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

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:

$\begin{array}{rcll}{A}_{x}& =& -y\ast {A}_{b}\ast pow\left(MAX\left(P-{P}_{c}ut,0.0\right),{n}_{s}\right)& \text{(1)}\text{}\text{}\\ {A}_{y}& =& x\ast {A}_{b}\ast pow\left(MAX\left(P-{P}_{c}ut,0.0\right),{n}_{s}\right)& \text{(2)}\text{}\text{}\\ {A}_{z}& =& 0& \text{(3)}\text{}\text{}\\ Phi& =& 0& \text{(4)}\text{}\text{}\end{array}$

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

 enable_illinoisgrmhd_staggered_a_ﬁelds Scope: restricted BOOLEAN Description: Deﬁne A ﬁelds on an IllinoisGRMHD staggered grid 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

### 2 Interfaces

#### General

Implements:

seed_magnetic_ﬁelds

Inherits:

grid

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