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api_fields.rst

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Magnetic Fields and Coils

There are a number of ways for representing arbitrary magnetic fields in the lab (R, \phi, Z) frame. Their common characteristic is a compute_magnetic_field method allowing evaluation of \mathbf{B} at points in space.

Magnetic Fields

The desc.magnetic_fields module contains classes representing a number of standard field configurations, as well as classes for combining and scaling these fields. For interfacing with MAKEGRID type files, the SplineMagneticField class has a from_mgrid option allowing you to load an mgrid file and interpolate where needed. All MagneticField objects also have a save_mgrid method to save field data so that it can be read by VMEC and STELLOPT. They also have a compute_Bnormal method which accepts a surface and computes the normal field strength on that surface.

.. autosummary::
    :toctree: _api/magnetic_fields
    :recursive:
    :template: class.rst

    desc.magnetic_fields.SplineMagneticField
    desc.magnetic_fields.DommaschkPotentialField
    desc.magnetic_fields.ScalarPotentialField
    desc.magnetic_fields.ToroidalMagneticField
    desc.magnetic_fields.VerticalMagneticField
    desc.magnetic_fields.PoloidalMagneticField
    desc.magnetic_fields.ScaledMagneticField
    desc.magnetic_fields.SumMagneticField

There are also classes for representing a current potential on a winding surface:

.. autosummary::
    :toctree: _api/magnetic_fields
    :recursive:
    :template: class.rst

    desc.magnetic_fields.CurrentPotentialField
    desc.magnetic_fields.FourierCurrentPotentialField

There is also a class for representing omnigenous magnetic fields:

.. autosummary::
    :toctree: _api/magnetic_fields
    :recursive:
    :template: class.rst

    desc.magnetic_fields.OmnigenousField

For analyzing the structure of magnetic fields, it is often useful to find the trajectories of magnetic field lines, which can be done via desc.magnetic_fields.field_line_integrate.

.. autosummary::
    :toctree: _api/magnetic_fields
    :recursive:
    :template: class.rst

    desc.magnetic_fields.field_line_integrate

desc.magnetic_fields also contains a utility function for reading output files from the BNORM code:

.. autosummary::
    :toctree: _api/magnetic_fields
    :recursive:
    :template: class.rst

    desc.magnetic_fields.read_BNORM_file

Coils

Coil objects in desc.coils are themselves subclasses of MagneticField, allowing them to be used anywhere that expects a magnetic field type. There are a number of parameterizations based on the Curve classes defined in desc.geometry (which, since they are based on Curve classes, can also use the same Curve conversion methods to convert between coil representations):

.. autosummary::
    :toctree: _api/coils/
    :recursive:
    :template: class.rst

    desc.coils.FourierRZCoil
    desc.coils.FourierXYZCoil
    desc.coils.FourierPlanarCoil
    desc.coils.SplineXYZCoil

There are also objects for holding a collection of coils with efficient methods for evaluating the combined field. A CoilSet must consist of members with the same parameterization, while a MixedCoilSet can contain arbitrary types (including another CoilSet).

.. autosummary::
    :toctree: _api/coils/
    :recursive:
    :template: class.rst

    desc.coils.CoilSet
    desc.coils.MixedCoilSet

DESC CoilSet or MixedCoilSet objects can also be created from MAKEGRID-formatted coil text files via the from_makegrid_coilfile method. They can also be saved in a MAKEGRID-formatted text file with the save_in_makegrid_format method.