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REVIEW 3 major objections 6 minor 25 references

SOLPS-ITER Numerical Simulations of ITER-scale Snowflake Divertors: Low-Field-Side SF-/SF+ and High-Field-Side SF-/SF+ Configurations

T0 review · 3 major / 6 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read This paper argues that a low-field-side snowflake-minus divertor with a closed, steeply inclined inner target compresses recycling neutrals into the outer scrape-off layer and private-flux region, producing enough volumetric ionization and

desk verdict First systematic SOLPS-ITER sweep of all four snowflake topologies at ITER scale; the LFS SF- neutral-compression mechanism is coherent but rests on transport coefficients the authors themselves flag as suspect. read the letter →

arxiv 2509.02455 v1 pith:XXQOAAGA submitted 2025-09-02 physics.plasm-ph

H.S. Wu , F. Subba , M.R.K. Wigram , O. Pan , R. Lo Frano , A. Pucciarelli , R. Zanino This is my paper · ORCID
classification physics.plasm-ph PACS 52.55.Fa52.55.Rk
keywords snowflakedivertorSOLPS-ITERdetachmentpowerexhaustneutralrecyclingmagneticgeometrytargettokamakedgeplasma
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper uses the SOLPS-ITER edge-plasma code to simulate all four snowflake divertor topologies at ITER scale and to isolate which magnetic and target geometries actually reduce the heat load on the plates. Its central finding is that the low-field-side snowflake-minus configuration can be made to detach its outer target even at low upstream density: the secondary X-point shortens the distance between the inner and outer strike points, and a closed, steeply inclined inner target then compresses recycling neutrals into the outer scrape-off layer and private flux region, where ionization and recombination dissipate the power before it reaches the plates. In the simulations this drops the outer target surface heat flux to about 2 MW/m2 while a comparable single-null divertor at the same density is only at the onset of detachment. The paper turns this into a concrete design recipe for future devices (minimize the inner-to-outer strike point distance, shape the inner target to compress neutrals, incline the plates, set the X-point separation dxx to about half the local power decay length), and it notes that the plus-topology snowflakes create an ionization/recombination zone between the two X-points that may seed an X-point radiator once impurities are added.

What carries the argument

The load-bearing object is the six-region snowflake topology created by the secondary X-point and the neutral recycling it redirects. In the SF- topologies the secondary X-point splits the scrape-off layer into SOL1 and SOL2 and shortens the field-line distance between the inner and outer strike points (about 1.2 m versus 2 m in the single null); the closed, steeply inclined IT1 target then behaves as a baffle that compresses IT1 recycling neutrals into PFR3 and LFS SOL1. There, ionization and recombination remove energy volumetrically, dropping the local electron temperature and detaching the magnetically connected outer target OT1. The control knob is dxx, the distance between the two X-po

What would settle it

Run the same LFS SF- geometry with turbulence-resolving or enhanced-transport modelling in the private flux region, or measure neutral pressure and recombination in the PFR3/LFS SOL1 channel of a device such as TCV or MAST-U in snowflake-minus discharges: if the outer target fails to detach at the low upstream density simulated here (ncore = 3.0e19 m-3) once PFR transport is resolved, or if the recombination zone in that channel does not appear, the neutral-compression mechanism as quantified would be falsified.

Watch

Extended reading notes

Core claim

In the LFS SF- divertor the secondary X-point shortens the distance between the inner target IT1 and the outer target OT1, so neutrals recycled at IT1 reach PFR3 and LFS SOL1 instead of the high-field side. A closed, highly inclined inner target compresses those neutrals into the outer SOL, where ionization and recombination zones dissipate power volumetrically. OT1 then fully detaches (electron temperature below 2 eV, peak surface heat flux about 2-3 MW/m2, near 30% of the single-null value) already at ncore = 3.0e19 m-3, while a single-null outer target at that density is only near detachment onset. The same mechanism underlies the design strategy, including dxx ≈ 3 mm ≈ ½ λq with local λq

Load-bearing premise

The results stand on the assumption that cross-field turbulent transport is the same everywhere in the edge plasma, including the large private-flux regions where snowflake geometry creates wide, weakly magnetized volumes; the authors themselves flag this as questionable, and the fixed-density core boundary additionally lets particle throughput vary by nearly a factor of two between configurations.

