Comparison of cryogenic (hydrogen) and TESPEL (polystyrene) pellet particle deposition in a magnetically confined plasma

McCarthy, K. J.; Tamura, N.; Combs, S. K.; Panadero, N.; Ascabíbar, E.; Estrada, T.; García, R.; Sánchez, J.; Fraguas, Ángela; Navarro, Moses; Pastor, I.; Soleto, A.; Team, Tj‐Ii

doi:10.1209/0295-5075/120/25001

Cited by 13 publications

(18 citation statements)

References 29 publications

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“…For instance, the large outward drift acceleration experienced by ablated pellet material results in low fuelling efficiencies (<25%) for injections from the outer plasma edge of this device. Indeed, tracer injections with polystyrene (-C 8 H 8 -) based TESPELs have confirmed an inverse mass dependence of the acceleration [16]. Additional experiments have also revealed that enhanced pellet ablation in the plasma core due to fast-electron impacts can lead to higher fuelling efficiencies as the outward drift acceleration is disrupted in the initial drift phase [17].…”

Section: Plasma Fuelling and Impuritiesmentioning

confidence: 93%

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

Hidalgo¹,

Ascasíbar²,

Alegre³

et al. 2022

Nucl. Fusion

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TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.

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Section: Plasma Fuelling and Impuritiesmentioning

confidence: 93%

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

Hidalgo¹,

Ascasíbar²,

Alegre³

et al. 2022

Nucl. Fusion

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“…Additional information on ablation and drift processes is obtained using a fast-frame CMOS camera equipped with a coherent double fibre bundle and interference filters. To date, TESPEL has been used in TJ-II to catalogue spectral line emissions (17 to 200 nm) of non-intrinsic impurities (Al, S, Ca, Sn, and W) [12], to investigate plasma termination and recovery [44], and to compare ablation and cloud drifting for different pellet types [45].…”

Section: Jinst 16 C12026mentioning

confidence: 99%

Plasma diagnostic systems and methods used on the stellarator TJ-II

McCarthy¹

2021

J. Inst.

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The TJ-II is a heliac-type stellarator device with major radius of 1.5 m and averaged minor radius ⩽0.22 m that has been operated at CIEMAT, Madrid since 1998. Its full magnetic field is created by a system of poloidal, central, toroidal and vertical field coils, thus it possesses a fully 3-dimensional plasma structure and a bean-shaped plasma cross-section. Although this results in a complicated vacuum-vessel layout, it has excellent port access for diagnostics (96 portholes). During its initial operational phase, it was equipped with a limited set of essential diagnostics. Since then, a broad variety and large number of both passive and active diagnostics have been installed. The former include Hα monitors, light spectrometers, an electron cyclotron emission radiometer, X-ray filter monitors, neutral particle analysers, magnetic diagnostics, as well as cameras, among others, while the latter include various laser, atomic and ion beam based diagnostics, microwave probe beams, Langmuir probes plus impurity injection techniques. In this paper, after describing the TJ-II stellarator, its heating and fuelling systems, the diagnostic systems employed are outlined and discussed briefly here. Finally, results obtained with selected systems are highlighted.

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“…However, few systematic comparisons of these pellet types exist due to the limited number of devices equipped with both cryogenic and impurity PI systems. Moreover, for reference or comparison purposes, TESPEL pellets with no tracer are sometimes injected in TJ-II [61].…”

Section: Plasma Core Fuelling Pellet Physics and Modellingmentioning

confidence: 99%

Overview of recent TJ-II stellarator results

et al. 2019

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The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presented.

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Comparison of cryogenic (hydrogen) and TESPEL (polystyrene) pellet particle deposition in a magnetically confined plasma

Cited by 13 publications

References 29 publications

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

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

Plasma diagnostic systems and methods used on the stellarator TJ-II

Overview of recent TJ-II stellarator results

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