desc.magnetic_fields.CurrentPotentialField

class desc.magnetic_fields.CurrentPotentialField(potential, potential_dtheta, potential_dzeta, params=None, R_lmn=None, Z_lmn=None, modes_R=None, modes_Z=None, NFP=1, sym='auto', M=None, N=None, name='', check_orientation=True)Source

Magnetic field due to a surface current potential on a toroidal surface.

Surface current K is assumed given by K = n x ∇ Φ where:

• n is the winding surface unit normal.

• Phi is the current potential function, which is a function of theta and zeta.

This function then uses biot-savart to find the B field from this current density K on the surface.

Parameters:

• potential (callable) – function to compute the current potential. Should have a signature of the form potential(theta,zeta,**params) -> ndarray. theta,zeta are poloidal and toroidal angles on the surface

• potential_dtheta (callable) – function to compute the theta derivative of the current potential

• potential_dzeta (callable) – function to compute the zeta derivative of the current potential

• params (dict, optional) – default parameters to pass to potential function (and its derivatives)

• R_lmn (array-like, shape(k,)) – Fourier coefficients for winding surface R and Z in cylindrical coordinates

• Z_lmn (array-like, shape(k,)) – Fourier coefficients for winding surface R and Z in cylindrical coordinates

• modes_R (array-like, shape(k,2)) – poloidal and toroidal mode numbers [m,n] for R_lmn.

• modes_Z (array-like, shape(k,2)) – mode numbers associated with Z_lmn, defaults to modes_R

• NFP (int) – number of field periods

• sym (bool) – whether to enforce stellarator symmetry for the surface geometry. Default is “auto” which enforces if modes are symmetric. If True, non-symmetric modes will be truncated.

• M (int or None) – Maximum poloidal and toroidal mode numbers. Defaults to maximum from modes_R and modes_Z.

• N (int or None) – Maximum poloidal and toroidal mode numbers. Defaults to maximum from modes_R and modes_Z.

• name (str) – name for this field

• check_orientation (bool) – ensure that this surface has a right handed orientation. Do not set to False unless you are sure the parameterization you have given is right handed (ie, e_theta x e_zeta points outward from the surface).

Methods

change_resolution(*args, **kwargs)	Change the maximum poloidal and toroidal resolution.
compute(names[, grid, params, transforms, ...])	Compute the quantity given by name on grid.
compute_Bnormal(surface[, eval_grid, ...])	Compute Bnormal from self on the given surface.
compute_magnetic_field(coords[, params, ...])	Compute magnetic field at a set of points.
constant_offset_surface(offset[, grid, M, ...])	Create a FourierRZSurface with constant offset from the base surface (self).
copy([deepcopy])	Return a (deep)copy of this object.
equiv(other)	Compare equivalence between DESC objects.
from_input_file(path)	Create a surface from Fourier coefficients in a DESC or VMEC input file.
from_qp_model([major_radius, aspect_ratio, ...])	Create a surface from a near-axis model for quasi-poloidal symmetry.
from_surface(surface, potential, ...[, params])	Create CurrentPotentialField using geometry provided by given surface.
from_values(coords, theta[, zeta, M, N, ...])	Create a surface from given R,Z coordinates in real space.
get_coeffs(m[, n])	Get Fourier coefficients for given mode number(s).
load(load_from[, file_format])	Initialize from file.
pack_params(p)	Convert a dictionary of parameters into a single array.
save(file_name[, file_format, file_mode])	Save the object.
save_BNORM_file(surface, fname[, basis_M, ...])	Create BNORM-style .txt file containing Bnormal Fourier coefficients.
save_mgrid(path, Rmin, Rmax, Zmin, Zmax[, ...])	Save the magnetic field to an mgrid NetCDF file in "raw" format.
set_coeffs(m[, n, R, Z])	Set specific Fourier coefficients.
unpack_params(x)	Convert a single array of concatenated parameters into a dictionary.

Attributes

L	Maximum radial mode number.
M	Maximum poloidal mode number.
N	Maximum toroidal mode number.
NFP	Number of (toroidal) field periods.
R_basis	Spectral basis for R.
R_lmn	Spectral coefficients for R.
Z_basis	Spectral basis for Z.
Z_lmn	Spectral coefficients for Z.
dim_x	total number of optimizable parameters.
dimensions	dictionary of integers of sizes of each optimizable parameter.
name	Name of the surface.
optimizable_params	string names of parameters that have been declared optimizable.
params	Dict of parameters to pass to potential function and its derivatives.
params_dict	dictionary of arrays of optimizable parameters.
potential	Potential function, signature (theta,zeta,**params) -> potential value.
potential_dtheta	Phi poloidal deriv.
potential_dzeta	Phi toroidal deriv.
rho	Flux surface label.
sym	Whether or not the surface is stellarator symmetric.
x_idx	arrays of indices for each parameter in concatenated array.