Editorial extensions

If this is right

  • An LFS SF- divertor built to this recipe detaches its outer target at low upstream density, so future reactors could meet outer-divertor heat-flux limits with less reliance on high density or impurity seeding.
  • The X-point separation dxx becomes a practical tuning actuator: increasing it shifts power from IT1 toward OT1 and OT2, so heat load can be balanced across the three outer targets rather than minimized on one.
  • The closed inner target raises the parallel heat flux at IT1 by pushing neutrals out of the high-field-side SOL, but the steep plate inclination compensates, cutting the net surface heat load at IT1 by about half.
  • For SF+ divertors, the ionization and recombination zone between the two X-points, near the primary X-point, is a plausible seed for an X-point radiator, which the authors say requires impurity-seeding simulations to confirm.
  • HFS SF- divertors show the mirror-image behavior (inner targets detach easily with ITER-like plates), and the outer IL plate acting as a baffle suggests combining HFS SF- with a Super-X outer divertor.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The uniform-transport assumption is the most direct stress test: the paper itself cites TCV turbulence measurements and MAST-U churning-mode simulations indicating power redistribution across the private flux region, so a turbulence-resolving simulation of the same LFS SF- geometry could move the detachment threshold to higher density or change which topology performs best.
  • The dxx ≈ ½ λq rule is stated for one device scale; a natural generalization to test is whether the ratio, rather than the absolute 3 mm, survives scans of input power or λq, which would let the rule transfer to other machines.
  • Because comparisons fix core density rather than particle throughput (throughput ranges 1.9-3.5e21 atom/s among configurations at high density), a gas-puff-matched comparison might reorder the configurations while leaving the neutral-compression mechanism itself intact.
  • A simulation that removes the secondary X-point but keeps the closed, inclined target plates (a single-null with the same shaping) would isolate how much of the detachment benefit comes from the snowflake null versus the target geometry alone.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The paper presents SOLPS-ITER simulations of four snowflake divertor configurations (LFS SF−, LFS SF+, HFS SF+, HFS SF−) at ITER scale, using pure deuterium, no drifts, fixed core-density boundary conditions, and both flat and ITER-like target geometries. It reports an upstream density scan spanning low-recycling, high-recycling, and detached regimes; scans of the secondary X-point position (dxx for SF−, σ for SF+); and a comparison of flat versus ITER-like divertor shapes. The central claim is that in the LFS SF− configuration, a closed, highly inclined inner target compresses recycling neutrals from the inner divertor into the PFR3 and LFS SOL1 regions, producing strong volumetric dissipation and full detachment of the outer target OT1 even at ncore = 3×10^19 m^-3, with qsurf ≈ 2 MW/m^2. A design strategy is proposed, including a recommendation of dxx ≈ 3 mm ≈ 1/2 λq. For the SF+ configurations, the paper reports strong ionization and recombination sources near the primary X-point, which it suggests could be relevant to X-point radiator formation.

Significance. If the central result holds, the paper provides a concrete, geometry-based path to outer-target detachment in an ITER-scale snowflake divertor, which is a valuable design input for future devices. The work is also notable as the first SOLPS-ITER study to include HFS SF− and HFS SF+ configurations at ITER scale, and it systematically compares magnetic and target-geometry effects across all four snowflake topologies. The authors are transparent about their modeling limitations, and the claimed secondary X-point power splitting in SF− configurations is consistent with TCV experimental observations, providing some external anchor. However, the main mechanism relies on neutral confinement and recombination in the private flux region, where the model uses uniform transport coefficients that the authors themselves concede may be inappropriate for snowflake divertors. Because no sensitivity tests are presented, the significance is currently conditional on the PFR transport assumption.

