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Title: Understanding ECH density pump-out in DIII-D H-mode plasmas

Here, we show that the often observed ”density pump-out” with Electron Cyclotron Heating (ECH) [C. Angioni et al. [1, 2]], at low density and/or collisionality is the result of an increase in turbulence drive at the plasma edge [1,3,4]. Prior results were limited to comparison of steady-state conditions, before and after the ECH was applied, and thus failed to capture the dynamics of the density pump-out. In this paper, we find, similar to prior results, that when the plasma reaches a new equilibrium after ECH is applied, gyro-kinetic simulations indicate that the plasma has transitioned from the Ion Temperature Gradient (ITG) to a Trapped Electron Mode (TEM) regime around mid-radius. But, this transition from ITG to TEM only occures in the core after 100 ms. The pump-out on the other hand, starts immediately and is strongest around ρ ~ 0.8. Linear gyrokinetic simulations with TGLF show that there is an increase in turbulence drive simultaneously with the density pompous and the Doppler BackScattering (DBS) measures an instant increase in density fluctuations at the same radial location. On the other hand, around mid-radius the DBS measures no increase in density fluctuations. All these calculations along with experimental measurements show that themore » density pump-out is not the result of a change in turbulence type (i.e. not caused by a change from ITG to TEM), but the result of a change in turbulence drive (an increase in linear growth rates), which is later followed by the ITG to TEM transition. We highlight the need for studying not just the equilibrium conditions after a transition, but also the time-dependent changes.« less
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [4] ;  [5] ;  [6] ;  [6] ;  [6]
  1. College of William and Mary, Williamsburg, VA (United States). Dept. of Physics
  2. College of William and Mary, Williamsburg, VA (United States). Dept. of Applied Science
  3. Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
  4. Univ. of Wisconsin, Madison, WI (United States)
  5. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies
  6. General Atomics, San Diego, CA (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; SC0007880; FG03-97ER54415; FG02-08ER54984
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 11; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
OSTI Identifier: