Chicane with ISR
This is the Berlin-Zeuthen magnetic bunch compression chicane example, but this time with incoherent synchrotron radiation (CSR) modelled in the bending magnets. Coherent synchrotron radiation (CSR) is turned off.
All parameters can be found online. A 5 GeV electron bunch with normalized transverse rms emittance of 1 um undergoes longitudinal compression by a factor of 10 in a standard 4-bend chicane. The rms pulse length should decrease by the compression factor (10).
In this test, the initial and final values of \(\sigma_x\), \(\sigma_y\), \(\sigma_t\), \(\epsilon_x\), \(\epsilon_y\), and \(\epsilon_t\) must agree with nominal values.
Run
This example can be run either as:
Python script:
python3 run_chicane_isr.pyorImpactX executable using an input file:
impactx input_chicane_isr.in
For MPI-parallel runs, prefix these lines with mpiexec -n 4 ... or srun -n 4 ..., depending on the system.
#!/usr/bin/env python3
#
# Copyright 2022-2023 ImpactX contributors
# Authors: Marco Garten, Axel Huebl, Chad Mitchell
# License: BSD-3-Clause-LBNL
#
# -*- coding: utf-8 -*-
from impactx import ImpactX, distribution, elements
sim = ImpactX()
# set numerical parameters and IO control
sim.space_charge = False
sim.isr = True
# sim.diagnostics = False # benchmarking
sim.slice_step_diagnostics = True
# domain decomposition & space charge mesh
sim.init_grids()
# load a 5 GeV electron beam with an initial
# normalized transverse rms emittance of 1 um
kin_energy_MeV = 5.0e3 # reference energy
bunch_charge_C = 1.0e-9 # used with space charge
npart = 10000 # number of macro particles
# reference particle
ref = sim.particle_container().ref_particle()
ref.set_charge_qe(-1.0).set_mass_MeV(0.510998950).set_kin_energy_MeV(kin_energy_MeV)
# particle bunch
distr = distribution.Waterbag(
lambdaX=2.2951017632e-5,
lambdaY=1.3084093142e-5,
lambdaT=5.5555553e-8,
lambdaPx=1.598353425e-6,
lambdaPy=2.803697378e-6,
lambdaPt=2.000000000e-6,
muxpx=0.933345606203060,
muypy=0.933345606203060,
mutpt=0.999999961419755,
)
sim.add_particles(bunch_charge_C, distr, npart)
# add beam diagnostics
monitor = elements.BeamMonitor("monitor", backend="h5")
# design the accelerator lattice
ns = 25 # number of slices per ds in the element
rc = 10.3462283686195526 # bend radius (meters)
psi = 0.048345620280243 # pole face rotation angle (radians)
lb = 0.500194828041958 # bend arc length (meters)
# Drift elements
dr1 = elements.Drift(name="dr1", ds=5.0058489435, nslice=ns)
dr2 = elements.Drift(name="dr2", ds=1.0, nslice=ns)
dr3 = elements.Drift(name="dr3", ds=2.0, nslice=ns)
# Bend elements
sbend1 = elements.Sbend(name="sbend1", ds=lb, rc=-rc, nslice=ns)
sbend2 = elements.Sbend(name="sbend2", ds=lb, rc=rc, nslice=ns)
# Dipole Edge Focusing elements
dipedge1 = elements.DipEdge(name="dipedge1", psi=-psi, rc=-rc, g=0.0, K2=0.0)
dipedge2 = elements.DipEdge(name="dipedge2", psi=psi, rc=rc, g=0.0, K2=0.0)
lattice_half = [sbend1, dipedge1, dr1, dipedge2, sbend2]
# assign a segment with the first half of the lattice
sim.lattice.append(monitor)
sim.lattice.extend(lattice_half)
sim.lattice.append(dr2)
lattice_half.reverse()
# extend the lattice by a reversed half
sim.lattice.extend(lattice_half)
sim.lattice.append(dr3)
sim.lattice.append(monitor)
# run simulation
sim.track_particles()
# clean shutdown
sim.finalize()
###############################################################################
# Particle Beam(s)
###############################################################################
beam.npart = 10000
beam.units = static
beam.kin_energy = 5.0e3
beam.charge = 1.0e-9
beam.particle = electron
beam.distribution = gaussian
beam.lambdaX = 2.2951017632e-5
beam.lambdaY = 1.3084093142e-5
beam.lambdaT = 5.5555553e-8
beam.lambdaPx = 1.598353425e-6
beam.lambdaPy = 2.803697378e-6
beam.lambdaPt = 2.000000000e-6
beam.muxpx = 0.933345606203060
beam.muypy = beam.muxpx
beam.mutpt = 0.999999961419755
###############################################################################
# Beamline: lattice elements and segments
###############################################################################