major comments (3)
  1. [Section 3, Section 7, Figures 12 and 22] The central detachment mechanism for LFS SF− depends on neutral compression and recombination in PFR3 and near the SOL1/PFR3 interface (Figures 12(h), 22(i-l)). These regions are computed with uniform D_perp = 0.1 m2/s and chi_perp = 0.3 m2/s applied across the whole domain (Section 3), yet Section 7 concedes that applying uniform perpendicular transport coefficients to the large PFRs of SF divertors 'may not be appropriate', citing TCV turbulence studies [43,44] and MAST-U simulations [45] showing enhanced PFR transport. This is a load-bearing modeling premise: an increase in PFR transport would directly modify the ionization/recombination balance and neutral pressure buildup that produces OT1 detachment. The manuscript contains no sensitivity scan or bounding estimate. I request a quantitative test, e.g., a factor 2-3 increase of PFR D_perp/chi_perp or localized X-point-enhanced transp
  2. [Section 4.3, Section 7, Figures 8, 10, 11] The fixed core-density boundary condition leads to a 1.8x spread in particle throughput across the SF configurations at high density (1.9×10^21 to 3.5×10^21 atom/s, Section 7). This is acknowledged, but the cross-configuration comparisons in Section 4.3 (e.g., which targets detach in which configuration) are not throughput-matched. Differences in detachment status and target heat loads may therefore reflect particle throughput rather than magnetic or target geometry. The IL Low density LFS SF− result is a within-configuration comparison and is less affected, but the dxx scan in Section 5.1 and the IL High density comparisons share the issue. Please either repeat key comparisons with matched throughput, demonstrate insensitivity to throughput within each configuration, or at minimum report the throughput for all IL and dxx-scan cases so the reader can assess the ambiguity.
  3. [Section 5.1 and Section 6.1] The proposed design strategy recommends dxx ≈ 3 mm ≈ 1/2 λq, but this value is based on flat-target dxx scans (Section 5.1, Figure 15) combined with IL-geometry simulations performed only at the reference dxx = 2.5 mm (Section 6.1). The combined effect of the IL target shape and dxx optimization is not directly simulated. It is therefore not demonstrated that dxx ≈ 3 mm remains optimal with the closed, inclined inner target, or that the IL target shape does not shift the optimum. Please either simulate the IL geometry for at least two dxx values near the recommended value or explicitly downgrade this recommendation to a hypothesis to be tested in future work.
minor comments (6)
  1. [Abstract and Section 1] The abstract contains typos and encoding artifacts: 'Scape-OƯ Layer', 'serval', 'SOLS-ITER' (should be SOLPS-ITER), and garbled mathematical symbols in the introduction equations. Please correct these and ensure the equation encoding is clean.
  2. [Figure 9 caption] Figure 9 is described as 'OMP profiles ... at the low upstream density condition', but Section 4.3 is the high upstream density case. The caption should say 'high upstream density condition'.
  3. [Figure 25 caption] Figure 25 is captioned 'LFS SF- ITER-like cases' but the section is about LFS SF+; the caption should read 'LFS SF+ ITER-like cases'.
  4. [Figure 28 caption] Figure 28 is captioned 'LFS SF+ ITER-like cases (purple)' but the section is about HFS SF−; the caption should read 'HFS SF− ITER-like cases'.
  5. [Section 3 and throughout] The notation nD+2D2 is awkward; it is used for combined atomic and molecular deuterium density but is introduced only in the caption of Figure 22. Please define it explicitly in the text and use a clearer notation such as n_D + n_D2.
  6. [Section 4.2 and Section 5] Some figure references are inconsistent: Section 4.2 refers to Figure 8 for inner/outer target parameters, while Section 5.1 refers to Figure 14 for power sharing; the text sometimes says 'OT2 and OT3' when the target naming conventions could be confused. Please re-check all cross-references after final typesetting.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the LFS SF- neutral-compression detachment result is an emergent output of a forward SOLPS-ITER simulation, not an input or fitted parameter.

