Divertor leg filaments in NSTX-U

Scotti, Filippo; Zweben, Stewart; Soukhanovskii, Vlad; Baver, Derek; Myra, James

doi:10.1088/1741-4326/aae49f

Divertor leg filaments in NSTX-U

Journal Article · Wed Oct 24 00:00:00 EDT 2018 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aae49f· OSTI ID:1485055

Scotti, Filippo ^[1]; Zweben, Stewart ^[2]; ^[1]; Baver, Derek ^[3]; ^[3]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Lodestar Research Corp., Boulder, CO (United States)

This study presents the first observation of divertor localized turbulence in the NSTX-Upgrade spherical tokamak. Previous work in NSTX discharges described fluctuations on the divertor target due to blobs generated on the low field side midplane. In the region that shows disconnection from upstream turbulence (private flux region and proximity of the strike point), divertor-localized fluctuations are observed via imaging of C III and D-α emission in diverted L-mode discharges and are characterized in this paper. Field-aligned filaments connected to the divertor target plate are radially localized at the separatrix on the outer divertor leg and in the private flux region on the inner divertor leg. These are limited to the region below the X-point with fluctuation levels up to 10%–20%. The filaments have comparable poloidal and radial correlation lengths (10–100 ion gyroradii ρ_i) and parallel correlation lengths of several meters. Toroidal mode numbers are in the range of 10–30 and 2–10 for outer and inner leg filaments. The poloidal motion of outer leg filaments has the same direction and comparable magnitude to advection due to E x B drift calculated by the multi-fluid edge transport code UEDGE with inclusion of cross field drifts. Disconnection between inner and outer leg filaments as well as the absence of correlation with upstream turbulence support the hypothesis of X-point disconnection for divertor leg filaments. Simulations with the ArbiTER linear eigenvalue solver and a resistive-balooning model were performed with a simulation grid limited to the divertor legs. Instabilities localized to the bad curvature side of the divertor legs were observed, in qualitative agreement with the experiment.

View Accepted Manuscript (DOE)

Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE; USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: AC02-09CH11466; AC52-07NA27344; FG02-02ER54678

OSTI ID:: 1485055

Alternate ID(s):: OSTI ID: 1513111
OSTI ID: 22929568

Report Number(s):: LLNL-JRNL--744120

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 12 Vol. 58; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

References (34)

