Variation of particle exhaust with changes in divertor magnetic balance

Pétrie, T.W.; Allen, S. L.; Brooks, N.H.; Fenstermacher, M.E.; Ferron, J. R.; Greenfield, C. M.; Groth, M.; Hyatt, A.W.; Mahdavi, M. A.; Porter, G. D.; Rensink, M.E.; Schaffer, M. J.; Wade, M. R.; Watkins, J. G.

doi:10.1088/0029-5515/46/1/007

Cited by 11 publications

(8 citation statements)

References 32 publications

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“…The differences between the two B × ∇B cases suggest that particle flows in the SOL and divertor(s) that depend on the direction of the toroidal field may be in play. For example, previous work in analysing particle pumping data from DIII-D [9] indicated that the poloidal distribution of neutrals between inner and outer divertors (and ultimately the exhaust rates of each divertor cryopump) was strongly influenced by B × ∇B and E × B-induced particle flows in the divertor and SOL. (The electric field driving the E × B flow is largely generated by the radial gradient of the electron temperature with respect to the flux surfaces in the SOL and divertor.)…”

Section: Discussionmentioning

confidence: 99%

“…Previous studies on DIII-D and other tokamaks, however, have indicated that both the direction of the toroidal magnetic field B T and the degree of magnetic balance between divertors (i.e. the degree to which the plasma shape is considered single-null (SN) or double-null (DN)) are important factors in determining recycling behaviour [8] and effectiveness of active particle pumping [9]. In light of these results, it becomes uncertain as to whether the favourable results of the puff-andpump experiment reported in [7] can be extended to cases having different magnetic balance and/or B T direction.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of radiating divertor behaviour in single-null and double-null plasmas in DIII-D

Pétrie¹,

Brooks²,

Fenstermacher³

et al. 2008

Nucl. Fusion

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‘Puff-and-pump’ radiating divertor scenarios, applied to both upper single-null (SN) and double-null (DN) H-mode plasmas, result in a 30–60% increase in radiated power with little or no decrease in τ E . Argon was injected into the private flux region of the upper divertor, and plasma flow into the upper divertor was enhanced by a combination of deuterium gas puffing upstream of the divertor targets and particle pumping at the targets. For the same constant deuterium injection rate, argon penetrated the main plasma of SNs more rapidly and reached a higher steady-state concentration when the B × ∇ B -ion drift direction was towards the divertor (V ∇B↑) rather than away from the divertor (V ∇B↓). We also found that the initial rate at which argon accumulated inside DN plasmas was more than twice that of comparable SN plasmas having the same B × ∇ B -ion drift direction. In DNs, the radiated power was not shared equally between divertors during argon injection. Only when the B × ∇ B ion drift direction was away from the divertor were both significant increases in divertor radiated power and an accumulation of argon in the divertor observed, based on spectroscopic measurements of Ar II. Our data suggest that an unbalanced DN shape where the B × ∇ B -ion drift is directed away from the dominant divertor may provide the best chance of successfully coupling a radiating divertor approach with a higher performance H-mode plasma.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comparison of radiating divertor behaviour in single-null and double-null plasmas in DIII-D

Pétrie¹,

Brooks²,

Fenstermacher³

et al. 2008

Nucl. Fusion

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“…Accurate gas balance measurements in JET, with strike points placed on the vertical tiles above the pumping apertures in the MarkII-GB SRP, have shown that long term retention and hence presumably co-deposition can be reduced to zero when plasma interaction with cold areas is avoided [86]. DIII-D has shown the importance of two factors in determining how effectively the deuterium particle inventory in a tokamak plasma can be controlled through pumping at the divertor target(s): one is the divertor magnetic balance and another is the direction of B × ∇B ion drift with respect to the X-point(s) [88].…”

Section: Recycling/wall Retention and Carbon Migrationmentioning

confidence: 99%

Conference summary: progress in experiments on confinement, plasma–material interactions and innovative confinement concepts

Ninomiya¹

2005

Nucl. Fusion

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This paper summarizes the results presented at the 20th IAEA Fusion Energy Conference 2004 in the sessions on confinement, plasma-material interactions and innovative confinement concepts. The highlights of the presentations are as follows. Long pulse operation has been achieved with high beta and high bootstrap fraction for periods much longer than the current diffusion time. The discharge scenario optimization and its extrapolation towards ITER have progressed remarkably. Significant progress has been made in the understanding of global confinement and transport physics. Progress has also been made in material and retention/migration studies. These results will greatly contribute to ITER and the ultimate goal of fusion power generation.

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“…Research on particle exhaust in DIII‐D DN plasmas with “standard” DIII‐D divertor geometry has shown that the drift direction (set by the toroidal field direction) strongly modifies particle removal by cryopumping . To understand this result, it is useful to introduce the standard picture of asymmetric divertor flows associated with the E × B drift, as sketched in Figure .…”

Section: Introductionmentioning

confidence: 99%

Drift effects and up–down asymmetry in balanced double‐null DIII‐D divertor configurations

Meier

Covele

Guo

et al. 2018

Contributions to Plasma Physics

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In a preliminary design study for a small‐angle slot (SAS) divertor configuration suitable for DIII‐D double‐null advanced tokamak (AT) plasmas, a conceptual “SAS 2” slot divertor configuration has been modelled with SOLPS‐ITER. A balanced double‐null equilibrium, representing an H‐mode AT plasma, is employed, with 5 MW neutral beam input power. In simulations with fully recycling walls and no pumping, an up–down‐symmetric open divertor geometry is compared with the SAS 2 configuration. In density scans without electric or magnetic drifts, the upstream separatrix electron density needed to achieve detachment at both target strike points (ne, sep, det.) is ∼35% lower in SAS 2 than in the open configuration, with ne, sep, det. = 1.66 and 2.59 × 1019 m−3, respectively. With drifts, the same ∼35% difference remains, but detachment density for each configuration is shifted up by ∼15%, giving ne, sep, det. = 1.94 and 2.99 × 1019 m−3, respectively. Cryopumping is modelled for the SAS 2 divertor, and with a pump duct deep in the upper slot on the common‐flux side, detachment density is shifted up by ∼15–20%. Strong pumping in the upper slot delays detachment there compared with the lower slot, regardless of drift direction. This research sets the stage for future modelling that would explore more sophisticated cryopumping configurations, and sensitivity of divertor performance to changes in magnetic balance and input power.

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Variation of particle exhaust with changes in divertor magnetic balance

Cited by 11 publications

References 32 publications

Comparison of radiating divertor behaviour in single-null and double-null plasmas in DIII-D

Comparison of radiating divertor behaviour in single-null and double-null plasmas in DIII-D

Conference summary: progress in experiments on confinement, plasma–material interactions and innovative confinement concepts

Drift effects and up–down asymmetry in balanced double‐null DIII‐D divertor configurations

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