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Title: Comparative H-mode density limit studies in JET and AUG

Journal Article · · Nuclear Materials and Energy
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  1. Culham Science Centre, Abingdon (United Kingdom); Forschungszentrum Juelich (Germany)
  2. Max Planck Society, Garching (Germany). Max Planck Institute for Plasma Physics
  3. Forschungszentrum Juelich (Germany)
  4. Inst. of Superior Tecnico (IST), Lisbon (Portugal)
  5. Culham Science Centre, Abingdon (United Kingdom)
  6. Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Rome (Italy)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  8. Aalto Univ., Otaniemi (Finland)
  9. Ecole Royale Militaire (ERM), Brussels (Belgium). Lab. for Plasma Physics
  10. Alternative Energies and Atomic Energy Commission (CEA), St. Paul lez Durance (France)
+ Show Author Affiliations

Identification of the mechanisms for the H-mode density limit in machines with fully metallic walls, and their scaling to future devices is essential to find for these machines the optimal operational boundaries with the highest attainable density and confinement. Systematic investigations of H-mode density limit plasmas in experiments with deuterium external gas fuelling have been performed on machines with fully metallic walls, JET and AUG and results have been compared with one another. Basically, the operation phases are identical for both tokamaks: the stable H-mode phase, degrading H-mode phase, breakdown of the H-mode with energy confinement deterioration usually accompanied by a dithering cycling phase, followed by the l-mode phase. The observed H-mode density limit on both machines is found close to the Greenwald limit (n/nGW = 0.8–1.1 in the observed magnetic configurations). The similar behavior of the radiation on both tokamaks demonstrates that the density limit (DL) is neither related to additional energy losses from the confined region by radiation, nor to an inward collapse of the hot discharge core induced by overcooling of the plasma periphery by radiation. It was observed on both machines that detachment, as well as the X-point MARFE itself, does not trigger a transition in the confinement regime and thus does not present a limit on the plasma density. It is the plasma confinement, most likely determined by edge parameters, which is ultimately responsible for the transition from H- to l-mode. The measured Greenwald fractions are found to be consistent with the predictions from different theoretical models, based on MHD instability theory in the near-SOL.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE; European Research Council (ERC)
Grant/Contract Number:
AC05-00OR22725; 633053
OSTI ID:
1817580
Journal Information:
Nuclear Materials and Energy, Vol. 12; ISSN 2352-1791
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

References (21)

Deuterium Balmer/Stark spectroscopy and impurity profiles: First results from mirror-link divertor spectroscopy system on the JET ITER-like wall journal July 2013
Recent H-mode density limit studies at JET journal May 2004
The H-mode density limit in the full tungsten ASDEX Upgrade tokamak journal November 2014
A Scrape-off Layer Based Density Limit for JET ELMy H-modes journal January 1998
Theoretical aspects and practical implications of the heuristic drift SOL model journal August 2015
A scrape-off layer based model for Hugill-Greenwald type density limits journal April 1997
Impact of the ITER-like wall on divertor detachment and on the density limit in the JET tokamak journal July 2013
Interpretation of density limits and the H-mode operational diagram through similarity parameters for edge transport mechanisms journal January 1999
Residual carbon content in the initial ITER-Like Wall experiments at JET journal July 2013
Inferring divertor plasma properties from hydrogen Balmer and Paschen series spectroscopy in JET-ILW journal November 2015
A new look at density limits in tokamaks journal December 1988
Upgrade of the lithium beam diagnostic at JET journal October 2010
Recent improvements of the JET lithium beam diagnostic journal October 2012
Dynamic behavior of the L - H transition journal January 1994
High density operation close to Greenwald limit and H mode limit in ASDEX upgrade journal November 1997
L–H power threshold studies in JET with Be/W and C wall journal January 2014
On the physics guidelines for a tokamak DEMO journal June 2013
Electron cyclotron emission radiometer upgrade on the Joint European Torus (JET) tokamak journal October 2004
High resolution Thomson scattering for Joint European Torus (JET) journal October 2004
Integrated predictive modeling of high-mode tokamak plasmas using a combination of core and pedestal models journal November 2003
Heuristic drift-based model of the power scrape-off width in low-gas-puff H-mode tokamaks journal December 2011

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Related Subjects

36 MATERIALS SCIENCE
Density limit
H-mode
Detachment
Greenwald fraction
JET
ASDEX Upgrade