The Lithium Wall Stellarator Experiment in TJ-II

Tabarés, F.L.; Tafalla, D.; Ferreira, J. A.; Ochando, M. A.; Medina, F.; Ascasíbar, E.; Estrada, T.; Fuentes, C.; Garcı́a-Cortés, I.; Guasp, J.; Liniers, M.; Pastor, I.; Pedrosa, M. A.

doi:10.1585/pfr.5.s1012

Cited by 9 publications

(7 citation statements)

References 17 publications

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“…At high densities, the temperature tends to drop due to radiation effects [43]. In spite of the fact that the discharges are similar but not identical, the mean evolution is rather clear:…”

Section: B Evolution Of Magnetic Activity During L-h Transitionsmentioning

confidence: 95%

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Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Estrada

Carreras²,

Ascasíbar

et al. 2016

Physics of Plasmas

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This work focuses on the relationship between L-H (or L-I) transitions and MHD activity in the low magnetic shear TJ-II stellarator. It is shown that the presence of a low order rational surface in the plasma edge (gradient) region lowers the threshold density for H-mode access. MHD activity is systematically suppressed near the confinement transition.We apply a causality detection technique (based on the Transfer Entropy) to study the relation between magnetic oscillations and locally measured plasma rotation velocity (related to Zonal Flows). For this purpose, we study a large number of discharges in two magnetic configurations, corresponding to 'fast' and 'slow' transitions. With the 'slow' transitions, the developing Zonal Flow prior to the transition is associated with the gradual reduction of magnetic oscillations. The transition itself is marked by a strong spike of 'information transfer' from magnetic to velocity oscillations, suggesting that the magnetic drive may play a role in setting up the final sheared flow responsible for the H-mode transport barrier. Similar observations were made for the 'fast' transitions. Thus, it is shown that magnetic oscillations associated with rational surfaces play an important and active role in confinement transitions, so that electromagnetic effects should be included in any complete transition model.

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“…At high densities, the temperature tends to drop due to radiation effects [43]. In spite of the fact that the discharges are similar but not identical, the mean evolution is rather clear:…”

Section: B Evolution Of Magnetic Activity During L-h Transitionsmentioning

confidence: 95%

“…At high densities, the temperature tends to drop due to radiation effects [43]. In spite of the fact that the discharges are similar but not identical, the mean evolution is rather clear: across the transition, the T e profile is mostly constant or slightly decreasing in amplitude;…”

Section: B Evolution Of Magnetic Activity During L-h Transitionsmentioning

confidence: 95%

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Estrada

Carreras²,

Ascasíbar

et al. 2016

Physics of Plasmas

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“…In the most recent experimental campaign, the TJ-II stellarator was coated with lithium [9]. The technique used for lithiumization is evaporation using ovens and the Li is homogenized in the vessel walls by the plasma which is seen to distribute the Li.…”

Section: Plasma Operation With Li-coated Wallsmentioning

confidence: 99%

Confinement transitions in TJ-II under Li-coated wall conditions

Sánchez¹,

Acedo²,

Alonso³

et al. 2009

Nucl. Fusion

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This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma–wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 1019 m−3 and T e ≈ 250–300 eV, with peaked density, rather flat T e profiles and higher ion temperatures. Due to the achieved density control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Hα emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.

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“…Например, критическим моментом является необходимость обеспечения хороше-го смачивания материалов КПС и ВК, без чего их использование с КПС теряет реальный смысл. Кроме того, хорошая совместимость Li с плазмой токамака, подтверждённая наблюдением улучше-ния параметров плазмы в экспериментах на многочисленных плазменных установках [21][22][23][24][25][26], увеличи-вает привлекательность КПС с Li в качестве обращённого к плазме материала.…”

Section: заключениеunclassified

Comparative Analyses of Low Melting Metals Application With Capillary-Pore Systems in Tokamak Conditions

Lyublinski¹,

Vertkov²,

Семенов³

2015

PAST-TF

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Использование капиллярно-пористых систем (КПС) с жидкими Li, Ga, Sn рассматривается в качестве альтернативы для решения проблемы создания внутрикамерных компонентов (ВК) термоядерного источника нейтронов (ТИН) и реактора типа ДЕМО. Основными преимуществами КПС с жидким металлом по сравнению с твёрдыми материалами являются их устойчивость к деградации свойств в условиях токамака и способность к самовосстановлению поверхности. Оценка при-менимости жидких металлов проводится на основе анализа их физических и химических свойств, взаимодействия с пла з-мой токамака, конструктивных и технологических особенностей ВК с КПС, реализующих применение этих м еталлов в токамаке. Показано, что верхний предел рабочей температуры ВК для всех рассматриваемых легкоплавких металлов л е-жит в интервале 550-600 о С. Для ВК с Li решающим фактором является ограничение по допустимому потоку атомов в плазму, с Ga и Sn -коррозионная стойкость конструкционных материалов. Для рассмотренной перспективной констру к-ции ВК с использованием Li, Ga, Sn верхний предел тепловых нагрузок в стационарном режиме работы близок к 18 -20 МВт/м 2 . Из проведённого анализа видно, что использование металлов с низким давлением равновесного пара (Ga, Sn) не даёт выигрыша в расширении области допустимых рабочих температур ВК. Однако по совокупности свойств, возмо ж-ности реализации эффекта самовосстановления и стабилизации жидкой поверхности, влиянию на па раметры плазменного разряда и способности защитить поверхность ВК в условиях плазменных возмущений и срывов литий является наиболее привлекательным жидким металлом для создания ВК на основе КПС для токамаков.Ключевые слова: капиллярно-пористые системы, легкоплавкие металлы, внутрикамерные элементы, термоядерный реактор, токамак. Capillary-pore systems (CPS) with liquid metals are considered as advanced plasma facing elements (PFE) for application in DEMOtype fusion reactor and fusion neutron source. The main advantages of low melting metals in CPS with respect to solid materials are the possibility to provide surface self-healing and high resistance to degradation of properties. The estimation of opportunity of liquid Li, Ga and Sn application is carried out on the basis of their physical, chemical and technological properties, and with respect to prospective design of the tokamak in-vessel elements. The temperature limit for normal operation of CPS with Li, Ga, Sn is about 550-600 ºC. For Li application it is determined by appropriate flux to the plasma due to evaporation and for Ga and Sn -by corrosion resistance limit. Surface temperature analysis for possible in-vessel element design has shown the similar power flux limit ~18-20 MW/m 2 for Li, Ga and Sn application at normal operation. It is clear that application of liquid metals with low vapor pressure (Ga, Sn) does not increase PFE operation limit. The property combination, well-demonstrated possibility for surface self-healing, favorable effect on tokamak plasma parameters offer the advantage of Li. The CPS with Li has the priority for ELEs and at di...

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The Lithium Wall Stellarator Experiment in TJ-II

Cited by 9 publications

References 17 publications

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Confinement transitions in TJ-II under Li-coated wall conditions

Comparative Analyses of Low Melting Metals Application With Capillary-Pore Systems in Tokamak Conditions

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