lattice.elements = monitor sbend1 dipedge1 drift1 dipedge2 sbend2 drift2 \
sbend2 dipedge2 drift1 dipedge1 sbend1 drift3 monitor
lattice.nslice = 25
sbend1.type = sbend
sbend1.ds = 0.500194828041958 # projected length 0.5 m, angle 2.77 deg
sbend1.rc = -10.3462283686195526
drift1.type = drift
drift1.ds = 5.0058489435 # projected length 5 m
sbend2.type = sbend
sbend2.ds = 0.500194828041958 # projected length 0.5 m, angle 2.77 deg
sbend2.rc = 10.3462283686195526
drift2.type = drift
drift2.ds = 1.0
drift3.type = drift
drift3.ds = 2.0
dipedge1.type = dipedge # dipole edge focusing
dipedge1.psi = -0.048345620280243
dipedge1.rc = -10.3462283686195526
dipedge1.g = 0.0
dipedge1.K2 = 0.0
dipedge2.type = dipedge
dipedge2.psi = 0.048345620280243
dipedge2.rc = 10.3462283686195526
dipedge2.g = 0.0
dipedge2.K2 = 0.0
monitor.type = beam_monitor
monitor.backend = h5
###############################################################################
# Algorithms
###############################################################################
algo.space_charge = false
algo.isr = true
###############################################################################
# Diagnostics
###############################################################################
diag.slice_step_diagnostics = true
Analyze
We run the following script to analyze correctness:
Script analysis_chicane_isr.py
#!/usr/bin/env python3
#
# Copyright 2022-2023 ImpactX contributors
# Authors: Axel Huebl, Chad Mitchell
# License: BSD-3-Clause-LBNL
#
import numpy as np
import openpmd_api as io
from scipy.stats import moment
def get_moments(beam):
"""Calculate standard deviations of beam position & momenta
and emittance values
Returns
-------
sigx, sigy, sigt, emittance_x, emittance_y, emittance_t
"""
sigx = moment(beam["position_x"], moment=2) ** 0.5 # variance -> std dev.
sigpx = moment(beam["momentum_x"], moment=2) ** 0.5
sigy = moment(beam["position_y"], moment=2) ** 0.5
sigpy = moment(beam["momentum_y"], moment=2) ** 0.5
sigt = moment(beam["position_t"], moment=2) ** 0.5
sigpt = moment(beam["momentum_t"], moment=2) ** 0.5
epstrms = beam.cov(ddof=0)
emittance_x = (sigx**2 * sigpx**2 - epstrms["position_x"]["momentum_x"] ** 2) ** 0.5
emittance_y = (sigy**2 * sigpy**2 - epstrms["position_y"]["momentum_y"] ** 2) ** 0.5
emittance_t = (sigt**2 * sigpt**2 - epstrms["position_t"]["momentum_t"] ** 2) ** 0.5
return (sigx, sigy, sigt, emittance_x, emittance_y, emittance_t)
# initial/final beam
series = io.Series("diags/openPMD/monitor.h5", io.Access.read_only)
last_step = list(series.iterations)[-1]
initial = series.iterations[1].particles["beam"].to_df()
final = series.iterations[last_step].particles["beam"].to_df()
# compare number of particles
num_particles = 10000
assert num_particles == len(initial)
assert num_particles == len(final)
print("Initial Beam:")
sigx, sigy, sigt, emittance_x, emittance_y, emittance_t = get_moments(initial)
print(f" sigx={sigx:e} sigy={sigy:e} sigt={sigt:e}")
print(
f" emittance_x={emittance_x:e} emittance_y={emittance_y:e} emittance_t={emittance_t:e}"
)
atol = 0.0 # ignored
rtol = 2.2 * num_particles**-0.5 # from random sampling of a smooth distribution
print(f" rtol={rtol} (ignored: atol~={atol})")
assert np.allclose(
[sigx, sigy, sigt, emittance_x, emittance_y, emittance_t],
[
6.4214719960819659e-005,
3.6603372435649773e-005,
1.9955175623579313e-004,
1.0198263116327677e-010,
1.0308359092878036e-010,
4.0035161705244885e-010,
],
rtol=rtol,
atol=atol,
)
print("")
print("Final Beam:")
sigx, sigy, sigt, emittance_x, emittance_y, emittance_t = get_moments(final)
print(f" sigx={sigx:e} sigy={sigy:e} sigt={sigt:e}")
print(
f" emittance_x={emittance_x:e} emittance_y={emittance_y:e} emittance_t={emittance_t:e}"
)
atol = 0.0 # ignored
rtol = 2.6 * num_particles**-0.5 # from random sampling of a smooth distribution
print(f" rtol={rtol} (ignored: atol~={atol})")
assert np.allclose(
[sigx, sigy, sigt, emittance_x, emittance_y, emittance_t],
[
2.461167e-05,
8.390282e-05,
2.000320e-05,
1.048590e-10,
1.021730e-10,
2.068807e-09,
],
rtol=rtol,
atol=atol,
)