Neutral Flux Research Articles

Abstract IBEX observes a globally distributed energetic neutral atom (ENA) flux from the heliosheath and very local interstellar medium (VLISM). Over a 14 yr period, Voyager 1 and Voyager 2 traversed the heliosheath from the termination shock to the heliopause. In situ observations from these spacecraft place important constraints on the parent ion populations of the ENAs from the heliosheath in two directions on the upwind side of the heliosphere, i.e., the direction of motion of the Sun in the local interstellar medium. In this study, an MHD model that is constrained by Voyager in situ observations is used to estimate the contribution from the heliosheath to the total ENA fluxes observed by IBEX. At energies greater than about 0.5 keV, the heliosheath provides a significant fraction of the observed ENA flux. However, at energies less than about 0.5 keV, the heliosheath provides an insignificant fraction of the observed ENA flux. These results are the same for both directions, and since the Voyager 1 and 2 directions are not particularly unique, the results are likely to be applicable for much of the upwind hemisphere. Fundamentally, it is the physics of the termination shock and the thickness of the heliosheath that determine the energy-dependent contributions to the observed ENA flux from this region. Because the heliosheath source is insignificant, most ENAs at energies less than about 0.5 keV probably come from the VLISM.

Interstellar Boundary Explorer images have revealed a globally distributed flux of energetic neutral atoms (ENAs) at ∼0.2-6 keV while Cassini observed an ENA belt at 5-55 keV likely originating from the inner heliosheath (IHS) protons via charge exchange with penetrating interstellar neutrals. Such ENAs are considered to reflect solar wind variations to some extent. We explore ENA flux sensitivity in the IHS to solar wind changes at Carrington rotation (CR) resolution and quantify its dependence on IHS ion distributions. We utilized three models for ion distributions designed to respond to solar wind changes upstream of the termination shock (TS), from which the corresponding variations in ENA fluxes were computed. All three ion models employ a regularized kappa distribution for solar wind protons. The models differ in the treatment of transmitted pickup ions (PUIs) and reflected PUIs with different combinations of regularized kappa and filled-shell distributions. Our ENA estimates reveal the potential for substantial flux change rates between adjacent CR times, often exceeding several tens of percent, a feature not recognized in previous studies. Such rapid variations in ENA flux levels exhibit a correlation with concurrent fluctuations in solar wind speed and density upstream of the TS. However, the specific characteristics of these ENA changes are contingent on the ion distribution model and the energy considered. Most notably, employing the filled-shell distribution for transmitted PUIs induces noticeable alterations in ENA flux near their cutoff energy ( 0.5-1.5 keV), responding promptly to rapid variations in solar wind bulk speed. Furthermore, the inclusion of reflected PUIs is critical in the high-energy regime (>∼10 keV), which is typically associated with coronal hole fast streams, where ENA fluxes exhibit strong correlations with changes in the solar wind bulk speed and dynamic pressure. The results underscore the importance of precise PUI information in the IHS for accurate ENA estimation during swift solar wind changes.

Abstract The present work is focused on a 3D numerical assessment of the Wendelstein 7-X (W7-X) particle exhaust. For all the numerical simulations the direct simulation Monte Carlo solver of the DIVGAS workflow, has been employed. The complex 3D geometry of the sub-divertor region includes the pumping gap panel, supporting structures, cooling pipes as well as the cryo-vacuum pump. All the considered flow simulations correspond to the Standard magnetic configuration of W7-X. The main conclusions, which can be extracted from the present numerical analysis could be summarized as follows; The coupling between EMC3-EIRENE and DIVGAS, which considers the fact that the incoming neutral particle flux at the sub-divertor is based on realistic plasma background, has been demonstrated. Three plasma scenarios have been considered, for which is clearly seen that by increasing the heating power, the neutral pressure as well as the resulting pumping efficiency is increased. The obtained numerical results of the neutral pressure in the sub-divertor lie within a more general scan matrix, which assumes a wider range of incoming particle flux, namely 1019–1024 (s−1). It has been observed that, the sub-divertor neutral pressure is proportional to the incoming neutral particle flux, with the effective pumping speed to be a constant of proportionality. The influence of switching off the cryo-vacuum pump on the sub-divertor pressure is rather modest and a weak increase of the neutral pressure in the sub-divertor is expected. Correlations of the sub-divertor pressure with the total incoming particle flux as well as the individual pumped flux at each of the AEH and AEP sections have been deduced. Moreover, it has been demonstrated that the influence of the incoming neutral particle flux on the albedo coefficient at the AEH and AEP pumping gaps is rather weak. All the above numerical findings will actively support the optimization of the W7-X particle exhaust, in view of future experimental campaigns.

