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
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| a_b | Scope: restricted | REAL |
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| Description: Magnetic field strength parameter.
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| Range | | Default: 1e-3 |
| *:* | Any real
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| afield_type | Scope: restricted | KEYWORD |
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| Description: A-field prescription
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| Range | | Default: TOV_pressure_prescription |
| see [1] below | A_phi propto (P - P_cut)  _s |
| see [1] below | A_phi propto rho
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| see [1] below | Dipole magnetic field, interior to the star
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| see [1] below | Dipole magnetic field everywhere
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[1]
TOV\_pressure\_prescription
[1]
TOV\_density\_prescription
[1]
BNS\_poloidal\_A\_interior
[1]
BNS\_dipolar\_A\_everywhere
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| enable_illinoisgrmhd_staggered_a_fields | Scope: restricted | BOOLEAN |
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| Description: Define A fields on an IllinoisGRMHD staggered grid
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| | | Default: yes |
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| enable_varpi_squared_multiplication | Scope: restricted | BOOLEAN |
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Description: Multiply A_phi by varpi ?
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| | | Default: yes |
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| have_two_nss_along_x_axis | Scope: restricted | BOOLEAN |
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| Description: Do we have two NSs centered along x-axis?
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| | | Default: no |
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| i_zero_ns1 | Scope: restricted | REAL |
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| Description: Magnetic field loop current of NS1.
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| Range | | Default: 0.0 |
| 0.0:*) |
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| i_zero_ns2 | Scope: restricted | REAL |
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| Description: Magnetic field loop current of NS2.
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| Range | | Default: 0.0 |
| 0.0:*) |
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| n_s | Scope: restricted | REAL |
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| Description: Magnetic field strength pressure exponent.
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| Range | | Default: 1.0 |
| *:* | Any real
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| p_cut | Scope: restricted | REAL |
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| Description: Cutoff pressure, below which vector potential is set to zero. Typically set to 4% of
the maximum initial pressure.
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| Range | | Default: 1e-5 |
| 0:* | Positive
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| r_ns1 | Scope: restricted | REAL |
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| Description: Radius of NS1. Does not have to be perfect, but must not overlap other star.
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| Range | | Default: 13.5 |
| 0:* | Any positive
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| r_ns2 | Scope: restricted | REAL |
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| Description: Radius of NS2. Does not have to be perfect, but must not overlap other star.
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| Range | | Default: 13.5 |
| 0:* | Any positive
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| r_zero_ns1 | Scope: restricted | REAL |
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| Description: Current loop radius of NS1.
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| Range | | Default: 1.0 |
| 0.0:*) |
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| r_zero_ns2 | Scope: restricted | REAL |
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| Description: Current loop radius of NS2.
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| Range | | Default: 1.0 |
| 0.0:*) |
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| rho_cut | Scope: restricted | REAL |
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| Description: Cutoff density, below which vector potential is set to zero. Typically set to 20% of
the maximum initial density.
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| Range | | Default: 0.2 |
| 0:* | Positive
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| x_c1 | Scope: restricted | REAL |
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| Description: x coordinate of NS1 center
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| Range | | Default: -15.2 |
| *:* | Any real
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| x_c2 | Scope: restricted | REAL |
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| Description: x coordinate of NS2 center
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| Range | | Default: 15.2 |
| *:* | Any real
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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] | |
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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) |
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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) |
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Aliased Functions
| Alias Name: | Function Name: |
| Seed_Magnetic_Fields_BNS | Seed_Magnetic_Fields |
| Seed_Magnetic_Fields_TOV | Seed_Magnetic_Fields |
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