Data Analysis

Beam Monitor

ImpactX provides a zero-sized beam monitor element that can be placed in lattices to output the particle beam at multiple positions in a lattice. Output is written in the standardized, open particle-mesh data schema (openPMD) and is compatible with many codes and data analysis frameworks.

See also WarpX’ documentation on openPMD.

Reduced Beam Characteristics

ImpactX calculates reduced beam characteristics like averaged positions, momenta, beam emittances and Courant-Snyder (Twiss) parameters during runtime. These quantities are calculated before, after, and during each step of the simulation. If diag.slice_step_diagnostics is enabled, they will also be calculated during each slice of each beamline element.

The code writes out the values in an ASCII file prefixed reduced_beam_characteristics containing the follow columns:

• step

  Iteration within the simulation

• s, ref_beta_gamma

  Reference particle coordinate s and relativistic momentum normalized by the particle mass and the speed of light

• x_mean, y_mean, t_mean

  Average beam particle position in the dimensions of x, y (transverse coordinates), and t (normalized time difference)

• sig_x, sig_y, sig_t

  RMS of the average beam particle positions

• px_mean, py_mean, pt_mean

  Average beam momenta

• sig_px, sig_py, sig_pt

  RMS of the average beam momenta (energy difference for pt)

• emittance_x, emittance_y, emittance_t

  Normalized beam emittance

• alpha_x, alpha_y, alpha_t

  Twiss alpha

• beta_x, beta_y, beta_t

  Twiss beta

• charge

  Cumulated beam charge in C