Suprathermal ion studies in ECRH and NBI phases of the TJ-II stellarator

Zurro, B.; Baciero, A.; Tribaldos, V.; Liniers, M.; Cappa, Á.; Löpez‐Fraguas, A.; Jiménez-Rey, D.; Fontdecaba, J. M.; Nekhaieva, O.M.

doi:10.1088/0029-5515/53/8/083017

Cited by 28 publications

(28 citation statements)

References 31 publications

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“…The result of this analytical consideration was fully confirmed by numerical simulations (Embréus et al 2015). Such "runaway" ions are routinely detected in laboratory experimens (Helander et al 2002;Fülöp & Landreman 2013;Zurro et al 2013;Eilerman et al 2015).…”

Section: Ion Trapssupporting

confidence: 55%

Ion Traps at the Sun: Implications for Elemental Fractionation

Fleishman

Musset

Bommier

et al. 2018

ApJ

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Why the tenuous solar outer atmosphere, or corona, is much hotter than the underlying layers remains one of the greatest challenge for solar modeling. Detailed diagnostics of the coronal thermal structure come from extreme ultraviolet (EUV) emission. The EUV emission is produced by heavy ions in various ionization states and depends on the amount of these ions and on plasma temperature and density. Any nonuniformity of the elemental distribution in space or variability in time affects thermal diagnostics of the corona. Here we theoretically predict ionized chemical element concentrations in some areas of the solar atmosphere, where the electric current is directed upward. We then detect these areas observationally, by comparing the electric current density with the EUV brightness in an active region. We found a significant excess in EUV brightness in the areas with positive current density rather than negative. Therefore, we report the observational discovery of substantial concentrations of heavy ions in current-carrying magnetic flux tubes, which might have important implications for the elemental fractionation in the solar corona known as the first ionization potential (FIP) effect. We call such areas of heavy ion concentration the "ion traps." These traps hold enhanced ion levels until they are disrupted by a flare whether large or small.

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Section: Ion Trapssupporting

confidence: 55%

Ion Traps at the Sun: Implications for Elemental Fractionation

Fleishman

Musset

Bommier

et al. 2018

ApJ

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“…The high sensitivity of the LP, and its operation in a height pulse analysis regime, with an ad hoc digital pulse algorithm, allows the exploration of physical problems related to escaping ions that are not accessible to other scintillator probe set‐ups. Correct operation of the LP in the former mode was demonstrated previously in ECRH and NBI plasmas of TJ‐II by comparison with spectroscopy methods . Finally, this LP was previously operated with a SrGa2S4:Eu phosphor screen (TG‐Green, decay time = 540 ns) .…”

Section: Introductionmentioning

confidence: 70%

“…In addition, very often, the standard methods for measuring ion temperature ( T i ) are not optimized to simultaneously monitor the fast‐ion component. Hence, an LP may help to quantify this component and evaluate its importance for the total ion power balance, this having been shown to be non‐negligible in the case of TJ‐II . In TJ‐II, an LP, also know as a fast‐ion loss detector (FILD), is located outside the last closed flux surface (LCFS) of the plasma.…”

Section: Introductionmentioning

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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“…The parametric decay instabilities (PDIs), which can accompany the ECRH experiments, are believed to be deeply suppressed by the huge energy loss of daughter waves from the decay region, according to the predictions of theory developed in 80 th [1]. However, during the last decade numerous ECRH experiments performed at TEXTOR, TCV, TJ-II, ASDEX-UG, LHD, T-10 and FTU [2][3][4][5][6][7][8][9][10][11][12][13] have demonstrated excitation of the anomalous phenomena. The clearest evidence of the nonlinear phenomena excitation was obtained at TEXTOR [2,3] where the strong backscattering signals down-shifted in frequency and amplitude modulated at the frequency of magnetic island were observed.…”

Section: Introductionmentioning

confidence: 99%

Anomalous absorption in ECRH experiments due to the parametric low-threshold excitation of localized UH waves

Popov

Gusakov

2019

EPJ Web Conf.

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We describe the theoretical model which interprets the anomalous phenomena, i.e. the generation of backscattering signal observed in the ECRH experiments at TEXTOR, TCV, TJ-II, ASDEX-UG, LHD and FTU, as a consequence of the excitation of the parametric decay instability (PDI) leading to anomalous damping of the pump wave. The PDI power-threshold is shown to be extremely low due to the localization of both or one daughter upper hybrid (UH) waves in presence of a nonmonotonic (hollow) density profile, which is often observed in the ECRH experiments due to the magnetic island or the density pump-out effect. In the case of the extraordinary wave pump the model predicts substantial (up to 25%) anomalous absorption in the electron channel and explains the anomalous ion acceleration by the generation of secondary low frequency waves which directly transfer the pump power to the ion component. The possibility of anomalous absorption of the O-mode pump in the ECRH experiment due to the parametric excitation of trapped UH wave is also discussed and the anomalous absorption rate at the 10% level is predicted.

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Suprathermal ion studies in ECRH and NBI phases of the TJ-II stellarator

Cited by 28 publications

References 31 publications

Ion Traps at the Sun: Implications for Elemental Fractionation

Ion Traps at the Sun: Implications for Elemental Fractionation

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

Anomalous absorption in ECRH experiments due to the parametric low-threshold excitation of localized UH waves

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