Electron gyroradius scale turbulence is important in the plasma core and in the pedestal, where it can account for 30% of the electron heat loss. Direct multiscale simulations show that electron scale turbulence has an unexpectedly large impact on ion gyroradius scales, but these simulations require tens of millions of CPU core-hours. In the Partnership for Multiscale Gyrokinetic Turbulence, in collaboration with our FASTMath partners, we have developed and implemented higher order methods to periodically sub-cycle electron scale simulations with adaptivity. We have formulated and implemented a first-of-kind reduced toroidal multiscale gyrofluid model, retaining full FLR effects via Bessel functions, using a modified field equation with appropriate electron response at ion and electron scales. The 2D MuSHrooM code closely matches GENE gyrokinetic 2D single scale toroidal linear and nonlinear ITG simulations over a wide range of temperature gradients. Using the reduced model, multi-scale toroidal ITG/ETG simulations have been completed in 50 to 100 times less CPU time than 3D gyrokinetic simulations, i.e, with resources characteristic of single scale 3D ITG gyrokinetic turbulence simulations. Successful multiscale algorithms will be implemented in the GENE code.
The team working on this project includes collaborators outside the PSFC, as listed below.
Manaure Francisquez (PPPL)
Dan Reynolds (SMU, FASTMath)
Cody Balos (LLNL, FASTMath)
Carol Woodward (LLNL, FASTMath)
Ian Gill (Yale University)
Manaure Francisquez (PPPL)
Dan Reynolds (SMU, FASTMath)
Cody Balos (LLNL, FASTMath)
Carol Woodward (LLNL, FASTMath)
Ian Gill (Yale University)
To predict energy transport in future machines, a more practical, yet accurate method is required to account for cross-scale interactions between ion gyroradius and electron gyroradius scales. Our new multiscale algorithms and reduced model will provide first-principles calculations of these effects with computational resources comparable to those for ion scales only.
M. Francisquez, D. R. Ernst, D. Reynolds and C. Balos, “A 2D gyrofluid model for multiscale turbulence and its comparison to gyrokinetics,” 63rd Annual Meeting of the APS Division of Plasma Physics, November 8-12, 2021.
D. R. Ernst, M. Francisquez, D. Reynolds, C. Balos and C. Woodward, “Reduced model and algorithmic test-bed for cross-scale interactions in multi-scale ITG/ETG turbulence,” 2022 International Sherwood Fusion Theory Conference, Santa Rosa, April 4-6, 2022.
caption for figure: (top) Linear growth rate from the MuSHrooM code, evolving our new reduced multiscale gyrofluid model, showing toroidal ITG and ETG modes are included. (bottom) A nonlinear multiscale simulation of coupled toroidal ITG and ETG turbulence in MuSHrooM, using mass ratio sqrt(m_i/m_e) = 43. The simulation was completed to full saturation in 334,000 CPU hours.
Simulations utilized resources of the National Energy Research Scientific Computing Center, operated under US DOE Contract No. DE-AC02-05CH11231, and the PSFC Engaging Cluster. This work is supported by US DOE Contract No. DE-FC02-08ER54966 and the SciDAC Partnership for Multiscale Gyrokinetic Turbulence, US DOE Contract No. DE-SC0018429 (Subaward No. UTA18- 000276).