full rationale

The central claim (Section 4.3, Section 6.1) is that in the LFS SF- configuration the closed, highly inclined inner target compresses recycling neutrals into the PFR3/LFS SOL1 regions, enhancing volumetric dissipation and detaching OT1. This is an emergent result of the SOLPS-ITER forward model: the inputs are magnetic equilibria, target geometry, a fixed core density, and uniform transport coefficients, while detachment, recombination zones, and qsurf are solved quantities. No parameter is fitted to the reported qsurf or Te values at OT1, and Eq. (5) is only a definition of qsurf in terms of the computed plasma flux plus surface recombination, not a pre-imposed target value. The transport coefficients D_perp=0.1 m2/s and chi_perp=0.3 m2/s are inherited from prior ASDEX Upgrade work [35][36] by the same group, but that prior work is an externally anchored validation, and the coefficients are not tuned to the snowflake predictions. The paper itself flags in Section 7 that "applying uniform perpendicular transport coefficients for the whole PFRs may not be appropriate," citing TCV turbulence and MAST-U MHD results. That is a genuine modeling-adequacy limitation and a correctness risk, but it is not a circular reduction: the prediction does not reduce to the assumption, it is merely sensitive to it. Similarly, Section 7 acknowledges the fixed-core-density boundary condition leads to throughput variations (1.9e21-3.5e21 atom/s at high density); this is an honest caveat, not a circular step. External anchors exist, e.g., power splitting at the secondary X-point is compared with TCV [11] and the SF+ inter-X-point density zone with EMC3-EIRENE [31]; the paper also reports a genuine mismatch (in-out power sharing remains nearly constant, inconsistent with TCV). The design recommendation dxx ~ 3 mm ~ 1/2 lambda_q is an inductive rule derived from the dxx scan, with lambda_q itself a simulation output; it is not equivalent to the input by construction. No self-definitional, fitted-input-as-prediction, uniqueness-imported, or ansatz-smuggling step is present. Verdict: no significant circularity.

Assumptions & free parameters 4 free parameters · 5 assumptions · 0 invented entities

The central claims rest on the SOLPS-ITER forward model with hand-chosen transport coefficients and simplified neutral and pumping boundary conditions, not on a closed-form derivation. No new physical entities are introduced. The dominant unproven inputs are the uniform PFR transport coefficients and the fixed core-density boundary condition, both flagged by the authors in Section 7.

free parameters (4)
  • D_perp (perpendicular particle diffusivity) = 0.1 m2/s
    Uniform value across the whole plasma domain including the large PFRs of SF divertors; chosen from prior AUG practice and sets the lambda_q ~ 6 mm scale. Authors flag in Section 7 that uniform PFR transport may be inappropriate.
  • chi_perp (perpendicular heat diffusivities) = 0.3 m2/s for ions and electrons
    Uniform across the domain; together with D_perp it determines lambda_q ~ 6 mm, which is used in the design recommendation dxx ~ 3 mm ~ half of lambda_q.
  • Pumping surface albedo = 0.99
    Simplified mimic of pumping. Pumping surfaces are not in identical positions across the four configurations, contributing to the throughput differences acknowledged in Section 7.
  • Input power at core boundary = 20 MW, split equally between electrons and ions
    Chosen input, not fitted; standard for ITER-scale studies. All target heat loads scale with this assumption.
assumptions (5)
  • domain assumption SOLPS-ITER (B2.5-EIRENE) fluid-kinetic edge model is quantitatively adequate for ITER-scale SF divertors with four PFR regions
    The code has been validated on single-null divertors (AUG, JET, ITER design), but applying it to SF divertor geometry with multiple PFRs is an extrapolation that the paper relies on throughout Sections 4 to 6.
  • domain assumption Uniform perpendicular transport coefficients apply in the PFR and across all SF configurations
    Invoked in Section 3; explicitly flagged in Section 7 as potentially inappropriate, with citations to TCV turbulence studies [43][44] and MAST-U MHD simulations [45].
  • domain assumption Fixed core density with albedo-0.99 pumping yields comparable and interpretable conditions across configurations
    Stated in Section 3 as a stability and convergence choice; Section 7 concedes it produces different particle throughputs (1.9 to 3.5e21 atom/s), partially invalidating this assumption for cross-configuration comparison.
  • domain assumption FreeGS free-boundary equilibria are realistic ITER-scale representations of the four SF types
    Equilibria generated with FreeGS in Section 2; idealized, without coil or error-field effects, and with relaxed snowflake definitions as noted by the authors.
  • ad hoc to paper The label 'snowflake' is used for configurations whose X-point separation sigma exceeds the strict snowflake definition
    Section 2.2 states the term is 'employed in a more relaxed manner with increasing sigma, serving as a convenient label'. This is an admitted redefinition of standard terminology that widens the scope of the claims.

