Plotting buildup results

These figures show the beam profile, electron cloud buildup, and wall impacts in an LHC dipole simulation. The macroparticle diagnostics and horizontal distributions provide a closer look at the simulation.

Beam and electron population

Beam density, cloud population, wall impacts, and secondary emission

lam_t_array shows the beam line density and Nel_timep the electron population per metre. Nel_imp_time and Nel_emit_time count impacts and emissions accumulated over each saved interval, also per metre. Divide by the saved interval duration to express these counts as rates.

Energy and central density

Deposited, emitted, and kinetic energy, and central density

En_imp_eV_time and En_emit_eV_time give the weighted energy of impacting and emitted electrons during each saved interval. En_kin_eV_time is the energy of the cloud at the saved time. These energies are normalized per metre along the beam. cen_density measures the volume density near the chamber centre, within the radius set by r_center.

Macroparticle diagnostics

Macroparticle counts, impacts, tracking corrections, and reference weight

N_mp_pass counts simulation macroparticles, while N_mp_ref_pass records their reference weight. N_mp_impact_pass and N_mp_corrected_pass track impacts and tracking corrections during each passage.

Histograms by passage and position

The horizontal histograms have shape (number of passages, number of bins). Rows correspond to t_hist; columns correspond to xg_hist.

from PyECLOUD.myloadmat_to_obj import myloadmat_to_obj

data = myloadmat_to_obj("Pyecltest.mat")
electrons_per_passage = data.nel_hist.sum(axis=1)
population_sum_by_position = data.nel_hist.sum(axis=0)

Summing over bins (axis=1) gives one value per recorded passage:

Cloud population, scrubbing impacts, all impacts, and deposited energy per passage

Summing over passages (axis=0) gives the accumulated horizontal distribution:

Horizontal distributions summed over recorded passages

For nel_hist, this sum combines population snapshots: the same electron can contribute at several passages. It is not a count of distinct electrons. For the impact histograms, it combines impacts recorded across the passages. nel_impact_hist_scrub selects impacts above scrub_en_th.

The plotted values are per bin. Divide by the bin width to obtain a density per unit horizontal position, or by the number of records to average snapshots.

Reproduce these plots

The figures use the saved LHC dipole reference data from the original manual:

testing/tests_buildup/LHC_ArcDipReal_450GeV_sey1.70_2.5e11ppb_bl_1.00ns/Pyecltest_angle3D_ref.mat

Download plot_buildup_outputs.py and pass this file’s path to regenerate the figures. To plot your own output, run it beside Pyecltest.mat:

python plot_buildup_outputs.py Pyecltest.mat

The script writes five SVG figures to buildup-plots/ using the fields shown on this page. The output reference describes these fields and how to load them with myloadmat_to_obj. Results from a new run can differ with the software version, input settings, and random particle sampling.