simsopt.mhd package

Submodules

simsopt.mhd.boozer module

This module provides a class that handles the transformation to Boozer coordinates, and an optimization target for quasisymmetry.

class simsopt.mhd.boozer.Boozer(equil: simsopt.mhd.vmec.Vmec, mpol: int = 32, ntor: int = 32)

Bases: simsopt._core.optimizable.Optimizable

This class handles the transformation to Boozer coordinates.

A Boozer instance maintains a set “s”, which is a registry of the surfaces on which other objects want Boozer-coordinate data. When the run() method is called, the Boozer transformation is carried out on all these surfaces. The registry can be cleared at any time by setting the s attribute to {}.

get_dofs()

This base Optimizable object has no degrees of freedom, so return an empty array

register(s: Union[float, Iterable[float]]) → None

This function is called by objects that depend on this Boozer object, to indicate that they will want Boozer data on the given set of surfaces.

Parameters

s – 1 or more surfaces on which Boozer data will be requested.

run()

Run booz_xform on all the surfaces that have been registered.

set_dofs(x)

This base Optimizable object has no degrees of freedom, so do nothing.

class simsopt.mhd.boozer.Quasisymmetry(boozer: simsopt.mhd.boozer.Boozer, s: Union[float, Iterable[float]], m: int, n: int, normalization: str = 'B00', weight: str = 'even')

Bases: simsopt._core.optimizable.Optimizable

This class is used to compute the departure from quasisymmetry on a given flux surface based on the Boozer spectrum.

Parameters

• boozer – A Boozer object on which the calculation will be based.

• s – The normalized toroidal magnetic flux for the flux surface to analyze. Should be in the range [0, 1].

• m – The poloidal mode number of the symmetry you want to achive. The departure from symmetry B(m * theta - nfp * n * zeta) will be reported.

• n – The toroidal mode number of the symmetry you want to achieve. The departure from symmetry B(m * theta - nfp * n * zeta) will be reported.

• normalization – A uniform normalization applied to all bmnc harmonics. If "B00", the symmetry-breaking modes will be divided by the m=n=0 mode amplitude on the same surface. If "symmetric", the symmetry-breaking modes will be divided by the square root of the sum of the squares of all the symmetric modes on the same surface. This is the normalization used in stellopt.

• weight – An option for a m- or n-dependent weight to be applied to the bmnc amplitudes.

J() → numpy.ndarray

Carry out the calculation of the quasisymmetry error.

Returns

1D numpy array listing all the normalized mode amplitudes of symmetry-breaking Fourier modes of |B|.

get_dofs()

This base Optimizable object has no degrees of freedom, so return an empty array

set_dofs(x)

This base Optimizable object has no degrees of freedom, so do nothing.

simsopt.mhd.spec module

This module provides a class that handles the SPEC equilibrium code.

class simsopt.mhd.spec.Residue(spec, pp, qq, vol=1, theta=0, s_guess=None, s_min=- 1.0, s_max=1.0, rtol=1e-09)

Bases: simsopt._core.optimizable.Optimizable

Greene’s residue, evaluated from a Spec equilibrum

J()

Run Spec if needed, find the periodic field line, and return the residue

get_dofs()

This base Optimizable object has no degrees of freedom, so return an empty array

set_dofs(x)

This base Optimizable object has no degrees of freedom, so do nothing.

class simsopt.mhd.spec.Spec(filename=None, exe='xspec')

Bases: simsopt._core.optimizable.Optimizable

This class represents the SPEC equilibrium code.

Philosophy regarding mpol and ntor: The Spec object keeps track of mpol and ntor values that are independent of those for the boundary Surface object. If the Surface object has different mpol/ntor values, the Surface’s rbc/zbs arrays are first copied, then truncated or expanded to fit the mpol/ntor values of the Spec object to before Spec is run. Therefore, you may sometimes need to manually change the mpol and ntor values for the Spec object.

get_dofs()

This base Optimizable object has no degrees of freedom, so return an empty array

iota()

Return the rotational transform in the middle of the volume.

run()

Run SPEC, if needed.

set_dofs(x)

This base Optimizable object has no degrees of freedom, so do nothing.

update_resolution(mpol, ntor)

For convenience, to save “.nml”

volume()

Return the volume inside the VMEC last closed flux surface.

simsopt.mhd.spec.nested_lists_to_array(ll)

Convert a ragged list of lists to a 2D numpy array. Any entries that are None are replaced by 0.

This function is applied to the RBC and ZBS arrays in the input namelist.

simsopt.mhd.vmec module

This module provides a class that handles the VMEC equilibrium code.

class simsopt.mhd.vmec.Vmec(filename: Optional[str] = None, mpi: Optional[simsopt.util.mpi.MpiPartition] = None)

Bases: simsopt._core.optimizable.Optimizable

This class represents the VMEC equilibrium code.

The input parameters to VMEC are all accessible as attributes of the indata attribute. For example, if vmec is an instance of Vmec, then you can read or write the input resolution parameters using vmec.indata.mpol, vmec.indata.ntor, vmec.indata.ns_array, etc. However, the boundary surface is different: rbc, rbs, zbc, and zbs from the indata attribute are always ignored, and these arrays are instead taken from the simsopt surface object associated to the boundary attribute. If boundary is a surface based on some other representation than VMEC’s Fourier representation, the surface will automatically be converted to VMEC’s representation (SurfaceRZFourier) before each run of VMEC. You can replace boundary with a new surface object, of any type that implements the conversion function ``to_RZFourier()`.

VMEC is run either when the run() function is called, or when any of the output functions like aspect() or iota_axis() are called.

A caching mechanism is implemented, using the attribute need_to_run_code. Whenever VMEC is run, this attribute is set to False. Subsequent calls to run() or output functions like aspect() will not actually run VMEC again, until need_to_run_code is changed to True. The attribute need_to_run_code is automatically set to True whenever set_dofs() is called. However, need_to_run_code is not automatically set to True when entries of indata are modified, or when boundary is modified.

Once VMEC has run at least once, all of the quantities in the wout output file are available as attributes of the wout attribute. For example, if vmec is an instance of Vmec, then the flux surface shapes can be obtained from vmec.wout.rmnc and vmec.wout.zmns.

Since the underlying fortran implementation of VMEC uses global module variables, it is not possible to have more than one python Vmec object with different parameters; changing the parameters of one would change the parameters of the other.

An instance of this class owns just a few optimizable degrees of freedom, particularly phiedge and curtor. The optimizable degrees of freedom associated with the boundary surface are owned by that surface object.

Parameters

• filename – Name of a VMEC input file to use for loading the initial parameters. If None, default parameters will be used.

• mpi – A simsopt.util.mpi.MpiPartition instance, from which the worker groups will be used for VMEC calculations. If None, each MPI process will run VMEC independently.

__repr__()

Print the object in an informative way.

aspect()

Return the plasma aspect ratio.

get_dofs()

This base Optimizable object has no degrees of freedom, so return an empty array

get_max_mn()

Look through the rbc and zbs data in fortran to determine the largest m and n for which rbc or zbs is nonzero.

iota_axis()

Return the rotational transform on axis

iota_edge()

Return the rotational transform at the boundary

load_wout()

Read in the most recent wout file created, and store all the data in a wout attribute of this Vmec object.

run()

Run VMEC, if need_to_run_code is True.

set_dofs(x)

This base Optimizable object has no degrees of freedom, so do nothing.

volume()

Return the volume inside the VMEC last closed flux surface.

Module contents