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Cite this review

Pith. "Pith review of SOLPS-ITER Numerical Simulations of ITER-scale Snowflake Divertors: Low-Field-Side SF-/SF+ and High-Field-Side SF-/SF+ Configurations." pith.science (2026). https://pith.science/paper/XXQOAAGA

@misc{pith2026250902455,
  author       = {Pith},
  title        = {Pith review of: SOLPS-ITER Numerical Simulations of ITER-scale Snowflake Divertors: Low-Field-Side SF-/SF+ and High-Field-Side SF-/SF+ Configurations},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/XXQOAAGA}},
  note         = {Machine review of arXiv:2509.02455}
}
read the original abstract

With edge plasma code SOLS-ITER, we study four Snowflake (SF) configurations for an ITER-size tokamak, with toroidal magnetic field BT=5T, major radius R=5m and plasma current Ip=10MA. Our aim is to provide insights on SF divertor design for future devices. In this work, the impacts of magnetic geometry and divertor target geometry in the four types of SF configurations on plasma behavior and power exhaust performance are investigated in detail. Low-recycling regime, high-recycling and detachment in the four types of SF divertors are obtained through an upstream density scan. The secondary X-point positions of SF divertors are systematically varied to examine their impact. For Low-Field-Side (LFS) SF- and High-Field-Side (HFS) SF- divertors the observed power splitting, induced by the secondary X-point, is consistent with experimental observations. The effect of target geometry is studied by comparing the flat target plates with the ITER-like divertor shape. The overall simulation results reveal a notable consequence of the LFS SF- divertor: closed structure of the inner target with high inclined plate can compress recycling neutrals originating from the HFS divertor region into the LFS SOL and PFR regions. This results in considerable volumetric dissipation through strong ionization and recombination, causing the connected outer target region to detach. This feature can be considered in the design of the LFS SF- divertor for future devices. For the LFS and HFS SF+ divertors, the region between the two X-points exhibits strong ionization and recombination sources close to the primary X-point. This feature might be beneficial for the formation of an X-point radiator, but would require further impurity seeding simulation study.

Figures

Figures reproduced from arXiv: 2509.02455 by the authors.

Figure 6
Figure 6. 2D distribution of plasma parameters of the SN and the four SF reference cases at the low upstream density condition : [PITH_FULL_IMAGE:figures/full_fig_p012_6.png] view at source ↗
Figure 16
Figure 16. For LFS SF- cases, as the dxx increases, even more power goes to SOL1 region, the [PITH_FULL_IMAGE:figures/full_fig_p020_16.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

25 extracted references · 25 canonical work pages

  1. [11]

    OT1 and OT2 are the main targets and OT1 is connetd with SOL1

    For LFS SF- divertors as Figure 3 (b), there are one inner target named as IT1 and three outer targets named as OT1, OT2, and OT3. OT1 and OT2 are the main targets and OT1 is connetd with SOL1

    work page

  2. [1]

    NEMO Group, Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

    work page

  3. [2]

    MIT Plasma Science and Fusion Center, Cambridge, MA 02139, USA

    work page

  4. [3]

    Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany

    work page

  5. [4]

    DICI, University of Pisa, lg. L. Lazzarino n.1 Pisa, Italy E-mail: haosheng.wu@polito.it Abstract With edge plasma code SOLS-ITER, we study four Snowflake (SF) configurations for an ITER- size tokamak, with toroidal magnetic field BT~5T, major radius R~5m and plasma current Ip~10MA. Our aim is to provide insights on SF divertor design for future devices. In ...

