Strike Point Research Articles

Plasma fluctuations in the scrape-off layer and at the divertor target in Alcator C-Mod and their relationship to divertor collisionality and density shoulder formation

Abstract Experiments indicate that the formation of density shoulders in the far scrape-off layer (SOL) is associated with an increase in cross-field transport and the propagation of coherent structures of high density known as blobs. It has been suggested that far SOL divertor collisionality (Λdiv) may be a controlling parameter in this physics, which could be challenging for heat flux mitigation schemes. At Alcator C-Mod, a new high spatial resolution divertor Langmuir probe array (rail probes) combined with a scanning Mirror Langmuir probe has been used to investigate this phenomenon in detail. Experiments were performed to mitigate divertor heat flux and thus increase Λdiv by two different methods and observe the divertor and scrape-off layer plasma response: (1) a 3-point density scan is found to increase the fluctuation intermittency at both the midplane and divertor, and produce a density shoulder at elevated Greenwald fraction; (2) a 3-point N2 seeding scan is found to increase the divertor strike point collisionality, by over two orders of magnitude yet no noticeable trend is observed in either the density profile or the fluctuation statistics. It is concluded that Λdiv near the strike point is not by itself a controlling parameter for SOL fluctuations and shoulder formation which is important for localized heat flux mitigation schemes targeting the strike point where heat flux is the greatest.

Evidence of near-SOL tungsten accumulation using a far-SOL collector probe array and OEDGE modelling in the DIII-D metal rings L-mode discharges

Abstract Experimental evidence is presented of near-scrape off layer (SOL) tungsten accumulation near the crown of lower single-null L-mode discharges in the DIII-D Metal Rings Campaign, based on a peripheral-SOL collector probe (CP) array and OEDGE modelling. Such accumulation has been long-theorized due to parallel force balance in the SOL dominated by the ion temperature gradient force [ 1 , 2 ] but direct experimental evidence has been lacking. Impurity accumulation at this location is undesirable since it largely sets the boundary condition for impurity levels in the confined plasma. Toroidally symmetric rings of 5 cm wide tungsten-coated tiles were installed in the outer divertor of DIII-D. A CP array having multiple-diameter, dual-facing collector rods with axes in the radial direction, was inserted into the peripheral-SOL near the outer midplane to measure the plasma W content. In many cases, more W was deposited on the largest rod on the side facing toward the inner target along the field lines, despite the location of the W source being at the outer divertor strike point. Interpretation of the W deposition profiles on the CP rods support the long-theorized impurity accumulation hypothesis; however, more definitive conclusions will require further experimentation and modelling effort.

Progress of the EU activities for the ITER Divertor Inner Vertical Target procurement

F4E undertook the qualification of so-called “additional suppliers” in order to enhance competition among the potential bidders and to secure the procurement of the ITER Divertor Inner Vertical Target. In order to assess the performances of W armoured plasma facing components under the conditions expected in the divertor target strike point region, a total of 36 W monoblock mock-ups were manufactured by Atmostat (F) by diffusion bonding, and by CNIM (F) and Research Instruments GmbH (D) by brazing, from which fifteen mock-ups were High Heat Flux (HHF) tested at IDTF (Efremov Institute Saint Petersburg, Russian Federation) electron beam test facility.The basic HHF testing program foresaw the performance of 5000 cycles at 10 MW/m2and 300+700 cycles at 20 MW/m2. The test results showed some significant improvements, in particular on the issues of W monoblocks macro-cracking and heat sink thermo-mechanical fatigue performances, identified during previous HHF tests campaigns. Some enhanced HHF thermal fatigue testing and critical heat flux experiments were also performed.

