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.. _developers-qed:
QED
====================
Quantum synchrotron
-------------------
.. note::
Section empty!
Breit-Wheeler
-------------
.. note::
Section empty!
Schwinger process
-----------------
If the code is compiled with QED and the user activates the Schwinger process in the input file,
electron-positron pairs can be created in vacuum in the function
``MultiParticleContainer::doQEDSchwinger``:
.. doxygenfunction:: MultiParticleContainer::doQEDSchwinger
``MultiParticleContainer::doQEDSchwinger`` in turn calls the function ``filterCreateTransformFromFAB``:
.. doxygenfunction:: filterCreateTransformFromFAB(DstTile&, DstTile&, const amrex::Box, const FABs&, const Index, const Index, FilterFunc&&, CreateFunc1&&, CreateFunc2&&, TransFunc&&)
``filterCreateTransformFromFAB`` proceeds in three steps.
In the filter phase, we loop on every cell and calculate the number of physical pairs created within
the time step dt as a function of the electromagnetic field at the given cell position.
This probabilistic calculation is done via a wrapper that calls the ``PICSAR`` library.
In the create phase, the particles are created at the desired positions, currently at the cell nodes.
In the transform phase, we assign a weight to the particles depending on the number of physical
pairs created.
At most one macroparticle is created per cell per timestep per species, with a weight corresponding to
the total number of physical pairs created.
So far the Schwinger module requires using ``warpx.do_nodal=1`` or
``algo.field_gathering=momentum-conserving`` (so that the auxiliary fields are calculated on the nodes)
and is not compatible with either mesh refinement, RZ coordinates or single precision.
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