Taming the plasma–material interface with the ‘snowflake’ divertor in NSTX

Soukhanovskii, V.; Ahn, J.-W.; Bell, R. E.; Gates, D.; Gerhardt, S.; Kaita, R.; Kolemen, Egemen; LeBlanc, B.; Maingi, R.; Makowski, M. A.; Maqueda, R. J.; McLean, A.G.; Ménard, J.; Mueller, D.; Paul, S. F.; Raman, R.; Roquemore, A. L.; Ryutov, D. D.; Sabbagh, S. A.; Scott, H. A.

doi:10.1088/0029-5515/51/1/012001

Cited by 79 publications

(74 citation statements)

References 29 publications

(54 reference statements)

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“…In particular, a third divertor PF coil (PF1C) will be added to the CS as shown in Figure 15b to support the snowflake and to improve flux expansion and strike-point control generally. Recently, the snowflake divertor has demonstrated large (factor of 3) reductions in peak heat flux as shown in Figure 16, and also up to a 50% reduction in carbon impurity production [12]. Thus, the snowflake divertor projects favorably to mitigating high divertor heat fluxes projected for NSTX Upgrade and in particular for enabling flat-top durations up to 5s at 2MA.…”

Section: Divertor Power Handlingmentioning

confidence: 99%

Overview of the physics and engineering design of NSTX upgrade

et al. 2012

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Abstract-The spherical tokamak (ST) is a leading candidate for a fusion nuclear science facility (FNSF) due to its compact size and modular configuration. The National Spherical Torus eXperiment (NSTX) is a MA-class ST facility in the U.S. actively developing the physics basis for an ST-based FNSF. In plasma transport research, ST experiments exhibit a strong (nearly inverse) scaling of normalized confinement with collisionality, and if this trend holds at low collisionality, high fusion neutron fluences could be achievable in very compact ST devices. A major motivation for the NSTX Upgrade (NSTX-U) is to span the next factor of 3-6 reduction in collisionality. To achieve this collisionality reduction with equilibrated profiles, NSTX-U will double the toroidal field, plasma current, and NBI heating power and increase the pulse length from 1-1.5s to 5s. In the area of stability and advanced scenarios, plasmas with higher aspect ratio and elongation, high βN , and broad current profiles approaching those of an ST-based FNSF have been produced in NSTX using active control of the plasma β and advanced resistive wall mode control. High non-inductive current fractions of 70% have been sustained for many current diffusion times, and the more tangential injection of the 2nd NBI of the Upgrade is projected to increase the NBI current drive by up to a factor of 2 and support 100% non-inductive operation. More tangential NBI injection is also projected to provide non-solenoidal current ramp-up (from IP = 0.4MA up to 0.8-1MA) as needed for an ST-based FNSF. In boundary physics, NSTX and higher-A tokamaks measure an inverse relationship between the scrape-off layer heat-flux width and plasma current that could unfavorably impact nextstep devices. Recently, NSTX has successfully demonstrated very high flux expansion and substantial heat-flux reduction using a snowflake divertor configuration, and this type of divertor is incorporated in the NSTX-U design. The physics and engineering design supporting NSTX Upgrade are described.

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Section: Divertor Power Handlingmentioning

confidence: 99%

Overview of the physics and engineering design of NSTX upgrade

et al. 2012

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“…8). 31 Another innovative divertor configuration that can lead to high flux expansion, the super-X divertor (SXD) configuration, is planned on MAST-U. Utilization of lithium as an alternative plasma facing material has been also actively pursued.…”

Section: A Overviewmentioning

confidence: 99%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ∼ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ∼ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

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“…Accomplishing these divertor solutions, and studying their compatibility with the high-performance plasma core, will be a major part of the research program. Candidate solutions under consideration include partial detachment [147,148] or snowflake divertors [45,149]. Table A2: TRANSP runs and basic parameters corresponding to the data in table #3 Table A3: TRANSP runs and basic parameters corresponding to the data in table #4 Table A4: TRANSP runs and basic parameters corresponding to the data in table #5 Table A5: TRANSP runs and basic parameters corresponding to the data in table #6 …”

Section: : Summary and Discussionmentioning

confidence: 99%

Exploration of the Equilibrium Operating Space For NSTX-Upgrade

Gerhardt¹

2012

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Taming the plasma–material interface with the ‘snowflake’ divertor in NSTX

Cited by 79 publications

References 29 publications

Overview of the physics and engineering design of NSTX upgrade

Overview of the physics and engineering design of NSTX upgrade

Recent progress on spherical torus research

Exploration of the Equilibrium Operating Space For NSTX-Upgrade

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