Female Sufi Leaders in Turkey: Signals of A New Social Pattern Emerging in Secular Side

Two sufi women take part in activities related to sufism and create an attraction point in the secular side in Turkey. The most striking point is that both women do not wear headscarves although they are muslim women. This article attempts to show how sufi women Cemalnur Sargut and Hayatnur Artiran have idealized a Muslim woman's identity, the work they are doing to achieve this ideal, their attidue toward Rebublic values, and the effects of these attitudes on their followers. This article was created from my doctoral thesis and based on Qualitative research which has been established on the basis of 2-year long participant observation and data obtained from in-depth and focus interviews. 31 women and 20 men were interviewed in depth and focus interviews. The main conclusions of my qualitative research are that the influence of theese sufi women is related with process of modernization by accelerating the establishment of the republic in Turkey. It seems that a perception has established concerning that “public apparency’’ of woman will disappear if the “apparency of body’’ disappears and the woman will return to its role which had relapsed into silence for centuries. Besides not using the headscarf, religious conversation has been created by these sufi women in the balance of religion, philosophy and science and the fact that they are conducting their works under secular institutions such as foundations and associations have also been observed to have a very important effect on secular side.

Heat flux distribution with lower hybrid current drive in the experimental advanced superconducting tokamak

Lower hybrid current drive (LHCD) considerably affects the heat flux distribution. This study analyzed the lower divertor target plate (LDTP) with different LHCD powers and frequencies in the experimental advanced superconducting tokamak (EAST). The analysis provided a detailed explanation of the heat flux at specific times (i.e., transformation of magnetic field configuration, LHCD starting and operating periods) and specific target locations (i.e., original strike point and second peak heat flux area). The average heat flux, average peak heat flux, and maximum peak heat flux during operation of different LHCD powers and frequencies were determined and compared. The sizes of the heat fluxes at the specific target locations were compared at different LHCD powers and frequencies. In addition to the heat flux distribution under different LHCD powers and frequencies, the heat flux distributions in electron cyclotron resonance heating (ECRH) + LHCD and in LHCD only were investigated to study the effect of ECRH on heat flux distribution. Detailed analyses of the heat flux distribution under different conditions were conducted to provide a reference for actual engineering applications.

Comparing N versus Ne as divertor radiators in ASDEX-upgrade and ITER

Abstract The study aims to estimate the influence of machine scale size on the behavior of plasma with extrinsic seeded impurities in the scrape-off layer (SOL) and divertor. This is performed through the comparison of plasma boundary simulations using the SOLPS-ITER code including drifts and currents of nitrogen (N) and neon (Ne) injection in ITER and ASDEX Upgrade (AUG) geometries. Trends are examined between the two seeding species in each individual device and by a comparison of the differences between the two machines. In the modeling results, the radiated power peak is located near the X-point in the inner divertor for the AUG cases and in the vicinity of the strike points in both divertors in ITER. The simulations also find less Ne impurity ions in the divertor volume than N and more significant Ne radiation inside the separatrix for AUG, consistent with published experimental findings. In ITER, both species radiate mostly from the divertor, in agreement with the existing SOLPS-4.3 simulation database obtained without drifts and with a less sophisticated treatment of parallel impurity transport. Drifts are important players in determining the plasma background for AUG and are comparatively less important in ITER. In both devices, the spatial distribution of the impurity ion density is complex, with their parallel flow patterns correlating with the thermal and friction force balance. Within this isolated modeling study, the principal reasons for different behavior between N and Ne on AUG and ITER appear to be the combination of a stronger drift effect and reduced screening of recycled fuel and impurity from divertor to private flux region on AUG leading to a more extended, colder plasma than in ITER. The increased temperature in the confined region just inside the separatrix on ITER also means that impurity ions reaching this zone are fully ionized and do not contribute significantly to the radiation loss there. On the basis of this study, both N and Ne are found to be acceptable low Z radiators on ITER.

