@Article{CiCP-19-205,
author = {Jean-Noel G. Leboeuf, Viktor K. Decyk, David E. Newman and Raul Sanchez},
title = {Implementation of 2D Domain Decomposition in the UCAN Gyrokinetic Particle-in-Cell Code and Resulting Performance of UCAN2},
journal = {Communications in Computational Physics},
year = {2018},
volume = {19},
number = {1},
pages = {205--225},
abstract = {<p style="text-align: justify;">The massively parallel, nonlinear, three-dimensional (3D), toroidal, electrostatic,
gyrokinetic, particle-in-cell (PIC), Cartesian geometry UCAN code, with particle
ions and adiabatic electrons, has been successfully exercised to identify non-diffusive
transport characteristics in present day tokamak discharges. The limitation in applying
UCAN to larger scale discharges is the 1D domain decomposition in the toroidal (or
z-) direction for massively parallel implementation using MPI which has restricted the
calculations to a few hundred ion Larmor radii or gyroradii per plasma minor radius.
To exceed these sizes, we have implemented 2D domain decomposition in UCAN with
the addition of the y-direction to the processor mix. This has been facilitated by use
of relevant components in the P2LIB library of field and particle management routines
developed for UCLA&#39;s UPIC Framework of conventional PIC codes. The gyro-averaging
specific to gyrokinetic codes is simplified by the use of replicated arrays
for efficient charge accumulation and force deposition. The 2D domain-decomposed
UCAN2 code reproduces the original 1D domain nonlinear results within round-off.
Benchmarks of UCAN2 on the Cray XC30 Edison at NERSC demonstrate ideal scaling
when problem size is increased along with processor number up to the largest power
of 2 available, namely 131,072 processors. These particle weak scaling benchmarks
also indicate that the 1 nanosecond per particle per time step and 1 TFlops barriers are
easily broken by UCAN2 with 1 billion particles or more and 2000 or more processors.</p>},
issn = {1991-7120},
doi = {https://doi.org/10.4208/cicp.070115.030715a},
url = {http://global-sci.org/intro/article_detail/cicp/11086.html}
}