Beamline duct monitoring of the TJ-II neutral beam injectors

Liniers, M.; Wolfers, G.; Sebastián, J.A.; Rojo, B.; Martín, Fernando; Carrasco, R. C.; Guasp, J.; Martín, Francisco; Sánchez, E.; Jiménez, Andrés F; Merino, Guillermo; Ochando, M. A.; McCarthy, K. J.; Ascasíbar, E.; Zurro, B.; Alonso, Alfonso Soleto y Javier

doi:10.1016/j.fusengdes.2013.04.014

Cited by 15 publications

(11 citation statements)

References 4 publications

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“…Beams of similar power on the V-calorimeter deposit similar power on the duct scrapers. Reionization losses are also similar in both injectors, as obtained by IR measurements [37]. Nevertheless, shots with similar plasma parameters and similar available power, #54097 for NBI1 and #53605 for NBI2, exhibit quite different absolute values of plasma current, 0.6 kA and 2.0 kA respectively.…”

Section: Discussionsupporting

confidence: 73%

Validating neutral-beam current drive simulations in the TJ-II stellarator

Mulas¹,

Cappa²,

Martínez-Fernández³

et al. 2023

Preprint

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In this paper, we analyze the results of neutral-beam current drive (NBCD) experiments, performed in the TJ-II stellarator, with the aim of validating the theoretical predictions. Both parallel and anti-parallel injection with respect to the magnetic field were explored using co (NBI1) and counter (NBI2) beams at different injected beam power and plasma densities. The fast-ion current driven by both beams was simulated with the Monte Carlo code ASCOT and the electron response to the fast-ion current was calculated analytically using a model valid for an arbitrary magnetic configuration and a low collisionality plasma. The model reproduces with rather good agreement the toroidal current measured in NBI2 plasmas while the current driven by NBI1 is less than half the predicted one. Possible reasons for this discrepancy are discussed.

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Section: Discussionsupporting

confidence: 73%

Validating neutral-beam current drive simulations in the TJ-II stellarator

Mulas¹,

Cappa²,

Martínez-Fernández³

et al. 2023

Preprint

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“…The first point to be considered is that the NBI system can be an additional source of iron through two contributions: beam interaction of the counter-NBI with the duct [52] and shine-through neutrals from both NBIs colliding with the vacuum vessel [53]; the former should constitute a constant source of iron up to t = 1020 ms, while the latter should cause an increasing iron source during the length of the discharge, since lower density leads to increased shine-through. From the fact that the iron content keeps increasing tens of milliseconds after the counter-NBI has been switched-off (the confinement time for iron in low-density ECH-heated plasmas of TJ-II is between 5 and 10 ms [54]), while the density is decreasing, we infer that the shine-through has a measurable contribution to the iron source; the observed change in the VUV signal around t = 1060 ms would then be caused by transport.…”

Section: Tj-iimentioning

confidence: 99%

Moderation of neoclassical impurity accumulation in high temperature plasmas of helical devices

Velasco¹,

Calvo²,

Satake³

et al. 2016

Nucl. Fusion

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Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, and this is particularly the case of helical reactors, whose low-collisionality ion-root operation scenarios usually display a negative radial electric field which is expected to cause inwards impurity pinch. In this work we discuss, based on experimental measurements and standard predictions of neoclassical theory, how plasmas of very low ion collisionality, similar to those observed in the impurity hole of the Large Helical Device [1-3], can be an exception to this general rule, and how a negative radial electric field can coexist with an outward impurity flux. This interpretation is supported by comparison with documented discharges available in the International Stellarator-Heliotron Profile Database, and it can be extrapolated to show that achievement of high ion temperature in the core of helical devices is not fundamentally incompatible with low core impurity content.

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“…Higher‐density plasmas are achieved using NBI heating. TJ‐II has two such injectors, each of which delivers up to 500 kW of through‐port power ( P NBI ) of neutral hydrogen accelerated to 32 keV during ≤120 ms . One of them (the co‐injector, NBI‐1) is directed parallel to the toroidal magnetic field B 0 , while the other is directed in the opposite direction (the counter‐injector, NBI‐2) .…”

Section: Experiments and Lp Set‐upmentioning

confidence: 99%

Discrete fast‐ion detection with energy discrimination in plasmas having edge‐localized mode‐like instabilities in the stellarator TJ‐II

Martínez

Zurro²,

Baciero³

et al. 2018

Contributions to Plasma Physics

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The existence of a population of ions, with energies well above the corresponding thermal values, in plasmas heated by neutral beam injection (NBI) in the stellarator TJ-II and in other magnetically confined plasmas devices is well known. Moreover, during the NBI phase of the TJ-II, edge-localized mode-like (ELM-like) instabilities often appear. This work studies the relationship between fast ions escaping from TJ-II plasmas and such ELM-like events. For this, an ion luminescent probe (LP), operated with a fast scintillator (decay time = 27 ns) and high-speed conditioning electronics (100 MHz), is used to measure, without pile-up effects, the energy distribution of suprathermal ions across the energy range, from 1 to 30 keV. It is found that the LP detects suprathermal ion populations that can be related to ELM-like events whose temperatures oscillate between 0.5 and 3 keV and that can be distinguished in a spectrogram of the LP response as an increase in frequencies from 15 to 150 kHz. Finally, observations of substructures within ELM-likes events, consisting of bursts of ions, with times between 5 and 15 μs are also reported. Such substructures have been observed previously in both tokamaks and stellarators in ion saturation current, high-speed camera images, etc. However, understanding the fast-ion component can provide new and relevant information about the behaviour of ions.

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Beamline duct monitoring of the TJ-II neutral beam injectors

Cited by 15 publications

References 4 publications

Validating neutral-beam current drive simulations in the TJ-II stellarator

Validating neutral-beam current drive simulations in the TJ-II stellarator

Moderation of neoclassical impurity accumulation in high temperature plasmas of helical devices

Discrete fast‐ion detection with energy discrimination in plasmas having edge‐localized mode‐like instabilities in the stellarator TJ‐II

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