Electromagnetic effect of lightning return stroke to buried energy pipelines

Direct lightning strike in the vicinity of buried high-pressure energy pipeline can cause damages to pipe coatings or to the metal pipe. This damage sometimes leads to explosions which may cause loss of consignments. This is also a risk to pipeline integrity and safety of the people working on the pipeline. Hence, lightning induced electromagnetic interference (EMI) on buried energy pipeline is a matter of serious concern. To protect buried metallic energy pipeline from the effects of direct lightning strikes near the pipeline to the ground, it is necessary to have comprehensive information about the lightning currents and the radiated electromagnetic fields. To obtain thorough information of lightning-induced effect on the buried pipeline, a computational model considering electrical parameters of soil, pipe and lighting strikes to carry out a simulation of buried pipeline under soil has been developed which can be used to identify parameters influencing the coupling phenomenon between pipeline and lightning strike. The E and H field was estimated at various distance and depth from the point of strike. The model is based on the finite difference time domain (FDTD) solution of Maxwell’s equations. Lightning current and other fields are calculated within soil with and without the presence pipe and the same has been done for pipe with and without corrosion coating. The results are then used to analyze the influence of various parameters of the studied system on the development of high breakdown potential around the pipeline. This paper then presents the impacts of the direct lightning strike to the ground on buried metallic energy pipeline with corrosion coating. The results showed that although ground conductivity, current rise time, burial depth of pipeline and the pipeline metallic property has an influence on the severity of impact, in case of coated pipe, the coating on pipeline plays a great role on the scale of impact lightning can cause on the pipeline. While coating prevents pipelines from corrosion, the very low conductive coating is also responsible for very high electric field above the pipe surface. This work will be very useful pipeline industry in selecting a coating with suitable impedance value so that buried pipeline can be protected from both corrosion and lightning strike.

Effect of cross-section shape of rotating chute on particle movement and distribution at the throat of a bell-less top blast furnace

Rotating chutes are widely used to control the burden distribution and enhance the gas distribution in a blast furnace. The chute cross-section shape has a significant effect on the particle movement and distribution. Therefore, this study developed a three-dimensional model of a blast furnace top with rotating chute using the discrete element method. The effect of different chute shapes on the particle movement and radial burden distribution was then investigated. The results showed that the burden stream height at the chute discharge agrees well with the burden stream thickness at the burden surface. A semicircular chute had the largest main striking point, where the chute discharge joins the burden surface, and trapezoidal and rectangular chutes had successively smaller MSPs. The semicircular chute helped to obtain a uniform radial size distribution. The trapezoidal chute helped form an aggregated burden stream at low rotating speeds, while the rectangular shape chute achieved this at higher rotating speeds and different chute angles.

First heat flux estimation in the lower divertor of WEST with embedded thermal measurements

The present paper deals with the surface heat flux estimation with thermocouples (TC) and fiber Bragg grating (FBG) embedded in the plasma facing components (PFC) of the WEST tokamak. A 2D heat transfer model combined with the conjugate gradient method and the adjoint state is used to estimate the plasma heat flux deposited on the PFC. The plasma heat flux is characterized by the time evolution of its amplitude and spatial shape on the target (heat flux decay length λqt, power spreading in the private flux region St and the strike point location x0). As a first step, five ohmic pulses have been investigated with different magnetic configuration and divertor X-point height varying from 44 to 68 mm from the surface. Despite an outboard shift, the relative displacements of the outer strike point as well as the heat flux decay length derived from the TC/FBG systems are consistent with the magnetic equilibrium reconstruction.

Observation of modified divertor particle flux with coherent modes in KSTAR edge plasma

The coherent modes in the edge plasma density of KSTAR high confinement mode plasma are found to affect the particle flux incident on the divertor. These coherent modes are synonymous with inter-edge-localized filamentary modes. The coherent structures that typically fall inside the fast toroidal rotation zone or toroidal rotation shear zone, undergo distortion and elongation followed by either breakage or significant modulation in the scrape-off layer (SOL) transport, possibly leading to the observed coherent fluctuations on the divertor slightly further (outward) from the outer strike point. The distorted coherent structures appear as spatially large sized in the poloidal plane and exhibit long range correlation in the edge plasma, extending into the scrape-off layer in some cases. Further, the elongated structures possibly modify the particle flux at the plasma boundary after their onset, and lead to reduced particle flux close to the outer strike point. The coherent modes that occur with relatively smaller spatial size in the edge plasma density at the foot of the toroidal rotation zone do not show any noticeable modification in the particle flux on the divertor. The growth of coherent structures to a large spatial size and distortion is a possible consequence of the presence of strong toroidal flow or flow shear in the location of coherent modes and/or nonlinear evolution.