Instability Driven by Sheath Boundary Conditions and Limited to Divertor Legs Ryutov, D. D.; Cohen, R. H. Contributions to Plasma Physics, Vol. 44, Issue 13 https://doi.org/10.1002/ctpp.200410023	journal	April 2004
Phenomenology of Flute-Like Perturbations in the Divertor Region Cohen, R. H.; Ryutov, D. D. Contributions to Plasma Physics, Vol. 36, Issue 2-3 https://doi.org/10.1002/ctpp.2150360212	journal	January 1996
A fully implicit, time dependent 2-D fluid code for modeling tokamak edge plasmas Rognlien, T. D.; Milovich, J. L.; Rensink, M. E. Journal of Nuclear Materials, Vol. 196-198 https://doi.org/10.1016/S0022-3115(06)80058-9	journal	December 1992
Spatial structure of scrape-off-layer filaments near the midplane and X-point regions of Alcator-C-Mod Terry, J. L.; Zweben, S. J.; Umansky, M. V. Journal of Nuclear Materials, Vol. 390-391 https://doi.org/10.1016/j.jnucmat.2009.01.152	journal	June 2009
Fast imaging of filaments in the X-point region of Alcator C-Mod Terry, J. L.; Ballinger, S.; Brunner, D. Nuclear Materials and Energy, Vol. 12 https://doi.org/10.1016/j.nme.2016.11.020	journal	August 2017
The poloidal distribution of turbulent fluctuations in the Mega-Ampère Spherical Tokamak Antar, G. Y.; Counsell, G.; Ahn, J. -W. Physics of Plasmas, Vol. 12, Issue 3 https://doi.org/10.1063/1.1861894	journal	March 2005
Collisionality and magnetic geometry effects on tokamak edge turbulent transport. I. A two-region model with application to blobs Myra, J. R.; Russell, D. A.; D’Ippolito, D. A. Physics of Plasmas, Vol. 13, Issue 11 https://doi.org/10.1063/1.2364858	journal	November 2006
Strongly intermittent edge plasma transport: Issues with modeling and interpretation of experimental data Krasheninnikov, S. I.; Pigarov, A. Yu.; Soboleva, T. K. Physics of Plasmas, Vol. 16, Issue 1 https://doi.org/10.1063/1.3050076	journal	January 2009
Plasma transport and turbulence in the Helimak: Simulation and experiment Li, B.; Rogers, B. N.; Ricci, P. Physics of Plasmas, Vol. 16, Issue 8 https://doi.org/10.1063/1.3212591	journal	August 2009
Convective transport by intermittent blob-filaments: Comparison of theory and experiment D’Ippolito, D. A.; Myra, J. R.; Zweben, S. J. Physics of Plasmas, Vol. 18, Issue 6 https://doi.org/10.1063/1.3594609	journal	June 2011
Time-dependent 2-D modeling of edge plasma transport with high intermittency due to blobs Pigarov, A. Yu.; Krasheninnikov, S. I.; Rognlien, T. D. Physics of Plasmas, Vol. 19, Issue 7 https://doi.org/10.1063/1.4739464	journal	July 2012
Full toroidal imaging of non-axisymmetric plasma material interaction in the National Spherical Torus Experiment divertor Scotti, Filippo; Roquemore, A. L.; Soukhanovskii, V. A. Review of Scientific Instruments, Vol. 83, Issue 10 https://doi.org/10.1063/1.4739510	journal	October 2012
The appearance and propagation of filaments in the private flux region in Mega Amp Spherical Tokamak Harrison, J. R.; Fishpool, G. M.; Thornton, A. J. Physics of Plasmas, Vol. 22, Issue 9 https://doi.org/10.1063/1.4929924	journal	September 2015
Theory based scaling of edge turbulence and implications for the scrape-off layer width Myra, J. R.; Russell, D. A.; Zweben, S. J. Physics of Plasmas, Vol. 23, Issue 11 https://doi.org/10.1063/1.4966564	journal	November 2016
Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices Zweben, S. J.; Terry, J. L.; Stotler, D. P. Review of Scientific Instruments, Vol. 88, Issue 4 https://doi.org/10.1063/1.4981873	journal	April 2017
Temperature‐gradient instability induced by conducting end walls Berk, H. L.; Ryutov, D. D.; Tsidulko, Yu. A. Physics of Fluids B: Plasma Physics, Vol. 3, Issue 6 https://doi.org/10.1063/1.859699	journal	June 1991
The two-dimensional structure of radiative divertor plasmas in the DIII-D tokamak Fenstermacher, M. E.; Allen, S. L.; Brooks, N. H. Physics of Plasmas, Vol. 4, Issue 5 https://doi.org/10.1063/1.872278	journal	May 1997
Electron temperature gradient induced instability in tokamak scrape-off layers Berk, H. -L; Cohen, R. H.; Ryutov, D. D. Nuclear Fusion, Vol. 33, Issue 2 https://doi.org/10.1088/0029-5515/33/2/I07	journal	February 1993
Effect of the magnetic field geometry on the flute-like perturbations near the divertor X point Farina, D.; Pozzoli, R.; Ryutov, D. D. Nuclear Fusion, Vol. 33, Issue 9 https://doi.org/10.1088/0029-5515/33/9/I06	journal	September 1993
High-speed imaging of edge turbulence in NSTX Zweben, S. J.; Maqueda, R. J.; Stotler, D. P. Nuclear Fusion, Vol. 44, Issue 1 https://doi.org/10.1088/0029-5515/44/1/016	journal	December 2003
Theory and fluid simulations of boundary-plasma fluctuations Cohen, R. H.; LaBombard, B.; Ryutov, D. D. Nuclear Fusion, Vol. 47, Issue 7 https://doi.org/10.1088/0029-5515/47/7/012	journal	June 2007
Intermittent divertor filaments in the National Spherical Torus Experiment and their relation to midplane blobs Maqueda, R. J.; Stotler, D. P. Nuclear Fusion, Vol. 50, Issue 7 https://doi.org/10.1088/0029-5515/50/7/075002	journal	June 2010
Heuristic drift-based model of the power scrape-off width in low-gas-puff H-mode tokamaks Goldston, R. J. Nuclear Fusion, Vol. 52, Issue 1 https://doi.org/10.1088/0029-5515/52/1/013009	journal	December 2011
Overview of the physics and engineering design of NSTX upgrade Menard, J. E.; Gerhardt, S.; Bell, M. Nuclear Fusion, Vol. 52, Issue 8 https://doi.org/10.1088/0029-5515/52/8/083015	journal	July 2012
Scaling of the tokamak near the scrape-off layer H-mode power width and implications for ITER Eich, T.; Leonard, A. W.; Pitts, R. A. Nuclear Fusion, Vol. 53, Issue 9 https://doi.org/10.1088/0029-5515/53/9/093031	journal	August 2013
Experimental investigation of the parallel structure of fluctuations in the scrape-off layer of Alcator C-Mod Grulke, O.; Terry, J. L.; Cziegler, I. Nuclear Fusion, Vol. 54, Issue 4 https://doi.org/10.1088/0029-5515/54/4/043012	journal	March 2014
On the possibility of the sheath-driven, finite-beta modes localized near the divertor plate Cohen, R. H.; Ryutov, D. D. Plasma Physics and Controlled Fusion, Vol. 47, Issue 8 https://doi.org/10.1088/0741-3335/47/8/004	journal	July 2005
Overview of NSTX Upgrade initial results and modelling highlights Menard, J. E.; Allain, J. P.; Battaglia, D. J. Nuclear Fusion, Vol. 57, Issue 10, Article No. 102006 https://doi.org/10.1088/1741-4326/aa600a	journal	June 2017
Gyrokinetic projection of the divertor heat-flux width from present tokamaks to ITER Chang, C. S.; Ku, S.; Loarte, A. Nuclear Fusion, Vol. 57, Issue 11 https://doi.org/10.1088/1741-4326/aa7efb	journal	August 2017
Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U Boyer, M. D.; Battaglia, D. J.; Mueller, D. Nuclear Fusion, Vol. 58, Issue 3 https://doi.org/10.1088/1741-4326/aaa4d0	journal	January 2018
Scenario development during commissioning operations on the National Spherical Torus Experiment Upgrade Battaglia, D. J.; Boyer, M. D.; Gerhardt, S. Nuclear Fusion, Vol. 58, Issue 4 https://doi.org/10.1088/1741-4326/aaa6e0	journal	February 2018
Experimental Observation of the Blob-Generation Mechanism from Interchange Waves in a Plasma Furno, I.; Labit, B.; Podestà, M. Physical Review Letters, Vol. 100, Issue 5 https://doi.org/10.1103/PhysRevLett.100.055004	journal	February 2008
Eigenvalue Solver for Fluid and Kinetic Plasma Models in Arbitrary Magnetic Topology Baver, D. A.; Myra, J. R.; Umansky, M. V. Communications in Computational Physics, Vol. 20, Issue 1 https://doi.org/10.4208/cicp.191214.021015a	journal	June 2016
Gyrokinetic projection of the divertor heat-flux width from present tokamaks to ITER Chang, C. S.; Ku, S.; Loarte, A. arXiv https://doi.org/10.48550/arxiv.1701.05507	text	January 2017