The recent work of Brown et al. (arXiv:2411.03447) demonstrated that the low-temperature evaporation rate of a large near-extremal charged black hole is significantly reduced from semiclassical expectations. The quantum corrections responsible for the deviation come from Schwarzian modes of an emergent Jackiw-Teitelboim gravity description of the near-horizon geometry of the black hole. Using a one-parameter family of non-perturbative Airy completions, we extend these results to incorporate non-perturbative effects. At large parameter value, the non-perturbative evaporation rate is even smaller than the perturbative JT gravity results. The disparity becomes especially pronounced at very low energies, where the non-perturbative neutral Hawking flux is suppressed by a double exponential in the entropy of the black hole, effectively stopping its evaporation until the next charged particle is emitted via the Schwinger effect. We also explore an alternative family of Bessel completions for which the non-perturbative energy flux exceeds the perturbative JT gravity prediction.

An E parallel B type neutral particle analyzer (E//B NPA) with mass and energy resolution has been developed and successfully conducted its first experiment on the HL-3 tokamak. The mass and energy calibration of the E//B NPA was performed using H + and D + beams on a 300 kV ion accelerator. Results indicate that the E//B NPA is capable of detecting H + in the energy range of 27.4 keV to 462.4 keV and D + in the range of 15.6 keV to 233.4 keV, with an energy resolution of less than 10%. Thanks to background resolving ability of LYSO+SiPM detector module, a novel method was employed for data analysis during the first experiment conducted on the HL-3 tokamak. Background measurements revealed that secondary gamma rays produced from the interaction between neutrons from deuteron fusion reactions and materials surrounding the detector modules were the primary source of background radiation. Based on this background study, the net spectrum of each detector was obtained by subtracting the evaluated background component according to the shape of the background spectrum. Time tracing of neutral particles was obtained by subtracting the evaluated background from the measured neutron flux. Ultimately, neutral energy spectra of H and D are obtained. These results confirm that the E//B NPA is reliably applied for the fast ion detection and neutral flux measurement on the HL-3 tokamak.

This paper presents a technique for mass spectrometry of an ionized cluster flow in the variant of its ionization in a supersonic nozzle when gas flows into a rarefied space. The purpose of the implementation of the methodology presented in the work is its further use for conducting research on the initiation of intracluster energy exchange. To ionize the gas flow in the nozzle, a scheme for generating an effective discharge directly in the diffuser part of a supersonic nozzle has been developed and implemented. The results obtained under the conditions of traditional mass spectrometry of neutral fluxes with particle ionization directly in the mass spectrometer detector (EBMS method) and under the conditions of ionization of a supersonic jet at a selected distance from the nozzle by a high-voltage electron beam (HVEB method) are compared with the results obtained by the discharge ionization method in the nozzle (DIN method). It has been experimentally revealed that when using the DIN method, a significantly larger number of ions are formed than when using the HVEB method, which is an undoubted advantage of the developed method. It is shown that the heating of the nozzle leads to some delay in the condensation process, but a relatively small correction of the stagnation pressure compensates for this loss. The results of trial experiments on the search for conditions for ion-cluster energy exchange are presented using the example of an argon-methane mixture flow.