Modelling of tungsten erosion and deposition in the divertor of JET-ILW in comparison to experimental findings

The erosion, transport and deposition of tungsten in the outer divertor of JET-ILW has been studied for an H-Mode discharge with low frequency ELMs. For this specific case with an inter-ELM electron temperature at the strike point of about 20 eV, tungsten sputtering between ELMs is almost exclusively due to beryllium impurity and self-sputtering. However, during ELMs tungsten sputtering due to deuterium becomes important and even dominates. The amount of simulated local deposition of tungsten relative to the amount of sputtered tungsten in between ELMs is very high and reaches values of 99% for an electron density of 5E13 cm−3 at the strike point and electron temperatures between 10 and 30 eV. Smaller deposition values are simulated with reduced electron density. The direction of the B-field significantly influences the local deposition and leads to a reduction if the E × B drift directs towards the scrape-off-layer. Also, the thermal force can reduce the tungsten deposition, however, an ion temperature gradient of about 0.1 eV/mm or larger is needed for a significant effect. The tungsten deposition simulated during ELMs reaches values of about 98% assuming ELM parameters according to free-streaming model. The measured WI emission profiles in between and within ELMs have been reproduced by the simulation. The contribution to the overall net tungsten erosion during ELMs is about 5 times larger than the one in between ELMs for the studied case. However, this is due to the rather low electron temperature in between ELMs, which leads to deuterium impact energies below the sputtering threshold for tungsten.

Advances in radiated power control at DIII-D

Feedback control of radiated power from the lower divertor Prad, div, L has been implemented in the DIII-D Plasma Control System (PCS). A realtime sensor for Prad, div, L has been constructed from 12 foil bolometer channels which agrees with standard post-shot analysis to within 20%. Results with the 12-channel sensor are compared to initial proof-of-concept tests with a single channel as a proxy for Prad, div, L, showing that the upgraded sensor is necessary to overcome limitations of the proxy channel strategy in DIII-D. Using N2 seeding under feedback control, Prad, div, L has been increased by up to 150% above unseeded levels, and a radiated power fraction frad of 80% has been demonstrated, although feedback controlled gas flow is steadier at frad = 55%. Spatial coverage is broad enough to enable Prad control during the strike point sweeps which are commonly used to generate pseudo-2D divertor Thomson measurements in DIII-D divertor experiments. Use of this control reveals challenges that may affect next step devices, which will require actively controlled extrinsic impurity seeding in order to manage heat loads. When operating at high frad, changes in pedestal Te (caused by ELMs in these experiments but could come from other disturbances) resulted in large perturbations to Prad which were destabilizing to the feedback controller.

Simulation of Polarising and Reflector Gratings for High Power mm Waves

High power mm waves for fusion plasma heating need to be elliptically polarised to ensure good absorption in the plasma. In some scenarios, electron cyclotron resonance heating (ECRH) at higher harmonics (X3 and O2) is used, but this has significant shine-through because of low single pass absorption. Grating reflectors at the inboard strike point form a holographic mirror that reflects the beam back into the plasma. This paper investigates the optical properties and ohmic losses of both the polariser and the reflectors with the 3D fullwave code IPF-FD3D. The reflection properties of a reflector for ASDEX Upgrade and the improved ohmic losses of a waveguide polariser were confirmed.

Reseña de Cities in global capitalism

El geógrafo italiano, de origen napolitano, Ugo Rossi ha publicado una monografía sobre las ciudades en el capitalismo global en la editorial Polity Press. Tras una brillante labor investigadora, con múltiples artículos en revistas científicas de prestigio, y docente, con estancias en diferentes universidades europeas, desarrollando su labor principal en la de Turín, y estadounidenses, Rossi ha elaborado una magna obra teórica de Geografía Urbana. De hecho, una primera circunstancia que llama la atención es el exclusivo carácter teórico del libro, dado que no hay ni una sola figura o tabla ni tampoco la más mínima cartografía.