Cited By (9)

Penetration of filamentary structures into the divertor region of spherical tokamaks Baver, D. A.; Myra, J. R. Physics of Plasmas, Vol. 26, Issue 2 https://doi.org/10.1063/1.5065390	journal	February 2019
On the interplay between MHD instabilities and turbulent transport in magnetically confined plasmas Ida, K. Plasma Physics and Controlled Fusion, Vol. 62, Issue 1 https://doi.org/10.1088/1361-6587/ab4827	journal	October 2019
NSTX/NSTX-U theory, modeling and analysis results Kaye, S. M.; Battaglia, D. J.; Baver, D. Nuclear Fusion, Vol. 59, Issue 11 https://doi.org/10.1088/1741-4326/ab023a	journal	June 2019
3D structure and dynamics of filaments in turbulence simulations of WEST diverted plasmas Nespoli, F.; Tamain, P.; Fedorczak, N. Nuclear Fusion, Vol. 59, Issue 9 https://doi.org/10.1088/1741-4326/ab2813	journal	July 2019
Summary of the 27th IAEA Fusion Energy Conference in the categories of EX/W, EX/D, and ICC Ida, K. Nuclear Fusion, Vol. 59, Issue 11 https://doi.org/10.1088/1741-4326/ab3811	journal	September 2019
Performance assessment of long-legged tightly-baffled divertor geometries in the ARC reactor concept Wigram, M. R. K.; LaBombard, B.; Umansky, M. V. Nuclear Fusion, Vol. 59, Issue 10 https://doi.org/10.1088/1741-4326/ab394f	journal	September 2019
Study of passively stable, fully detached divertor plasma regimes attained in innovative long-legged divertor configurations Umansky, M. V.; LaBombard, B.; Brunner, D. Nuclear Fusion, Vol. 60, Issue 1 https://doi.org/10.1088/1741-4326/ab46f4	journal	October 2019
Disconnection of scrape off layer turbulence between the outer midplane and divertor target plate in NSTX Scotti, F.; Zweben, S.; Myra, J. Nuclear Fusion, Vol. 60, Issue 2 https://doi.org/10.1088/1741-4326/ab5886	journal	December 2019
Penetration Of Filamentary Structures Into The Divertor Region Of Spherical Tokamaks Baver, Derek A.; Myra, James R. Zenodo https://doi.org/10.5281/zenodo.1453440	text	January 2018