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Title: Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

Abstract

The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. Here, this study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λdiv (=[L || ν eiΩi]/c sΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s, but only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with A s for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and A s is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly,more » we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, ID α , does scale with A s where Λdiv does and even where Λdiv does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E × B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Therefore, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.« less

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1];  [2];  [3];  [2];  [4];  [5];  [2];  [6];  [7];  [8];  [9];  [2]; ORCiD logo [2];  [10];  [2]; ORCiD logo [8]
  1. Univ. of York (United Kingdom)
  2. CCFE, Culham Science Centre, Abingdon (United Kingdom)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of York (United Kingdom); Institut für Energie-und Klimaforschung—Plasmaphysik, Julich (Germany). Forschungszentrum Jülich Gmbh
  5. Hungarian Academy of Sciences, Budapest (Hungary)
  6. CCFE, Culham Science Centre, Abingdon (United Kingdom); Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Lisbon (Portugal)
  7. Associazione EURATOM-ENEA sulla Fusione, Frascati, Rome (Italy)
  8. Institut für Energie-und Klimaforschung—Plasmaphysik, Julich (Germany). Forschungszentrum Jülich Gmbh
  9. Association EURATOM-CEA, CEA/DSM/DRFC CEA-Cadarache (France)
  10. Technical Univ. of Denmark, Roskilde (Denmark)
Publication Date:
Research Org.:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
Contributing Org.:
JET Contributors
OSTI Identifier:
1616396
Report Number(s):
LLNL-JRNL-806922
Journal ID: ISSN 0029-5515; 1011269; TRN: US2106444
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., and Wiesen, S. Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas. United States: N. p., 2018. Web. doi:10.1088/1741-4326/aaad78.
Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., & Wiesen, S. Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas. United States. https://doi.org/10.1088/1741-4326/aaad78
Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., and Wiesen, S. 2018. "Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas". United States. https://doi.org/10.1088/1741-4326/aaad78. https://www.osti.gov/servlets/purl/1616396.
@article{osti_1616396,
title = {Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas},
author = {Wynn, A. and Lipschultz, B. and Cziegler, I. and Harrison, J. and Jaervinen, A. and Matthews, G. F. and Schmitz, J. and Tal, B. and Brix, M. and Guillemaut, C. and Frigione, D. and Huber, A. and Joffrin, E. and Kruzei, U. and Militello, F. and Nielsen, A. and Walkden, N. R. and Wiesen, S.},
abstractNote = {The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. Here, this study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λdiv (=[L || ν eiΩi]/c sΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s, but only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with A s for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and A s is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, I–D α , does scale with A s where Λdiv does and even where Λdiv does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E × B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Therefore, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.},
doi = {10.1088/1741-4326/aaad78},
url = {https://www.osti.gov/biblio/1616396}, journal = {Nuclear Fusion},
issn = {0029-5515},
number = 5,
volume = 58,
place = {United States},
year = {Wed Feb 07 00:00:00 EST 2018},
month = {Wed Feb 07 00:00:00 EST 2018}
}

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Works referenced in this record:

Progress at JET in integrating ITER-relevant core and edge plasmas within the constraints of an ITER-like wall
journal, February 2015


Blob birth and transport in the tokamak edge plasma: Analysis of imaging data
journal, September 2006


Experimental investigation of transport phenomena in the scrape-off layer and divertor
journal, February 1997


Plasma–surface interaction, scrape-off layer and divertor physics: implications for ITER
journal, August 2007


An experimental investigation of the high density transition of the scrape-off layer transport in ASDEX Upgrade
journal, November 2014


Flow reversal, convection, and modeling in the DIII-D divertor
journal, December 1998


Upgrade of the lithium beam diagnostic at JET
journal, October 2010


Beryllium migration in JET ITER-like wall plasmas
journal, May 2015


Role of divertor geometry on detachment in ASDEX Upgrade
journal, March 1999


Dynamics and stability of divertor detachment in H-mode plasmas on JET
journal, July 2017


Implications of high density operation on SOL transport: A multimachine investigation
journal, August 2015