A comprehensive analysis of the protein-ligand interactions in crystal structures of Mycobacterium tuberculosis EthR

The Mycobacterium tuberculosis EthR is a member of the TetR family of repressors, controlling the expression of EthA, a mono-oxygenase responsible for the bioactivation of the prodrug ethionamide. This protein was established as a promising therapeutic target against tuberculosis, allowing, when inhibited by a drug-like molecule, to boost the action of ethionamide. Dozens of EthR crystal structures have been solved in complex with ligands. Herein, we disclose EthR structures in complex with 18 different small molecules and then performed in-depth analysis on the complete set of EthR structures that provides insights on EthR-ligand interactions. The 81 molecules solved in complex with EthR show a large diversity of chemical structures that were split up into several chemical clusters. Two of the most striking common points of EthR-ligand interactions are the quasi-omnipresence of a hydrogen bond bridging compounds with Asn179 and the high occurrence of π-π interactions involving Phe110. A systematic analysis of the protein-ligand contacts identified eight hot spot residues that defined the basic structural features governing the binding mode of small molecules to EthR. Implications for the design of new potent inhibitors are discussed.

Evaluation of tungsten influx rate and study of edge tungsten behavior based on the observation of EUV line emissions from W6+ ions in HL-2A

The tungsten spectrum in the extreme ultraviolet (EUV) wavelength range has been investigated in tokamak HL-2A to find line emissions from low-ionized tungsten ions which can be used for tungsten transport study in the plasma edge. For this purpose, tungsten is injected in the HL-2A plasma using the laser blow-off (LBO) technique with a newly developed double-layer tungsten target. The total number of injected tungsten particles can be accurately controlled by adjusting the distance from the focal lens to the tungsten target. A quasi-continuum spectrum called an unresolved transition array (UTA), consisting of many line emissions from several ionization stages of tungsten ions, is observed at around 50 Å as a typical indication of the tungsten spectrum. In the present HL-2A experiment the quasi-continuum of tungsten is mainly composed of line emissions from W14+ to W23+ ions. Analyzing the observed tungsten spectrum, two isolated line emissions of W VII (5p–5d: 216.219 Å) and W VII (5p–5d: 261.387 Å) from W6+ ions are successfully identified for the first time in tokamaks. The intensity ratio and the wavelengths of the two lines determined in the present experiment show good agreement with the intensity ratio calculated with a collisional-radiative model developed for the W6+ ion and a previous result by Sugar and Kaufman (1975 Phys. Rev. A 12 994), respectively. On the other hand, the W VII line emission occasionally reappears after the LBO injection, suggesting a re-entry of the tungsten deposited onto divertor plates and a movement of the strike point during the discharge to a certain area of the divertor plate where tungsten is deposited. Based on the W VII emission observed during the re-entry event of tungsten ions, an influx of the W6+ ion, , to the edge plasma is evaluated using the inverse photon efficiency calculated with the ADAS code and using an average-configuration option. As a result, it is found that is typically within the range (0.1–2.0) × 1013 cm−2 s−1. A brief discussion is also made on the influx evaluated in the present study.

Toroidal variation of the strike point in DIII-D

We report measurements of a+/− 5 mm toroidal variation of the outer strike point radial position using an array of three identical Langmuir probes distributed at 90° intervals around the torus (90°, 180°, 270°). The strike point radial location is determined from the profiles of floating potential (Vf) measured by the three 6 mm diameter domed Langmuir probes as the strike point is swept radially on a horizontal tile surface just outside of the upper small angle slot (SAS1) divertor. Based on the three probe measurements, the strike point variation is consistent with previous error field measurements by Schaffer [1,2] and estimates by Luxon [3] which indicated the strike point error could appear as an n = 1 radial variation of 4.5 mm at the outer mid plane and thus could be effectively described with a three point measurement. The results are also consistent with field line tracing calculations using the MAFOT code [4]. The small angle slot (SAS1) divertor performance is particularly sensitive to a misalignment with the divertor plasma since enhanced neutral confinement and recycling in the slot and distribution of neutrals along the slot surfaces are important for achieving divertor detachment at the lowest possible core plasma separatrix density. These strike point measurements are discussed with regard to the slot divertor alignment.

