Investigation of dust shielding effect of intrinsic ergodic magnetic field line structures in the peripheral plasma in the large helical device

Recent long pulse discharges in the large helical device (LHD) have been interrupted by radiation collapse induced by the emission of dust from the surface of the vacuum vessel and the divertor region. The dust shielding effect by intrinsic ergodic magnetic field line structures (ergodic layer) formed around the main plasma confinement region is investigated using a three‐dimensional peripheral plasma fluid code (EMC3‐EIRENE) coupled with a dust transport simulation code (DUSTT). Simulations performed in three different magnetic configurations with narrow, medium, and wide ergodic layers show that the wide ergodic layer is not always effective in shielding the main plasma from the dust emission. Optimum operational regimes for controlling the influence of the dust emission on the sustainment of plasma discharges are found by investigating the impurity ion content in the peripheral plasma for various plasma heating powers and plasma densities in the three magnetic configurations.

[1]  M. Shoji,et al.  Simulation of impurity transport in the peripheral plasma due to the emission of dust in long pulse discharges on the Large Helical Device , 2017 .

[2]  M. Shoji,et al.  Simulation Analysis of Carbon Deposition Profile in the Closed Helical Divertor Configuration in the Large Helical Device , 2016 .

[3]  T. Mutoh,et al.  Observation of Termination Process of Long Pulse Plasma Discharges Using Stereoscopic Fast Framing Cameras in the Large Helical Device , 2016 .

[4]  H. Yamada,et al.  Progress of long pulse discharges by ECH in LHD , 2016 .

[5]  M. Shoji,et al.  Plasma wall interaction in long-pulse helium discharge in LHD - Microscopic modification of the wall surface and its impact on particle balance and impurity generation , 2015 .

[6]  M. Shoji,et al.  Studies of dust transport in long pulse plasma discharges in the large helical device , 2015 .

[7]  M. Shoji,et al.  First EMC3‐EIRENE Simulations with Divertor Legs of LHD in Realistic Device Geometry , 2014 .

[8]  H. Takenaga,et al.  Simulation of dynamics of carbon dust particles in the JT-60U tokamak , 2011 .

[9]  Takashi Shimozuma,et al.  Goal and Achievements of Large Helical Device Project , 2010 .

[10]  A. Sagara,et al.  Characterization of Dust Particles Ranging in Size from 1 nm to 10 µm Collected in the LHD , 2009 .

[11]  H. Yamada,et al.  Modelling of Impurity Transport in Ergodic Layer of LHD , 2008 .

[12]  T. Rognlien,et al.  Transport of dust particles in tokamak devices , 2007 .

[13]  S. Krasheninnikov,et al.  Modelling of dynamics and transport of carbon dust particles in tokamaks , 2007 .

[14]  D. Reiter,et al.  Transport in island divertors: physics, 3D modelling and comparison to first experiments on W7-AS* , 2002 .

[15]  Masaki Osakabe,et al.  Multifaceted asymmetric radiation from the edge-like asymmetric radiative collapse of density limited plasmas in the Large Helical Device , 2001 .

[16]  A. Sagara,et al.  The large helical device (LHD) helical divertor , 1994 .