Ruthenium (Ru) films have recently received attention in the microelectronics industry due to their unique physical and chemical properties. In this work, we investigated etching of Ru using an approach that combines surface functionalization using the effluent of a remote plasma source (RPS) fed with Ar/O2/Cl2 gas mixtures and electron beam (EB) irradiation. Simultaneous exposure of the Ru substrate to reactive fluxes from the RPS and the energetic EB source exhibits a synergistic effect: For combined fluxes, the Ru etch rate (ER) is greater than for separate RPS exposure or EB irradiation. The RPS generates reactive neutral species that functionalize the Ru surface through oxidation and chlorination. The flux of energetic (1 keV) electrons incident on the Ru surface induces Ru etching. A parametric study in which the electron flux density [proportional to the electron emission current (EC)], relative Cl2 and O2 flow rates, and RP power were varied was performed to examine the impacts of the neutral and electron fluxes on the Ru ER. The Ru etching reactions change from being electron flux-limited for small EC to neutral flux-limited etching for large EC or for small reactive gas flows. We also show that selective removal of Ru over Ta, which is important for applications like extreme ultraviolet photomask repair, can be realized for these process conditions. For energetic EB bombardment and Ar/O2/Cl2 RP exposure, a Ru/Ta etching selectivity of ∼6 can be realized. Spatially resolved x-ray photoelectron spectroscopy (XPS) has been performed to characterize the surface chemistry for (a) locations exposed to both reactive neutral and energetic electron fluxes and (b) areas only exposed to the reactive neutral flux produced by the RPS. The XPS results support an EB and RP induced Ru etching mechanism where Ru etching is based on the formation of volatile Ru-oxides, and in which the role of Cl is to assist in Ru oxidation. A surface etching model based on the consideration of the incident oxygen and chlorine fluxes, Langmuir adsorption limited surface functionalization, and EB bombardment causing volatilization of RuO4 in the etching process has been developed. The model can successfully account for the major parametric observations of the Ru ER seen for the energetic EB irradiation and RPS-generated reactive neutral-induced etching process.

Abstract One dimensional fluid/electron Monte Carlo simulations of capacitively coupled Ar/O2 discharges driven by sawtooth up voltage waveforms are performed as a function of the number of consecutive harmonics driving frequencies of 13.56 MHz, N (1–3), pressure (200–500 mTorr) and gas mixture (10%–90% admixture of O2 to Ar). The effects of these external parameters on the electron dynamics, and the transport of ions and neutrals are revealed at constant peak-to-peak driving voltage. The electronegativity is found to decline as the number of consecutive harmonics increases and the DC self-bias voltage decreases. Increasing the pressure also leads to a decrease in electronegativity. The combination of a decrease in the mean free path of electrons and the presence of the electrical asymmetry effect result in different spatio-temporal distributions of the ionization rate, which lead to a reduction in the amplitude of the DC self-bias at higher pressure. As the admixture of electronegative O2 increases, the electronegativity is enhanced, and the discharge mode changes from an α—drift ambipolar (DA) hybrid to DA mode. This work focuses on linking these fundamental changes of the plasma physics induced by changing external parameters to process relevant charged particle and neutral fluxes to the electrodes. Particular attention is paid to O(1D) flux, because it is a precursor of deposition. In discharges driven by sawtooth up voltage waveforms, placing the substrate on the grounded electrode and increasing the number of consecutive harmonics, N, can facilitate the deposition process, since the O(1D) flux to the substrate is higher in these scenarios. Moreover, at an O2 admixture of 20%, the O(1D) flux is nearly as high as that at an O2 admixture of 90%, indicating that a higher O(1D) flux can be achieved without excessively increasing the O2 admixture.

