MHD studies towards simulating White Dwarf Mergersusing Castro

Marıa G. Barrios Sazo

Stony Brook University

Castro

Castro is an AMR code that solves the compressible hydrodynamicequations for astrophysical flows

I conservation of mass ∂ρ∂t = −∇ · (ρuuu) + Sext,ρ

I conservation of momentum ∂(ρuuu)∂t = −∇ · (ρuuuuuu)−∇p + ρggg + Sext,ρuuu

I conservation of total energy∂(ρE)∂t = −∇ · (ρuuuE + puuu) + ρHnuc + ρuuu · ggg + Sext,ρE

User can supply EOS and reaction networks

Self gravity

Radiation, gray and multigroup FLD

Supports 1-d, 2-d and 3-d

CastroZingale et al. 2017

4 2 0 2 4x (km) ×104

4

2

0

2

4

y(k

m)

×104

10−1

100

101

102

103

104

105

106

107

ρ( g cm

3

)

WD merger showing 2-level gridstructure

Adaptive MeshRefinement, built onAMReX

Simultaneous refinementin space and time

Hybrid parallelism,MPI+OpenMP

Regression tests

Ongoing development forGPUs

Open Source

github.com/AMReX-Astro/Castro

Scaling

NERSC Cori

101 102

number of nodes

100

101

102

avg.

tim

e / s

tep

10000 20000 30000 40000 50000 60000number of threads

Castro 3-d wdmerger (hydro + Poisson gravity)

2563 gnu2563 intel

5123 gnu5123 intel

no AMRbase + one 4x level

Zingale et al. 2017

OLCF Titan

102 103 104

number of cores

100

101

102

avg.

tim

e / s

tep

Castro 3-d wdmerger (hydro + Poisson gravity)

2563

5123no AMRbase + one 4x level

0 20 40 60 80 100 120number of GPUs

0

20

40

60

80

100

120

zone

s/s u

pdat

ed

StarLord GPU performance

OLCF Summitdev

MHD – Algorithm

Assumes perfectly conducting fluid

Only electric fields induced by motion of magnetized fluid

Miniati et al. 2011

Numerical schemes must ensure ∇∇∇ ·BBB = 0

Magnetic field defined at face center

Electric field at cell edges updates it

MHD port to Castro

Integrating MHDsolver from Nyx(cosmology code)

Support generalEOS

Add species

Coupled withself-gravityconservative form

VerificationShock tube test problem solved using 256 and 800grid cells at t = 0.1 s.

White Dwarf mergers

Katz et. al. 2016

Presence of magnetic fieldsand effect on fluidinstabilities could drive ahotspot into a detonation

Include MHD in WD Mergersimulation

Continue with WD mergercalculations

Study feasibility ofthermonuclear detonation

Explore different initialmodels

I He layerI CO + He mergers

Investigate algorithmicimprovements

I Well-balanced schemewith rotation

I Self-consistent initialconditions

Timeline for next year

Sept. 2018 – Verification andoptimization of MHD solver

Oct. 2018 – Explore WD mergerinitial models

Jan. 2018 – MHD solver withgravity tested

Apr. 2019 – WD mergerinvestigation of self-consistent initialconditions

Summer. 2019 – WD mergersimulations with MHD andadditional physics

Other work

Contributing on GPUefforts

Other planned researchevents

BNL GPUHackathon, Sept.2018

SIAM CSEMinisymposiumpresentation, Feb.2019