    work page

  6. [5]

    the EU-DEMO [1], J-DEMO [2] and ARC [3], a significant amount of power will be exhausted into the Scape-OƯ Layer (SOL) region

    Introduction For nuclear fusion reactors, e.g. the EU-DEMO [1], J-DEMO [2] and ARC [3], a significant amount of power will be exhausted into the Scape-OƯ Layer (SOL) region. In steady state, the parallel heat flux at the divertor targets, without any mitigation, can be several hundreds of 𝑀𝑊𝑚ିଶ or even serval 𝐺𝑊𝑚ିଶ [4]. This value far exceeds the current en...

    work page

  7. [6]

    Its relationship with the standard LFS SF- is analogous to the relationship between the Super-X divertor and the conventional SN divertor

    For the LFS SF– topology, when the distance between the primary and secondary X-points is significantly extended, the configuration is referred to as an X-point Target (XPT) divertor [8][9]. Its relationship with the standard LFS SF- is analogous to the relationship between the Super-X divertor and the conventional SN divertor. In recent years, the SF diver...

    work page

  8. [7]

    Reference equilibria The equilibria used in this work are generated using FreeGS [27], which is a free-boundary tokamak equilibrium solver

    Equilibria 2.1. Reference equilibria The equilibria used in this work are generated using FreeGS [27], which is a free-boundary tokamak equilibrium solver. The conventional SN equilibrium and the four types of snowflake equilibria are shown in Figure 1, named SN Reference, LFS SF− Reference, LFS SF+ Reference, HFS SF+ Reference and HFS SF− Reference. They ...

    work page

Show all 25 references
  1. [8]

    The corresponding sizes of the plasma grids for the SN, LFS SF-, LFS SF+, HFS SF+ and HFS SF- reference cases are 120×38, 164×42, 130×34, 148×44 and 160×46 respectively

    Modelling setup The orthogonal high-quality plasma computational grids, together with neutral triangular meshes for the reference equilibria, are shown in Figure 2. The corresponding sizes of the plasma grids for the SN, LFS SF-, LFS SF+, HFS SF+ and HFS SF- reference cases ar...

  2. [9]

    The layer adjacent to the core plasma is referred to as the SOL1 region, while the outer layer is referred to as the SOL2 region

    For SF− divertors as Figure 3(b)(e), the secondary X-point is located in the scrape-oƯ layer (SOL) region of the primary X-point, dividing the SOL into two layers. The layer adjacent to the core plasma is referred to as the SOL1 region, while the outer layer is referred to as ...

  3. [10]

    The region between the primary and secondary X-points is defined as the PFR1 region

    For SF+ divertors as Figure3 (c)(d), the secondary X-point is located in the PFR of the primary X-point, dividing it into four distinct regions. The region between the primary and secondary X-points is defined as the PFR1 region. Among the remaining three regions, starting from...

  4. [12]

    The targets connected with SOL region are named IT1 and OT1 The remaining targets are named IT2 and OT2

    For LFS SF+ and HFS SF+ divertors as Figure 3 (c)(d): there are two inner targets and two outer targets. The targets connected with SOL region are named IT1 and OT1 The remaining targets are named IT2 and OT2

  5. [13]

    IT1 and IT2 are the main targets and IT1 is connetd with SOL1

    For HFS SF- divertors as Figure 3 (e), there are three inner targets named as IT1, IT2 and IT3 and one outer target named as OT1. IT1 and IT2 are the main targets and IT1 is connetd with SOL1. As a starting point, we consider a simplified divertor target geometry in which the t...

  6. [14]

    Simulation results of reference cases In this section, a comparative analysis across the simulation results of the SN and four SF reference cases is carried out. The secondary X-point appearing in the SF divertors makes direct modelling of the divertor detachment particularly ...