Patterning of ruthenium (Ru) in the microelectronics industry has become important because of novel Ru applications, including back-end-of-line metallization. Selective etching and deposition of Ru over tantalum (Ta) are crucial for the repair of extreme ultraviolet photomasks. A further challenge is to reduce near-surface damage and interdiffusion at the interfaces of material layers, which is often generated when patterning is performed by ion bombardment. In this work, we investigated the etching of Ru and Ta by exposure to electron beam (EB) irradiation and reactive neutral fluxes provided by a remote plasma source (RPS) fed with Ar/O2 gas mixtures. A synergistic effect is observed for Ru etching for simultaneous EB and remote plasma (RP) exposure as compared to isolated EB using the nonexcited feed gas mixture or RP exposure. The RP exposure functionalizes the Ru surface by oxidizing the Ru to nonvolatile RuO2, and the electron flux can further oxidize the functionalized surface to volatile RuO4 resulting in Ru etching. The Ru etch rate (ER) shows strong dependence on O2 flow and EB emission current, which determine the oxygen neutral and electron fluxes to the Ru surface, respectively. The effect of increasing O flux by adding a small amount of CF4 to the Ar/O2 as a feed gas for RPS does not directly result in Ru ER improvement. This is likely due to the formation of nonvolatile Ru oxyfluoride, which cannot be removed by the electron flux for Ar/O2/CF4 gas mixtures. Following Ar/O2/CF4 remote plasma exposure, Ru etching with Ar/O2 is subsequently enhanced for some time once the CF4 flow is stopped. This effect is likely caused by the passivation of reactor walls by RP-generated fluorocarbon species and reduced recombination of reactive oxygen species necessary for Ru etching on the reactor walls, thus leading to a higher ER. Exposure of Ta to EB and Ar/O2 RPS generated fluxes induces oxidation of Ta to nonvolatile Ta oxide, which is accompanied by an increase in layer thickness. The Ta oxidation rate decreases as the Ta oxide layer grows. With the addition of CF4, RP only exposure induces Ta etching by the formation of volatile Ta fluoride, whereas with EB irradiation, Ta oxide forms. Utilizing the passivation effect induced by CF4 addition and the differing responses of Ru and Ta to EB irradiation, we developed a process that enables selective removal of Ru over Ta. Surface chemistry and thickness measurements by spatially resolved x-ray photoelectron spectroscopy and ellipsometry suggest that the EB-induced materials’ modification likely arises from the promotion of surface oxidation.

Abstract Coastal wetlands are one of the most productive ecosystems on Earth with the capacity to sequester large amounts of carbon dioxide (CO2). Wetland loss due to anthropogenic and natural causes reduces the carbon (C) storage capacity and potentially releases previously fixed C in biomass and soil to the water column and atmosphere through decomposition. Coastal wetland restoration has the potential to mitigate some of the C losses depending on the balance of C fluxes. However, the role of vegetation and environmental conditions in governing rates of C accumulation in restoration sites is not well resolved. The purpose of this study was to examine seasonal C fluxes, specifically, gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE) of CO2 in unvegetated and vegetated (Spartina alterniflora) areas of a 2‐year old created marsh, and S. alterniflora and Spartina patens communities in a “natural” reference brackish marsh. S. alterniflora‐dominated areas were sinks for CO2 in both the newly created and reference marsh with an average CO2 uptake rate of 7.0 ± 1.0 μmol m−2 s−1. The unvegetated areas in the newly created marsh and S. patens areas in the reference marsh had approximately net neutral CO2 fluxes. S. alterniflora areas of the created marsh had similar carbon fluxes to that in the reference marsh, despite a much lower soil organic matter content. Because vegetation develops much faster than soil properties, restored marshes can be a C sink equivalent to natural marshes as soon as the marsh is vegetated. Ecosystem productivity and C assimilation in S. alterniflora areas of the reference marsh were enhanced by lower elevations (up to 6 cm) and higher soil bulk density (up to 0.28 g cm−3). At similar elevations, S. alterniflora in both the created and reference marshes was a greater C sink than S. patens areas of the reference marsh. Our findings illustrate that establishment of vegetation is critical to promoting C sink functions in created marshes and, notably, species do matter.