Overview of the JET results in support to ITER
journal, June 2017


Effect of Drift Waves on Plasma Blob Dynamics
journal, May 2012


Collisionality and magnetic geometry effects on tokamak edge turbulent transport. I. A two-region model with application to blobs
journal, November 2006


Recent theoretical progress in understanding coherent structures in edge and SOL turbulence
journal, October 2008


The GBS code for tokamak scrape-off layer simulations
journal, June 2016


Development of a mirror-based endoscope for divertor spectroscopy on JET with the new ITER-like wall (invited)
journal, October 2012


Blob dynamics in the TORPEX experiment: a multi-code validation
journal, January 2016


Experimental divertor physics
journal, June 1997


Comments on particle and energy balance in the edge plasma of Alcator C-Mod
journal, September 1998


Transport by intermittent convection in the boundary of the DIII-D tokamak
journal, November 2001


Divertor Physics Research on Alcator C-Mod
journal, April 2007


Characterization of 3D filament dynamics in a MAST SOL flux tube geometry
journal, August 2013


Effects of parallel electron dynamics on plasma blob transport
journal, August 2012


Simulations of edge and scrape off layer turbulence in mega ampere spherical tokamak plasmas
journal, August 2012


Material erosion at the vessel walls of future fusion devices
journal, March 2003


Numerical investigation of isolated filament motion in a realistic tokamak geometry
journal, September 2015


A study on the density shoulder formation in the SOL of H-mode plasmas
journal, August 2017


Effects of divertor geometry on tokamak plasmas
journal, May 2001


Experimental Validation of a Filament Transport Model in Turbulent Magnetized Plasmas
journal, November 2015


Recent progress towards a quantitative description of filamentary SOL transport
journal, April 2017


The Plasma Boundary of Magnetic Fusion Devices
journal, January 2001


Stochastic Modeling of Intermittent Scrape-Off Layer Plasma Fluctuations
journal, June 2012


Cross-field plasma transport and main-chamber recycling in diverted plasmas on Alcator C-Mod
journal, December 2000


JET ITER-like wall—overview and experimental programme
journal, December 2011


Particle and energy transport scalings in the ASDEX scrape-off layer
journal, December 1992


Interchange turbulence in the TCV scrape-off layer
journal, December 2005


Particle transport in the scrape-off layer and its relationship to discharge density limit in Alcator C-Mod
journal, May 2001


Collisionality dependent transport in TCV SOL plasmas
journal, November 2007


On scrape off layer plasma transport
journal, May 2001


Investigation of the origin of neutrals in the main chamber of Alcator C-Mod
journal, May 2002


Scaling of the tokamak near the scrape-off layer H-mode power width and implications for ITER
journal, August 2013


Evidence for electromagnetic fluid drift turbulence controlling the edge plasma state in the Alcator C-Mod tokamak
journal, November 2005


Modeling plasma contact with the main vessel walls of a divertor tokamak
journal, August 2002


First nitrogen-seeding experiments in JET with the ITER-like Wall
journal, July 2013


An analytic model for flow reversal in divertor plasmas
journal, July 1987


Possible influence of near SOL plasma on the H-mode power threshold
journal, August 2017


Comparison of particle transport in the scrape-off layer plasmas of Alcator C-Mod and DIII-D
journal, September 2005


Far SOL transport and main wall plasma interaction in DIII-D
journal, November 2005


Experimental Evidence of Intermittent Convection in the Edge of Magnetic Confinement Devices
journal, July 2001


The magnitude of plasma flux to the main-wall in the DIII-D tokamak
journal, September 2005


Plasma Edge Physics with B2-Eirene
journal, February 2006


Experimental Evidence of Intermittent Convection in the Edge of Magnetic Confinement Devices
text, January 2001


Works referencing / citing this record:

Neutral density estimation in the ASDEX upgrade divertor from deuterium emissivity measurements during detachment and shoulder formation
journal, September 2019


Scrape-off layer transport and filament characteristics in high-density tokamak regimes
journal, October 2019


On the role of filaments in perpendicular heat transport at the scrape-off layer
journal, July 2018