Seed_Magnetic_Fields: A Module for Seeding a Matter Distribution with Magnetic Fields

Original author: Zachariah B. Etienne.

Date: 2015-10-12 12:00:00 -0600 (Mon, 12 Oct 2015)

Abstract

The Seed_Magnetic_Fields thorn seeds magnetic fields into an initial hydrodynamic configuration. Currently seeding into TOV stars is supported, according to the poloidal magnetic field prescription:

Ax = y Ab pow(MAX(P Pcut,0.0),ns) (1) Ay = x Ab pow(MAX(P Pcut,0.0),ns) (2) Az = 0 (3) Phi = 0 (4)

as specified in Appendix B of the IllinoisGRMHD code announcement paper:
http://arxiv.org/pdf/1501.07276.pdf

Note that we must be careful if Ai’s are staggered. In this case, the pressure must be interpolated to the staggered point, and the values of x and y must also be shifted.

Both staggered and unstaggered vector potential fields are currently supported in this thorn.

1 Parameters




a_b
Scope: restricted  REAL



Description: Magnetic field strength parameter.



Range   Default: 1e-3
*:*
Any real






afield_type
Scope: restricted  KEYWORD



Description: A-field prescription



Range   Default: Pressure_prescription
see [1] below
A_phi propto (P - P_cut)n̂_s
see [1] below
A_phi propto rho



[1]

Pressure\_prescription

[1]

Density\_prescription




enable_illinoisgrmhd_staggered_a_fields
Scope: restricted  BOOLEAN



Description: Define A fields on an IllinoisGRMHD staggered grid



  Default: yes






enable_varpi_squared_multiplication
Scope: restricted  BOOLEAN



Description: Multiply A_phi by varpi2̂?



  Default: yes






n_s
Scope: restricted  REAL



Description: Magnetic field strength pressure exponent.



Range   Default: 1.0
*:*
Any real






p_cut
Scope: restricted  REAL



Description: Cutoff pressure, below which vector potential is set to zero. Typically set to 4% of the maximum initial pressure.



Range   Default: 1e-5
0:*
Positive






rho_cut
Scope: restricted  REAL



Description: Cutoff density, below which vector potential is set to zero. Typically set to 20% of the maximum initial density.



Range   Default: 0.2
0:*
Positive



2 Interfaces

General

Implements:

seed_magnetic_fields

Inherits:

grid

admbase

hydrobase

3 Schedule

This section lists all the variables which are assigned storage by thorn WVUThorns/Seed_Magnetic_Fields. Storage can either last for the duration of the run (Always means that if this thorn is activated storage will be assigned, Conditional means that if this thorn is activated storage will be assigned for the duration of the run if some condition is met), or can be turned on for the duration of a schedule function.

Storage

 

Always:  
HydroBase::rho[1] HydroBase::press[1] HydroBase::eps[1] HydroBase::vel[1] HydroBase::Bvec[1] HydroBase::Avec[1] HydroBase::Aphi[1] 
   

Scheduled Functions

CCTK_INITIAL

  seed_magnetic_fields

  set up seed magnetic field configuration.

 

 After: hydrobase_initial
 Before: illinoisgrmhd_id_converter
 Language:c
 Type: function