High radiation resistance, chemical inertness, the ability to operate at elevated temperatures, high mobility and efficiency of charge-carrier collection are important properties of diamond for designing detectors and spectrometers of ionizing radiation. Currently, diagnostics of neutrons and neutral particle fluxes based on diamond detectors for the ITER thermonuclear reactor are justified and developed. This work presents the results of a Raman spectroscopy and photoluminescence spectroscopy study of the electronic quality of synthesized epitaxial diamond films obtained by vapor deposition in a hydrogen and methane mixture in the ARDIS reactor on boron-doped single-crystal diamond substrates. To confirm their electronic quality, detectors have been made from films selected by spectrometric methods and the charge collection efficiency and energy resolution have been measured when irradiated with alpha particles from a 241Am source and 14.7 MeV fast neutrons from the ING-07T2 neutron generator.

Abstract The highly radiating nitrogen-seeded H-mode plasmas in unfavorable BT has been characterized in the ASDEX Upgrade tokamak (AUG). Three levels of nitrogen puffing rates have been injected into a fully detached H-mode plasma, which is run in lower single null configuration with the ion B × ∇ B drift away from the X-point. A cold ( ∼ 1 − 2 eV) highly radiating ( ∼ 13.0 MW m − 3 ) region forms close to the X-point immediately after nitrogen seeding, as evidenced by measurements of the divertor Thomson scattering (DTS) and the two-dimensional bolometry reconstructions. In addition, the radiator moves further upwards above the X-point along the separatrix at the high-field side (HFS) with increasing nitrogen puffing rates, as evidenced by the Absolute eXtended UltraViolet (AXUV) measurements. The formation of the highly radiating regime is closely correlated to the modifications of the divertor plasma conditions. Along the line of sight of the DTS measurement, the electron temperature reduces down to a few eV, which initials near the X-point and further extends to the HFS scrape-off layer (SOL) simultaneously with the upward movement of the radiator, however, the electron temperature sustains ( ∼ 30 − 50 eV) at the low-field side (LFS) SOL with slightly decreased electron density. The highly radiating regime shows LFS/HFS divertor asymmetry, in contrast to that for H-mode plasmas in favorable BT , suggesting that the drifts play an important role for the formation of the highly radiating X-point regime at AUG. The neutral particle flux increases significantly (factor of ∼ 2 ) in the private flux region, while it increases slightly ( < 20 % ) in the main chamber, thus suggesting an enhanced sub-divertor neutral compression with the formation of the highly radiating regime. Furthermore, a degradation of the pedestal electron density was observed with an enhancement of the electron temperature further inside the pedestal, and complete divertor detachment was achieved by nitrogen seeding with sustained plasma confinement. Finally, particle sources and flow patterns of deuterium and nitrogen ions have been analyzed by SOLPS-ITER modelling, confirming that the E × B drift plays an important role for the formation of the highly radiating regime in unfavorable BT at AUG.

Ionization of copper in gas and gasless modes of continuous high-power magnetron sputtering

The DIII-D tokamak has elucidated crucial physics and developed projectable solutions for ITER and fusion power plants in the key areas of core performance, boundary heat and particle transport, and integrated scenario operation, with closing the core-edge integration knowledge gap being the overarching mission. New experimental validation of high-fidelity, multi-channel, non-linear gyrokinetic turbulent transport models for ITER provides strong confidence it will achieve Q ⩾ 10 operation. Experiments identify options for easing H-mode access in hydrogen, and give new insight into the isotopic dependence of transport and confinement. Analysis of 2,1 islands in unoptimized low-torque IBS demonstration discharges suggests their onset time occurs randomly in the constant β phase, most often triggered by non-linear 3-wave coupling, thus identifying an NTM seeding mechanism to avoid. Pure deuterium SPI for disruption mitigation is shown to provide favorable slow cooling, but poor core assimilation, suggesting paths for improved SPI on ITER. At the boundary, measured neutral density and ionization source fluxes are strongly poloidally asymmetric, implying a 2D treatment is needed to model pedestal fuelling. Detailed measurements of pedestal and SOL quantities and impurity charge state radiation in detached divertors has validated edge fluid modelling and new self-consistent ‘pedestal-to-divertor’ integrated modeling that can be used to optimize reactors. New feedback adaptive ELM control minimizes confinement reduction, and RMP ELM suppression with sustained high core performance was obtained for the first time with the outer strike point in a W-coated, compact and unpumped small-angle slot divertor. Advances have been made in integrated operational scenarios for ITER and power plants. Wide pedestal intrinsically ELM-free QH-modes are produced with more reactor-relevant conditions, Low torque IBS with W-equivalent radiators can exhibit predator-prey oscillations in T e and radiation which need control. High-β P scenarios with q min > 2, q 95–7.9, β N > 4, β T–3.3% and H 98y2 > 1.5 are sustained with high density ( n¯ = 7E19 m−3, f G–1) for 6 τ E, improving confidence in steady-state tokamak reactors. Diverted NT plasmas achieve high core performance with a non-ELMing edge, offering a possible highly attractive core-edge integration solution for reactors.

