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:

\begin {eqnarray} A_x &=& -y*A_b*pow(MAX(P-P_cut,0.0),n_s) \\ A_y &=& x*A_b*pow(MAX(P-P_cut,0.0),n_s) \\ A_z &=& 0 \\ Phi &=& 0 \end {eqnarray}

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 \(A_i\)’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: TOV_pressure_prescription
see [1] below
A_phi propto (P - P_cut)ˆn  _s
see [1] below
A_phi propto rho
see [1] below
Dipole magnetic field, interior to the star
see [1] below
Dipole magnetic field everywhere



[1]

TOV\_pressure\_prescription

[1]

TOV\_density\_prescription

[1]

BNS\_poloidal\_A\_interior

[1]

BNS\_dipolar\_A\_everywhere




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 varpiˆ2  ?



  Default: yes






have_two_nss_along_x_axis
Scope: restricted  BOOLEAN



Description: Do we have two NSs centered along x-axis?



  Default: no






i_zero_ns1
Scope: restricted  REAL



Description: Magnetic field loop current of NS1.



Range   Default: 0.0
0.0:*)






i_zero_ns2
Scope: restricted  REAL



Description: Magnetic field loop current of NS2.



Range   Default: 0.0
0.0:*)






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






r_ns1
Scope: restricted  REAL



Description: Radius of NS1. Does not have to be perfect, but must not overlap other star.



Range   Default: 13.5
0:*
Any positive






r_ns2
Scope: restricted  REAL



Description: Radius of NS2. Does not have to be perfect, but must not overlap other star.



Range   Default: 13.5
0:*
Any positive






r_zero_ns1
Scope: restricted  REAL



Description: Current loop radius of NS1.



Range   Default: 1.0
0.0:*)






r_zero_ns2
Scope: restricted  REAL



Description: Current loop radius of NS2.



Range   Default: 1.0
0.0:*)






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






x_c1
Scope: restricted  REAL



Description: x coordinate of NS1 center



Range   Default: -15.2
*:*
Any real






x_c2
Scope: restricted  REAL



Description: x coordinate of NS2 center



Range   Default: 15.2
*:*
Any real



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 (conditional)

  seed_magnetic_fields_tov

  set up tov seed magnetic fields.

 

 After: hydrobase_initial
 Before: illinoisgrmhd_id_converter
   hydrobase_prim2coninitial
 Language:c
 Reads: grid::x
   grid::y
   hydrobase::rho
   hydrobase::press
 Type: function
 Writes: hydrobase::avec(everywhere)
   hydrobase::aphi(everywhere)

CCTK_INITIAL (conditional)

  seed_magnetic_fields_bns

  set up binary neutron star seed magnetic fields.

 

 After: hydrobase_initial
 Before: illinoisgrmhd_id_converter
   hydrobase_prim2coninitial
 Language:c
 Reads: grid::x
   grid::y
   grid::z
   hydrobase::press
 Type: function
 Writes: hydrobase::avec(everywhere)
   hydrobase::aphi(everywhere)

Aliased Functions

 

Alias Name:         Function Name:
Seed_Magnetic_Fields_BNS Seed_Magnetic_Fields
Seed_Magnetic_Fields_TOVSeed_Magnetic_Fields