial pattern, as did the flow shear suppression term ωE×B, but their relation to the low-order rational surfaces was less clear. We surmise that this lack of direct correspondence is due to an unknown term in the turbulence evolution equation: the instability growth rate, γ. We make use of a reduced Magnetohydrodynamic turbulence model to interpret the results. Overall, a picture is obtained in which the plasma self-organizes towards a state with a clear radial pattern of the radial electric field, in line with expectations from some numerical studies describing the spontaneous formation of an ‘E × B staircase’, consistence of alternating layers with fast and slow radial transport. In this state, profiles of various quantities (density, temperature, pressure) will not be smooth.

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Section: Introductionmentioning

confidence: 88%

“…The TJ-II stellarator is a flexible Heliac [12] with toroidal magnetic field B T ≃ 1 T, major radius R 0 = 1.5 m and minor radius a < 0.22 m [10]. In the experiments discussed here, plasmas were heated using two ECRH beam lines delivering up to 300 kW each at a frequency of 53.2 GHz (X mode).…”

Section: Methodsmentioning

confidence: 99%

Rational surfaces, flows and radial structure in the TJ-II stellarator

et al. 2022

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“…The particle loss associated with the energetic particle-driven AE can deteriorate the confinement but may also have an indirect, positive effect on confinement by inducing local changes in Er with an impact on the turbulence regulation by E×B flows. The relation between zonal structures and AE has been experimentally studied using HIBP [80]. LRCs are detected both at the AE and at the ZF frequencies, but so far no causal relationship could be established between the amplitude of ZFs and AEs.…”

Section: H-mode Transitionmentioning

confidence: 99%

H-mode transition in the TJ-II stellarator plasmas

Estrada¹,

Hidalgo²

2023

Phil. Trans. R. Soc. A.

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Since the first H-mode transitions were observed in TJ-II plasmas in 2008, an extensive experimental effort has been done aiming at better physics understanding of confinement transitions. In this article, an overview of the main findings related to the L-H transition in TJ-II is presented including how the radial electric field is driven, what are the possible mechanisms for turbulence suppression and what are the related temporal and spatial scales that can impact the transition. The trigger of the L-H transition in TJ-II plasmas is found to be more correlated with the development of fluctuating E × B flows than with steady-state E r effects, pointing to the role played by zonal flows in mediating the transition. Experimental evidence supporting the predator–prey relationship between turbulence and flows as the basis for the L-H transition, found for the first time in TJ-II, reinforces this conclusion. Besides, the reduction in the turbulent transport at the transition is detected at the barrier region but also in a wider radial range with weak or even zero E × B flow shear, which points to other mechanisms beyond the turbulence suppression by local sheared flows. This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.

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“…The FAR3d code has been verified through participation in benchmarking studies of gyro-kinetic and hybrid codes [72] and show a reasonable agreement with the experimental data. FAR3d has been validated against linear AE stability in LHD [73][74][75][76], TJ-II [50,77,78] and DIII-D [56,58]. The nonlinear version of the code has analyzed successfully the sawtoothlike, internal collapse events, EIC and TAE burst observed in LHD plasma [79][80][81][82][83][84] and the AE saturation in DIII-D plasma [85].…”

Section: Numerical Modelmentioning

confidence: 99%

Study of Alfvén eigenmode stability in Quasi-Poloidal Stellarator (QPS) plasma using a Landau closure model

Luengo

Varela²,

Spong³

et al. 2023

Nucl. Fusion

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The aim of this study is to analyze the linear stability of Alfvén Eigenmodes (AE) in QPS device heated by a tangential NBI. The analysis is performed using the gyro-fluid code FAR3d, that solves the reduced MHD equations for the thermal plasma coupled with moments of the kinetic equation for the energetic particles (EP). The AE stability is calculated in several operational regimes of the tangential NBI: EP β between 0.001 − 0.1, EP energy between 12−180 keV and different radial locations of the beam. The analysis is performed for vacuum and finite β equilibria as well as QPS configurations with 2 and 3 periods. The EP β threshold in the vacuum case is 0.001 and the AE frequency is lower as the energy of the EP population decreases. Toroidal Alfvén Eigenmodes (TAEs) with f = 80 − 120 kHz and Elliptical AE (EAEs) between f = 120 − 350 kHz are triggered between the middle-outer plasma region (r/a > 0.5). The AE stability improves in the simulations with finite β equilibria and 3 period configurations with respect to the vacuum case with 2 periods because the continuum gaps are slender, leading to a higher threshold of the EP β, above 0.03 for the AEs triggered by the helical mode families. Helical effects are not strong enough to destabilize Helical Alfvén Eigenmodes (HAEs), the AEs with the largest growth rates are triggered by the n = 1 and n = 2 toroidal families.

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Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Cited by 13 publications

References 56 publications

Rational surfaces, flows and radial structure in the TJ-II stellarator

Rational surfaces, flows and radial structure in the TJ-II stellarator

H-mode transition in the TJ-II stellarator plasmas

Study of Alfvén eigenmode stability in Quasi-Poloidal Stellarator (QPS) plasma using a Landau closure model

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