steam-tfm

Transfer Function Model (TFM) of superconducting magnets, part of the STEAM framework at CERN.

Given a built LEDET magnet model, the TFM computes the magnet's passive coupling effects and writes an equivalent frequency-dependent circuit library (.lib) that a circuit simulator (PSPICE / XYCE) can use in place of a plain inductor:

• persistent currents (PC)
• inter-filament coupling currents (IFCC)
• inter-strand coupling currents (ISCC)
• eddy currents (ED)
• coupling with the passive structures: wedges, cold bore (CB), cold pipe support (CPS), aluminium ring (AlRing) and beam screen (BS)
• inter-turn shorts and capacitance to ground

This package was extracted from steam_sdk (steam_sdk.builders.BuilderTFM and steam_sdk.data.DataTFM) so the model, its tests and its release cycle stand on their own, the same way steam-roxie-parser was split out earlier.

Installation

pip install steam-tfm

For development, install the pinned environment first (the pins are kept in lock-step with steam_sdk/requirements.txt so both packages coexist in one environment):

pip install -r requirements.txt
pip install -e .[test]

Usage

The model takes plain data, not a steam_sdk object. steam_sdk supplies it through steam_sdk.builders.adapter_TFM.ledet_to_tfm_input(builder_ledet):

from steam_tfm.builders.builder_tfm import BuilderTFM

builder_tfm = BuilderTFM(
    ledet_input=ledet_input,            # steam_tfm.data.tfm_input.TFM_LEDET_Input
    TFM_inputs=tfm_inputs,              # TFMClass: flags, temperature, B_nom_center, ...
    magnet_data=magnet_data,            # Magnet_TFM: apertures, C_ground, passive structures, ...
    local_library_path=library_path,    # magnet folder holding TFM_input/Field_Map_*.csv
    output_path=output_path,            # where the .lib is written
    library_name='MBRD_TFM',            # name of the generated .lib subcircuit
    domain='frequency',                 # or 'transient'
    flag_build=True,
)

Layout:

Tests

The suite is written with unittest.TestCase and runs with unittest-parallel (not pytest):

python -m unittest discover -s tests -p "test_*.py" -t .
# or in parallel (module level, about half the cores: every worker re-imports numba/sympy/scipy)
python -m unittest_parallel -t . -s tests -p "test_*.py" --level=module -j 4

The tests build BuilderTFM from a snapshot fixture (tests/input/MBRD_tfm_input.pkl) rather than from a steam_sdk model build, so they need neither steam_sdk nor a magnet library. Regenerate the fixture with python scripts/make_tfm_fixture.py [path-to-steam_sdk] after changing the input contract.

Tests that evaluate the coupling effects additionally read the per-magnet TFM field maps (TFM_input/Field_Map_*.csv, several GB) from the steam_models library, which is too large to vendor here. They locate it via STEAM_MODELS_PATH, a tests/input_from_steam_models submodule, a sibling steam_models checkout or a sibling steam_sdk checkout, and skip themselves when none is present.

License

GPL-3.0-only. Contact: steam-team@cern.ch