ABSTRACT The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift-scan interferometer designed to map the entire northern sky every 24 h. The all-sky coverage and sensitivity to neutral hydrogen flux at intermediate redshifts makes the instrument a resource for other exciting science in addition to cosmology for which it was originally designed. Here, we demonstrate its utility for the study of the H i content of galaxy populations across environments and redshifts. We use simulated data from the IllustrisTNG project to generate mock CHIME-like intensity maps, which we cross-correlate with various tracers – including galaxies and galaxy clusters – to recover aggregate H i signals from stacking analyses. We find that there is more flux in stacks on galaxy clusters or cluster member galaxies compared to those on a general galaxy catalogue due to the enhanced number of H i-rich sources included in the CHIME primary beam. We report that it is possible to infer an average $M_\mathrm{HI}$ for clusters as a function of redshift and selection criteria from the signal in their averaged stacks despite the instrument’s low spatial resolution. This proof-of-concept result opens up a promising, and timely, new avenue to measure the evolution of the neutral hydrogen content in intermediate-to-high redshift galaxy clusters via cross-correlation of galaxy cluster catalogues with 21-cm intensity maps.

A characterization of plasma parameters and neutral particle energies and fluxes has been performed for radio frequency and microwave discharges in the Toroidal Magnetized System (TOMAS). A movable triple Langmuir probe was used to study the electron densities and temperatures, and a time-of-flight neutral particle analyzer was used to measure the energy and fluxes of neutral particles, as a function of the total injected power and the antenna frequency used to generate the plasma. The experimental results can provide information on the behavior of neutral particles at low energies in wall conditioning plasmas.

Abstract Simulations are conducted on capacitively coupled Ar/O2 mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo (MC) model. The research explores the impact of different O2 ratio and pressures on the discharge characteristics of Ar/O2 plasma. At a fixed Ar/O2 gas ratio, with the increasing pressure, higher ion densities, as well as a slight increase in electron density in the bulk region can be observed. The discharge remains dominated by the drift–ambipolar (DA) mode, and the flux of O(3P) at the electrode increases with the increasing pressure due to higher background gas density, while the fluxes of O(1D) and Ar* decrease due to the pronounced loss rate. With the increasing proportion of O2, a change in the dominant discharge mode from α mode to DA mode can be detected, and the O2-associated charged particle densities are significantly increased. However, Ar+ density shows a trend of increasing and then decreasing, while for neutral fluxes at the electrode, Ar* flux decreases, and O(3P) flux increases with the reduced Ar gas proportion, while trends in O(1D) flux show slight differences. The evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport properties. Hopefully, more comprehensive understanding of Ar/O2 discharge characteristics in this work will provide a valuable reference for the industry.

