Gyrokinetic Simulations of ETG and ITG Turbulence

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Published gyrokinetic continuum-code simulations indicated levels of the electron thermal conductivity {chi}{sub e} due to electron-temperature-gradient (ETG) turbulence large enough to be significant in some tokamaks, while subsequent global particle-in-cell (PIC) simulations gave significantly lower values. We have carried out an investigation of this discrepancy. We have reproduced the key features of the aforementioned PIC simulations using the flux-tube gyrokinetic PIC code, PG3EQ, thereby eliminating global effects and as the cause of the discrepancy. We show that the late-time low-transport state in both of these sets of PIC simulations is a result of discrete particle noise, which is a numerical ... continued below

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Dimits, A.; Nevins, W.; Shumaker, D.; Hammett, G.; Dannert, T.; Jenko, F. et al. October 3, 2006.

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Published gyrokinetic continuum-code simulations indicated levels of the electron thermal conductivity {chi}{sub e} due to electron-temperature-gradient (ETG) turbulence large enough to be significant in some tokamaks, while subsequent global particle-in-cell (PIC) simulations gave significantly lower values. We have carried out an investigation of this discrepancy. We have reproduced the key features of the aforementioned PIC simulations using the flux-tube gyrokinetic PIC code, PG3EQ, thereby eliminating global effects and as the cause of the discrepancy. We show that the late-time low-transport state in both of these sets of PIC simulations is a result of discrete particle noise, which is a numerical artifact. Thus, the low value of {chi}{sub e} along with conclusions about anomalous transport drawn from these particular PIC simulations are unjustified. In our attempts to benchmark PIC and continuum codes for ETG turbulence at the plasma parameters used above, both produce very large intermittent transport. We have therefore undertaken benchmarks at an alternate reference point, magnetic shear s=0.1 instead of s=0.796, and have found that PIC and continuum codes reproduce the same transport levels. Scans in the magnetic shear show an abrupt transition to a high-{chi}{sub e} state as the shear is increased above s=0.4. When nonadiabatic ions are used, this abrupt transition is absent, and {chi}{sub e} increases gradually reaching values consistent with transport analyses of DIII-D, JET, and JT60-U discharges. New results on the balances of zonal-flow driving and damping terms in late-time quasi-steady ITG turbulence and on real-geometry gyrokinetic simulations of shaped DIII-D discharges are also reported.

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PDF-file: 10 pages; size: 0.7 Mbytes

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  • Presented at: 21st IAEA Fusion Energy Conference, Chengdu, China, Oct 16 - Oct 21, 2006

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  • Report No.: UCRL-PROC-225033
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 897932
  • Archival Resource Key: ark:/67531/metadc886017

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  • October 3, 2006

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  • Sept. 22, 2016, 2:13 a.m.

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  • Dec. 7, 2016, 3:09 p.m.

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Dimits, A.; Nevins, W.; Shumaker, D.; Hammett, G.; Dannert, T.; Jenko, F. et al. Gyrokinetic Simulations of ETG and ITG Turbulence, article, October 3, 2006; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc886017/: accessed August 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.