skip to main content


This content will become publicly available on April 19, 2019

Title: Helical variation of density profiles and fluctuations in the tokamak pedestal with applied 3D fields and implications for confinement

Small 3D perturbations to the magnetic field in DIII-D ( δ B / B ~ 2 × 10 - 4 ) result in large modulations of density fluctuation amplitudes in the pedestal, which are shown using Doppler backscattering measurements to vary by a factor of 2. Helical perturbations of equilibrium density within flux surfaces have previously been observed in the pedestal of DIII-D plasmas when 3D fields are applied and were correlated with density fluctuation asymmetries in the pedestal. These intra-surface density and pressure variations are shown through two fluid MHD modeling studies using the M3D-C1 code to be due to the misalignment of the density and temperature equilibrium iso-surfaces in the pedestal region. This modeling demonstrates that the phase shift between the two iso-surfaces corresponds to the diamagnetic direction of the two species, with the mass density surfaces shifted in the ion diamagnetic direction relative to the temperature and magnetic flux iso-surfaces. Finally, the resulting pedestal density, potential, and turbulence asymmetries within flux surfaces near the separatrix may be at least partially responsible for several poorly understood phenomena that occur with the application of 3D fields in tokamaks, including density pump out and the increase in power required to transition from L- to H-mode.
ORCiD logo [1] ;  [2] ;  [1] ; ORCiD logo [3] ; ORCiD logo [4] ; ORCiD logo [5] ;  [6] ; ORCiD logo [5] ;  [1] ;  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. General Atomics, San Diego, CA (United States)
  6. Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
Publication Date:
Grant/Contract Number:
AC05-00OR22725; AC02-09CH11466; FG02-99ER54527; FG02-08ER54984; FG02-08ER54999; FC02-04ER54698
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 5; Journal ID: ISSN 1070-664X
American Institute of Physics (AIP)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Univ. of California, Los Angeles, CA (United States); Univ. of Wisconsin, Madison, WI (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma flows; turbulent flows; plasma confinement; tokamaks; hydrodynamics; thermodynamic processes; computer science and technology; deformation; turbulence simulations; diamagnetism
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1433757; OSTI ID: 1437165