The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
We present an example of our computations on a shock wave refracting from CO2 into CH4. The resul... more We present an example of our computations on a shock wave refracting from CO2 into CH4. The results are compared with the experiments of Abdel‐Fattah and Henderson. Our input data was the same as the parameters they measured and we used the same boundaries. We also took into account the mutal gas contamination present in the experiments and the effects of a separating membrane. All the principle properties of a free‐precursor refraction were detected.
Author(s): Friedman, Alex; Davidson, Ronald C.; Welch, Dale R.; Cohen, Ronald H.; Grote, David P.... more Author(s): Friedman, Alex; Davidson, Ronald C.; Welch, Dale R.; Cohen, Ronald H.; Grote, David P.; Sharp, William M.; Colella, Phillip; Vay, Jean-Luc; Yu, Simon S.; Lee, W. Wei-li; Qin, Hong; Rose, David V.; O'Shea, Patrick G.; Kishek, Rami A.; Haber, Irving
2018 IEEE 25th International Conference on High Performance Computing Workshops (HiPCW), 2018
We propose FFTX, a new framework for building high-performance FFT-based applications on exascale... more We propose FFTX, a new framework for building high-performance FFT-based applications on exascale machines. Complex node architectures lead to multiple levels of parallelism and demand efficient ways of data communication. The current FFTW interface falls short in maximizing performance in such scenarios. FFTX is designed to enable application developers to leverage expert-level, automatic optimizations while navigating a familiar interface. FFTX is backwards compatible to FFTW and extends the FFTW Interface into an embedded Domain Specific Language (DSL) expressed as a library interface. By means of a SPIRAL-based back end, this enables build-time source-to-source translation and advanced performance optimizations, such as cross-library calls optimizations, targeting of accelerators through offload-ing, and inlining of user-provided kernels. We demonstrate the use of FFTX with the prototypical example of 1D and 3D pruned convolutions and discuss future extensions.
The development of the continuum gyrokinetic code COGENT for edge plasma simulations is reported.... more The development of the continuum gyrokinetic code COGENT for edge plasma simulations is reported. The present version of the code models a nonlinear axisymmetric 4D (R, v∥, μ) gyrokinetic equation coupled to the long-wavelength limit of the gyro-Poisson equation. Here, R is the particle gyrocenter coordinate in the poloidal plane, and v∥ and μ are the guiding center velocity parallel to the magnetic field and the magnetic moment, respectively. The COGENT code utilizes a fourth-order finite-volume (conservative) discretization combined with arbitrary mapped multiblock grid technology (nearly field-aligned on blocks) to handle the complexity of tokamak divertor geometry with high accuracy. Topics presented are the implementation of increasingly detailed model collision operators, and the results of neoclassical transport simulations including the effects of a strong radial electric field characteristic of a tokamak pedestal under H-mode conditions.
ABSTRACT Geodesic acoustic modes (GAMs) are an important phenomenon in a tokamak edge plasma. The... more ABSTRACT Geodesic acoustic modes (GAMs) are an important phenomenon in a tokamak edge plasma. They regulate turbulence in a low confinement (L-mode) regime and can play an important role in the low to high (L–H) mode transition. It is therefore of considerable importance to develop a detailed theoretical understanding of their dynamics and relaxation processes. The present work reports on the numerical modelling of collisionless GAM relaxation, including the effects of a strong radial electric field characteristic of a tokamak pedestal in a high confinement (H-mode) regime. The simulations demonstrate that the presence of a strong radial electric field enhances the GAM decay rate, and heuristic arguments elucidating this finding are provided. The numerical modelling is performed by making use of the continuum gyrokinetic code COGENT.
The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
We present an example of our computations on a shock wave refracting from CO2 into CH4. The resul... more We present an example of our computations on a shock wave refracting from CO2 into CH4. The results are compared with the experiments of Abdel‐Fattah and Henderson. Our input data was the same as the parameters they measured and we used the same boundaries. We also took into account the mutal gas contamination present in the experiments and the effects of a separating membrane. All the principle properties of a free‐precursor refraction were detected.
Author(s): Friedman, Alex; Davidson, Ronald C.; Welch, Dale R.; Cohen, Ronald H.; Grote, David P.... more Author(s): Friedman, Alex; Davidson, Ronald C.; Welch, Dale R.; Cohen, Ronald H.; Grote, David P.; Sharp, William M.; Colella, Phillip; Vay, Jean-Luc; Yu, Simon S.; Lee, W. Wei-li; Qin, Hong; Rose, David V.; O'Shea, Patrick G.; Kishek, Rami A.; Haber, Irving
2018 IEEE 25th International Conference on High Performance Computing Workshops (HiPCW), 2018
We propose FFTX, a new framework for building high-performance FFT-based applications on exascale... more We propose FFTX, a new framework for building high-performance FFT-based applications on exascale machines. Complex node architectures lead to multiple levels of parallelism and demand efficient ways of data communication. The current FFTW interface falls short in maximizing performance in such scenarios. FFTX is designed to enable application developers to leverage expert-level, automatic optimizations while navigating a familiar interface. FFTX is backwards compatible to FFTW and extends the FFTW Interface into an embedded Domain Specific Language (DSL) expressed as a library interface. By means of a SPIRAL-based back end, this enables build-time source-to-source translation and advanced performance optimizations, such as cross-library calls optimizations, targeting of accelerators through offload-ing, and inlining of user-provided kernels. We demonstrate the use of FFTX with the prototypical example of 1D and 3D pruned convolutions and discuss future extensions.
The development of the continuum gyrokinetic code COGENT for edge plasma simulations is reported.... more The development of the continuum gyrokinetic code COGENT for edge plasma simulations is reported. The present version of the code models a nonlinear axisymmetric 4D (R, v∥, μ) gyrokinetic equation coupled to the long-wavelength limit of the gyro-Poisson equation. Here, R is the particle gyrocenter coordinate in the poloidal plane, and v∥ and μ are the guiding center velocity parallel to the magnetic field and the magnetic moment, respectively. The COGENT code utilizes a fourth-order finite-volume (conservative) discretization combined with arbitrary mapped multiblock grid technology (nearly field-aligned on blocks) to handle the complexity of tokamak divertor geometry with high accuracy. Topics presented are the implementation of increasingly detailed model collision operators, and the results of neoclassical transport simulations including the effects of a strong radial electric field characteristic of a tokamak pedestal under H-mode conditions.
ABSTRACT Geodesic acoustic modes (GAMs) are an important phenomenon in a tokamak edge plasma. The... more ABSTRACT Geodesic acoustic modes (GAMs) are an important phenomenon in a tokamak edge plasma. They regulate turbulence in a low confinement (L-mode) regime and can play an important role in the low to high (L–H) mode transition. It is therefore of considerable importance to develop a detailed theoretical understanding of their dynamics and relaxation processes. The present work reports on the numerical modelling of collisionless GAM relaxation, including the effects of a strong radial electric field characteristic of a tokamak pedestal in a high confinement (H-mode) regime. The simulations demonstrate that the presence of a strong radial electric field enhances the GAM decay rate, and heuristic arguments elucidating this finding are provided. The numerical modelling is performed by making use of the continuum gyrokinetic code COGENT.
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Papers by Phillip Colella