J. Hittinger
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View article: ZFP: A compressed array representation for numerical computations
ZFP: A compressed array representation for numerical computations Open
HPC trends favor algorithms and implementations that reduce data motion relative to FLOPS. We investigate the use of lossy compressed data arrays in place of traditional IEEE floating point arrays to store the primary data of calculations.…
View article: Global gyrokinetic simulations of ASDEX Upgrade up to the transport timescale with GENE–Tango
Global gyrokinetic simulations of ASDEX Upgrade up to the transport timescale with GENE–Tango Open
An accurate description of turbulence up to the transport timescale is essential for predicting core plasma profiles and enabling reliable calculations for designing advanced scenarios and future devices. Here, we exploit the gap separatio…
View article: LLNL Response to the DOE ASCR RFI, "Stewardship of Software for Scientific and High-Performance Computing"
LLNL Response to the DOE ASCR RFI, "Stewardship of Software for Scientific and High-Performance Computing" Open
For decades, Lawrence Livermore National Laboratory (LLNL) has been engaged in significant research, development, and support for software to enable scientific computing and, particularly, the use of high performance computing (HPC) in the…
View article: Numerical Simulation of Phase Space Advection in Gyrokinetic Models of Fusion Plasmas
Numerical Simulation of Phase Space Advection in Gyrokinetic Models of Fusion Plasmas Open
We describe our progress in the development of a fourth-order, finite-volume discretization of a nonlinear, full-f gyrokinetic Vlasov-Poisson system in mapped coordinates. The approach treats the configuration and velocity components of ph…
View article: Spatial coupling of gyrokinetic simulations, a generalized scheme based on first-principles
Spatial coupling of gyrokinetic simulations, a generalized scheme based on first-principles Open
We present a scheme that spatially couples two gyrokinetic codes using first-principles. Coupled equations are presented and a necessary and sufficient condition for ensuring accuracy is derived. This new scheme couples both the field and …
View article: Consistent coupling algorithms for coupled core-edge simulations of plasma turbulence
Consistent coupling algorithms for coupled core-edge simulations of plasma turbulence Open
Two schemes for coupling gyrokinetic simulations of microturbulence in tokamaks are proposed. The first scheme is based on an additive Schwarz domain decomposition. We show that, because the goal of turbulence is long-time averages of the …
View article: Stability Analysis of Inline ZFP Compression for Floating-Point Data in Iterative Methods
Stability Analysis of Inline ZFP Compression for Floating-Point Data in Iterative Methods Open
Currently, the dominating constraint in many high performance computing applications is data capacity and bandwidth, in both inter-node communications and even more-so in on-node data motion. A new approach to address this limitation is to…
View article: Variable Precision Computing
Variable Precision Computing Open
This report summarizes the activities and major accomplishments of the Variable Precision Computing Strategic Initiative project. The overarching goal of this project was to initiate and promote a new paradigm in High Performance Computing…
View article: Linearized Coulomb Collision Operator for Simulation of Interpenetrating Plasma Streams
Linearized Coulomb Collision Operator for Simulation of Interpenetrating Plasma Streams Open
We present an extension of a linearized Coulomb collision operator, previously used in several Eulerian kinetic codes for like-species collisions and unlike-species collisions in the case where the backgrounds about which the linearization…
View article: Error Analysis of ZFP Compression for Floating-Point Data
Error Analysis of ZFP Compression for Floating-Point Data Open
Compression of floating-point data will play an important role in high-performance computing as data bandwidth and storage become dominant costs. Lossy compression of floating-point data is powerful, but theoretical results are needed to b…
View article: High-order discretization of a gyrokinetic Vlasov model in edge plasma geometry
High-order discretization of a gyrokinetic Vlasov model in edge plasma geometry Open
We describe a new spatial discretization of a continuum gyrokinetic Vlasov model in axisymmetric tokamak edge plasma geometries. The geometries are represented using a multiblock decomposition in which logically distinct blocks are smoothl…
View article: Verification of 5D continuum gyrokinetic code COGENT: Studies of kinetic drift wave instability
Verification of 5D continuum gyrokinetic code COGENT: Studies of kinetic drift wave instability Open
COGENT (Continuum Gyrokinetic Edge New Technology) is a kinetic plasma simulation code that is being developed by the edge simulation laboratory (ESL) collaboration. The original version of the code has been developed in a 4D phase space (…
View article: Universal coding of the reals
Universal coding of the reals Open
We propose a modular framework for representing the real numbers that generalizes ieee, posits, and related floating-point number systems, and which has its roots in universal codes for the positive integers such as the Elias codes. This f…
View article: Bringing global gyrokinetic turbulence simulations to the transport timescale using a multiscale approach
Bringing global gyrokinetic turbulence simulations to the transport timescale using a multiscale approach Open
The vast separation dividing the characteristic times of energy confinement and turbulence in the core of toroidal plasmas makes first-principles prediction on long timescales extremely challenging. Here we report the demonstration of a mu…
View article: Bringing global gyrokinetic turbulence simulations to the transport timescale using a multiscale approach
Bringing global gyrokinetic turbulence simulations to the transport timescale using a multiscale approach Open
The vast separation dividing the characteristic times of energy confinement and turbulence in the core of toroidal plasmas makes first-principles prediction on long timescales extremely challenging. Here in this work, we report the demonst…
View article: Kinetic Simulation of Collisional Magnetized Plasmas with Semi-Implicit Time Integration
Kinetic Simulation of Collisional Magnetized Plasmas with Semi-Implicit Time Integration Open
Plasmas with varying collisionalities occur in many applications, such as tokamak edge regions, where the flows are characterized by significant variations in density and temperature. While a kinetic model is necessary for weakly-collision…
View article: On the arithmetic intensity of high-order finite-volume discretizations for hyperbolic systems of conservation laws
On the arithmetic intensity of high-order finite-volume discretizations for hyperbolic systems of conservation laws Open
It has been conjectured that higher-order discretizations for partial differential equations will have advantages over the lower-order counterparts commonly used today. The reasoning is that the increase in arithmetic operations will be mo…
View article: Continuum Gyrokinetic Edge New Technology
Continuum Gyrokinetic Edge New Technology Open
COGENT is a simulation code that models the plasma evolution in the edge region of a tokamak fusion reactor, from the open field line scrape-off layer, across the separatrix, and into the core. The model is based on the 4D gyrokinetic clos…