“…1), and tungsten in the LH grill's four lateral limiters (since 2018, before they were graphite). While first aspects presented are focusing on the characterization of ICRH-related sources of impuritiesalready well-documented by past experiments in other devices [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] an important goal of this study (by collecting information on different regions at the same time), is to provide new information on the rather local or global character of dominant mechanisms, with efforts to also disentangle the so-called near from far RF fields effects. Comparisons between different campaigns and magnetic configurations were exploited to extract qualitative information on impurity sources.…”
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de
“…1), and tungsten in the LH grill's four lateral limiters (since 2018, before they were graphite). While first aspects presented are focusing on the characterization of ICRH-related sources of impuritiesalready well-documented by past experiments in other devices [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] an important goal of this study (by collecting information on different regions at the same time), is to provide new information on the rather local or global character of dominant mechanisms, with efforts to also disentangle the so-called near from far RF fields effects. Comparisons between different campaigns and magnetic configurations were exploited to extract qualitative information on impurity sources.…”
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de
“…Erosion-redeposition modelling of edge beryllium line spectroscopy of localized, ICRF sheath-enhanced emission at magnetically connected JET outer limiters was also shown to be consistent with increased local erosion [11,12]. An excellent overview of ICRF-induced plasma surface interaction is provided by [13], while a discussion about tungsten management for H-mode scenario's optimization in JET can be found under [14]. Among numerous 2D mapping experiments based on SOL parameters scan at antennas surrounding using various diagnostics like Retarding Field Analyzer [15], Langmuir probes [16], Lithium beam [17], Gas puff imaging [18] or Infrared Camera (IR) [3] some global trends are common to many physical values, suggesting RF-sheath somehow modifies several parameters with a reproducible fashion.…”
Section: Introductionmentioning
confidence: 76%
“…4a is centred on the parallel wave vector k||=11rad/m. This is not only because high k|| spectra usually result in better absorption efficiencies, but also because this is the phasing that minimizes the excitation of RF-sheath that can have a deleterious influence on plasma surface interaction [13,43] which is shown in the next section. However, since commissioning several systems simultaneously required setting priorities, efforts focused on matching optimization, to the detriment of accurate phasing control up to summer 2019.…”
Plasma heating in the full Tungsten (W) Environment in Steady-state Tokamak (WEST) relies on electromagnetic waves in both Lower Hybrid (LH) and Ion Cyclotron Range of Frequencies (ICRF). The present study focuses mostly on the optimization of discharges heated with ICRF, by reporting different methods to first optimize wave coupling, optimize their absorption and reduce the impurity production. It is shown that ICRF coupling can be optimized either by moving the plasma closer to antennas, increasing the plasma density, wave frequency and LH power. We show that the absorption efficiency correlates with the hydrogen concentration with the existence of an optimum between 7 and 10% as expected for a minority heating scenario.Absolutely calibrated visible spectroscopy sightlines were used to monitor ion fluxes in different locations as part of an effort to quantitively estimate the contribution of different impurity sources to the core contamination by tungsten. It is typically found that in discharges with high total RF-power (above 5MW of LH and 3MW of ICRF), divertor and antenna limiter sources can reach similar order of magnitude during the ICRF phase.
An ion cyclotron resonance heating (ICRH) antenna system must launch radio frequency (RF) power with a wavenumber spectrum which maximizes the coupling to the plasma. It should also ensure good absorption while minimizing the wave interaction with the plasma edge. Such interactions lead to impurity release, whose effect has been measured far from the antenna location (Klepper et al. 2013; Wukitch et al. 2017; Perkins et al. 2019) and can involve the entire scrape-off layer. In the normal heating scenario, for which the frequency of the waves launched by the antenna is larger than the ion cyclotron frequency of the majority ions
$\omega > \omega _{\textrm {ci},\textrm {maj}}$
, release of impurities due to ICRH can be affected by minimizing the low
$|k_{\parallel }| < k_0$
power spectrum components of the antenna. Impurity release can be the result of low central absorption of the waves or power transfer from the fast to the slow wave due to the presence of a confluence in the plasma edge. In ASDEX Upgrade (AUG), a reduction of heavy impurity release by ICRH in the plasma was qualitatively well correlated to the parallel electric field and RF currents flowing around the antenna (Bobkov et al. 2017). In this article, we first show a correlation between the reduction in impurity release by ICRH in AUG and the rejection of the low
$|k_{\parallel }| < k_0$
region of the antenna power spectrum. We show that the same correlation holds for results obtained in the Alcator C-Mod tokamak. Finally, using this idea, we reproduce ICRH induced impurity release behaviour in a not yet published experiments of JET, and make predictions for ITER and DEMO.
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