The effect of the secondary x-point on the scrape-off layer transport in the TCV snowflake minus divertor

The snowflake (SF) magnetic configuration is investigated as a potential power exhaust solution for a fusion reactor, but also to improve our understanding of divertor physics in general. Unlike a conventional single null (SN), it features an additional nearby x-point, which deeply modifies the magnetic field in the scrape-off layer (SOL) and can thereby affect parallel and cross-field transport of heat and particles. This paper investigates the power exhaust properties of the snowflake minus (SF-) configuration on the TCV tokamak, for Ohmically heated, L-mode, low-density, attached plasmas for a range of x-point separations, magnetic field directions and locations of the secondary x-point (low-field-side (LFS) or high-field-side (HFS)). Due to the relatively large x-point separation in physical space, this study probes x-point transport features in general, rather than reactor relevant aspects of the SF configuration. The target heat fluxes at all strike points are simultaneously monitored with an infrared (IR) thermography system and the kinetic profiles of the SOL at the outer mid-plane with a reciprocating probe (RCP). The placement of the additional x-point is seen to affect the inner-outer divertor power balance. An effective heat flux width for the SOL in the low poloidal field region is inferred from the measured power repartition between the two SOL manifolds created by the secondary x-point. For the LFS SF- configuration (secondary null in the LFS SOL), the is two times larger than that measured by the RCP at the outer mid-plane and by IR at the outer target of a comparable SN, while the outer mid-plane SOL profiles are similar to the SN. This is interpreted as the effect of increased effective cross-field diffusivity in the intra-null region relative to the rest of the SOL. For the HFS SF- configuration (secondary null in the HFS SOL), no such increased transport is observed. The pressure-driven plasma convection expected near the primary null cannot explain the increased , which is instead consistent with interchange ballooning-like turbulence enhanced by the low poloidal field.

Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall

Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analysed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 μm were indicated, but typical values were on the order of a few hundred nm. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 μm were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas

The experimentally observed in/out detachment asymmetry in KSTAR L-mode plasmas with deuterium (D) fueling and carbon walls has been investigated with the SOLPS-ITER code to understand its mechanism and identify important atomic processes in the divertor region. The simulations show that the geometrical combination of a vertical, inner target with a short poloidal connection from the X-point to the target and a much longer outer divertor leg on an inclined target lead to neutral accumulation towards the outer target, driving the outer target detachment at lower upstream density than is required for the inner target. This is consistent with available Langmuir probe measurements at both target plates, although the inner target profile is poorly resolved in these plasmas and further experiments with corroborating diagnostics are required to confirm this finding. The pressure and power loss factors defined in the two-point model (Stangeby 2018 Plasma Phys. Control. Fusion 60 4; Kotov and Reiter 2009 Plasma Phys. Control. Fusion 51 115002; Stangeby and Sang 2017 Nucl. Fusion 57 056007; Moulton et al 2017 Plasma Phys. Control. Fusion 59 6) of the divertor scrape-off layer (SOL) and the sources contributing to the loss factors are calculated through post-processing of the SOLPS-ITER results. The momentum losses are mainly driven by plasma-neutral interaction and the power losses by plasma-neutral interaction and carbon radiation. The presence of carbon impurities in the simulation enhances the pressure and power dissipation compared to the pure D case. Carbon radiation is a strong power loss channel which cools the plasma, but its effect on the pressure balance is indirect. Reduction of the electron temperature indirectly increases the momentum loss and increasing the volumetric reaction rates which are responsible for the loss of momentum. As a result, the addition of carbon saturates the momentum and power losses in the flux tube at lower upstream densities, reducing the roll-over threshold of the upstream density. The relative strengths of the various mechanisms contributing to momentum and power loss depend on the radial distance of the SOL flux tubes from the separatrix (near/far SOL) and the target (inner/outer target). This is related to the strong D2 molecule accumulation near the outer strike point, which makes the deuterium gas density at the outer target 2–10 times higher than that at the inner target. A large portion of the recycled neutral particles from both targets reach and accumulate in the outer SOL, which is predominantly attributed to the target inclination and gap structure between the central and outboard divertors and hence to the impact of geometry. The accumulated neutrals enhance the reactions involving D2, which causes momentum and power loss.