Imbalances in lipid storage and secretion lead to the accumulation of hepatocyte lipid droplets (LDs) (i.e., hepatic steatosis). Our understanding of the mechanisms that govern the channeling of hepatocyte neutral lipids towards cytosolic LDs or secreted lipoproteins remains incomplete. Here, we performed a series of CRISPR-Cas9 screens under different metabolic states to uncover mechanisms of hepatic neutral lipid flux. Clustering of chemical-genetic interactions identified CLIC-like chloride channel 1 (CLCC1) as a critical regulator of neutral lipid storage and secretion. Loss of CLCC1 resulted in the buildup of large LDs in hepatoma cells and knockout in mice caused liver steatosis. Remarkably, the LDs are in the lumen of the ER and exhibit properties of lipoproteins, indicating a profound shift in neutral lipid flux. Finally, remote homology searches identified a domain in CLCC1 that is homologous to yeast Brl1p and Brr6p, factors that promote the fusion of the inner and outer nuclear envelopes during nuclear pore complex assembly. Loss of CLCC1 lead to extensive nuclear membrane herniations, consistent with impaired nuclear pore complex assembly. Thus, we identify CLCC1 as the human Brl1p/Brr6p homolog and propose that CLCC1-mediated membrane remodeling promotes hepatic neutral lipid flux and nuclear pore complex assembly.

The present work presents a 2D and 3D modeling of the neutral gas flow in the sub-divertor region of the W7-X. The investigations have been done using the DIVGAS code. The complex 2D and 3D geometries of the divertor components in the sub-divertor region have been considered and the Standard and High-Iota magnetic configurations have been numerically simulated. The main objective of this study is to investigate the dynamics of neutral particles in the sub-divertor region including the effects due to geometry and toroidal and poloidal leakages located at the divertor targets and baffles on the achieved pumping efficiency. A sensitivity analysis has been performed for the effect of various geometrical and flow parameters on the pumping performance, under different plasma scenarios. The considered incoming fluxes in the sub-divertor range between 1020 to 1022 (H2 s−1). The main conclusions, which can be extracted from the present numerical analysis could be summarized as follows; a large fraction of incoming neutral particle flux i.e. >70% on the low iota side and >40% for the high iota side is leaked back to the main divertor region, while higher incoming neutral fluxes facilitate the increase of the pumped flux as well as the decrease of the outflux. It has been estimated that a small fraction ∼3%–4% of the incoming neutral flux is being pumped via the turbo-molecular pumps. The closure of the toroidal leakages as well as the inclination of the pumping gap panel by 9o facilitate the increase of the pumped flux, but considering the all the engineering constraints, the latter option seems to be more easy to be implemented. For low incoming neutral fluxes (∼1020 H2 s−1) and for the case of AEH section, free molecular flow conditions are estimated and therefore neutral-neutral collisions could be neglected. For higher incoming neutral fluxes and for both AEH and AEP sections neutral-neutral collisions play a significant role in the flow establishment. A comparison with available experimental measurements of the neutral pressure in the sub-divertor has been performed for Standard and High-Iota plasma discharges. The 3D DIVGAS simulations predict qualitatively the experimental data with relative deviation between 25 and 63%. All the above numerical findings will actively support the optimization of the W7-X particle exhaust, in view of the experimental campaign OP2.

Atomic layer etching (ALE) schemes are often deemed economically unviable due to their slow pace and are not suited for every material/hard-mask combination. Conversely, plasma etching presents pattern profile challenges because of its inability to independently control ion and neutral flux. In this work, we introduce a new cyclic transient-based process, called transient-assisted plasma etching (TAPE). A cycle of TAPE is a short exposure step to a sustained flow of reactant before the reactant gas injection is stopped in the second step, resulting in a plasma transient. As the plasma ignites and a substantial amount of etchant remains, a chemically driven etching process occurs, akin to conventional etching. Later in the transient, the modified surface is exposed to a reduced etchant quantity and a sustained ion bombardment, in a similar way to ALE. The cointegration of conventional etching and atomic layer etching allows interesting compromises between etch control and processing time. Going for a transient plasma allows to provide the time and conditions needed for the necessary plasma-surface interactions to occur in one step. In this perspective, the mechanisms behind etch rate, profile correction, and conservation of surface composition using amorphous carbon, as a benchmark, are discussed.