.. _examples-bend-isr:

A Single Bend with ISR
=======================

This test illustrates the effects of incoherent synchrotron radiation (ISR) on a high-energy electron bunch in a bending dipole.  The effects of CSR are turned off.

An initially cold (zero emittance), 100 GeV electron bunch with a 0.1 mm rms beam size propagates in an ideal sector bend, through a region of uniform magnetic field.

Due to the stochastic emission of synchrotron radiation, the bunch experiences a mean loss of energy as well as a growth in rms energy spread.  Due to the presence of nonzero dispersion,
this also results in a growth of the bunch rms emittance.

The resulting quantities are compared against the expressions given in:

N. Yampolsky and B. Carlsten, "Beam debunching due to ISR-induced energy diffusion," Nucl. Instrum. and Methods in Phys. Res. A,
870, 156-162 (2017), equations (17-20).

In this test, the values of :math:`\langle{p_x\rangle}`, :math:`\langle{p_y\rangle}`, :math:`\langle{p_t\rangle}`, :math:`\sigma_{p_x}`, :math:`\sigma_{p_y}`, and :math:`\sigma_{p_t}` must agree with nominal values.

In addition, the final values of :math:`\langle{p_t\rangle}` and :math:`\sigma_{p_t}` must agree with predicted values.


Run
---

This example can be run **either** as:

* **Python** script: ``python3 run_bend_isr.py`` or
* ImpactX **executable** using an input file: ``impactx input_bend_isr.in``

For `MPI-parallel <https://www.mpi-forum.org>`__ runs, prefix these lines with ``mpiexec -n 4 ...`` or ``srun -n 4 ...``, depending on the system.

.. tab-set::

   .. tab-item:: Python: Script

       .. literalinclude:: run_bend_isr.py
          :language: python3
          :caption: You can copy this file from ``examples/incoherent_synchrotron/run_bend_isr.py``.

   .. tab-item:: Executable: Input File

       .. literalinclude:: input_bend_isr.in
          :language: ini
          :caption: You can copy this file from ``examples/incoherent_synchrotron/input_bend_isr.in``.

Analyze
-------

We run the following script to analyze correctness:

.. dropdown:: Script ``analysis_bend_isr.py``

   .. literalinclude:: analysis_bend_isr.py
      :language: python3
      :caption: You can copy this file from ``examples/incoherent_synchrotron/analysis_bend_isr.py``.


.. _examples-bend-isr-ref:

A Single Bend with ISR, Reference Energy Loss
=============================================

This is identical to the preceding test, except for the flag ``isr_on_ref_part`` option being enabled.  In this test, the reference particle experiences radiative energy loss.  For the beam particles,
whose coordinates and momenta are measured relative to the reference particle, the primary effect of ISR is to induce an increase in energy spread.  Little effect is visible on
the beam centroid.


Run
---

This example can be run **either** as:

* **Python** script: ``python3 run_bend_isr_ref.py`` or
* ImpactX **executable** using an input file: ``impactx input_bend_isr_ref.in``

For `MPI-parallel <https://www.mpi-forum.org>`__ runs, prefix these lines with ``mpiexec -n 4 ...`` or ``srun -n 4 ...``, depending on the system.

.. tab-set::

   .. tab-item:: Python: Script

       .. literalinclude:: run_bend_isr_ref.py
          :language: python3
          :caption: You can copy this file from ``examples/incoherent_synchrotron/run_bend_isr_ref.py``.

   .. tab-item:: Executable: Input File

       .. literalinclude:: input_bend_isr_ref.in
          :language: ini
          :caption: You can copy this file from ``examples/incoherent_synchrotron/input_bend_isr_ref.in``.

Analyze
-------

We run the following script to analyze correctness:

.. dropdown:: Script ``analysis_bend_isr_ref.py``

   .. literalinclude:: analysis_bend_isr_ref.py
      :language: python3
      :caption: You can copy this file from ``examples/incoherent_synchrotron/analysis_bend_isr_ref.py``.