  7. [15]

    From the top to the bottom rows are the SN, LFS SF-, LFS SF+, HFS SF+, HFS SF- reference cases

    From left to right columns are electron density ne, electron temperature Te, parallel heat load q∥ and target heat load qsurf. From the top to the bottom rows are the SN, LFS SF-, LFS SF+, HFS SF+, HFS SF- reference cases. For the ne and Te, the OMP profiles are also presented ...

  8. [16]

    From the top to the bottom rows are the SN, LFS SF-, LFS SF+, HFS SF+, HFS SF- reference cases

    From left to right columns are electron density ne, electron temperature Te, parallel heat load q∥ and target heat load qsurf . From the top to the bottom rows are the SN, LFS SF-, LFS SF+, HFS SF+, HFS SF- reference cases. For the ne and Te, the OMP profiles are also presented...

  9. [17]

    This is because, in high upstream density conditions, the divertor targets which are connected to the SOL regions, i.e

    For ne,sep, the SN and four SF reference cases reach similar levels ∼3.0×1019ௗm−3, and the discrepancies observed in Figure 4 disappear. This is because, in high upstream density conditions, the divertor targets which are connected to the SOL regions, i.e. IT1, OT1 and OT2, of...

  10. [18]

    The computational meshes which correspond to the equilibria in section 2.2, together with dxx, σ and θ values, are summarized in Figure 13

    EƯect of magnetic geometry In this section, the eƯect of magnetic geometry on plasma behavior and power exhaust performance in each type of SF divertors are studied by scanning the secondary X-point position as mentioned in section 2.2. The computational meshes which correspon...

  11. [19]

    A closed divertor [41][42] can reflect neutrals in the SOL region; this allows detachment also at low upstream density

    EƯect of target geometry The geometry of the target plate plays a critical role in shaping plasma profiles because it aƯects the neutral recycling dynamics. A closed divertor [41][42] can reflect neutrals in the SOL region; this allows detachment also at low upstream density. Th...

  12. [20]

    In the HFS SF- IL case, the outer separatrix lines do not terminate at the outer IL divertor structure

    The IL target shapes in the four SF configurations are the same but have been horizontally and/or vertically shifted to place the strike points at the same position as those in the reference cases in Section 4, thereby minimizing diƯerences in connection length near the separat...

  13. [21]

    Therefore, the secondary X-point needs to be positioned so as to minimize the distance between IT1 and OT1, bringing the two targets into the closest possible proximity

    Placement of the secondary X-point: The introduction of the secondary X-point splits the SOL into SOL1 and SOL2, eƯectively “bending” LFS SOL1 toward the HFS side. Therefore, the secondary X-point needs to be positioned so as to minimize the distance between IT1 and OT1, bring...

  14. [22]

    As a result, the OT1 target can benefit from this dissipation and more readily achieve detachment

    IT1 target shaping: The shape of the IT1 target should compress recycling neutrals, eƯiciently directing them into the PFR3 and LFS SOL1 regions to enhance volumetric energy dissipation. As a result, the OT1 target can benefit from this dissipation and more readily achieve detachment

  15. [23]

    Inclined target plates: Highly inclined target plates for IT1 and OT2 are recommended, as they can significantly reduce the surface heat flux qsurf through reducing the poloidal tilting angle

  16. [24]

    On the other hand, it should allow the power entering SOL2 to be eƯectively mitigated by the inclined target angle

    Optimization of the distance dxx: On the one hand, dxx should be optimized to fully utilize volumetric dissipation and remove as much power as possible in the SOL1 region. On the other hand, it should allow the power entering SOL2 to be eƯectively mitigated by the inclined tar...

  17. [25]

    Overview of EU DEMO design and R&D activities,

    Summary and Outlook In this paper, ITER-scale snowflake (SF) divertors are numerically studied with the SOLPS-ITER code. Four configuration types are considered including: Low-Field Side SF− (LFS SF−), Low- Field Side SF+ (LFS SF+), High-Field Side SF+ (HFS SF+), and High-Field ...

    2014

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Reviewed August 5, 2026 · model on record in the stance chip above.