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Beam tab

Configure the input beam: species, energy, current, distribution, Twiss, centroid offsets, mismatch, halo. Maps 1-to-1 to BeamConfig fields.

Beam tab

Beam tab — particle/energy/current group, per-plane Twiss, centroid & mismatch, and the four-panel phase-space preview.

Layout

The tab is three fixed group boxes side by side, a four-panel phase-space preview underneath, and a button row at the bottom — nothing collapses:

  • Particle · Energy · RF · Current — species dropdown, W_kin (MeV), f_rf (MHz), peak current (mA), duty cycle (%), N particles, distribution dropdown, cutoff (σ), the halo controls, and the DC / continuous-beam controls (Continuous beam checkbox + DC ΔW energy spread).
  • Twiss — X / Y / Z — ε_nx, α_x, β_x, ε_ny, α_y, β_y, ε_z, α_z, β_z.
  • Centroid · Mismatch · Derived — read-only derived β / γ / βγ for the current species + energy, deterministic centroid offsets (δx, δx', δy, δy', δφ, δW), and fractional emittance mismatch (Δ ε_x / Δ ε_y / Δ ε_z, %).

The halo fraction and halo σ ratio fields are always visible but enabled only when the distribution is thermal (bi-Gaussian); they grey out for every other distribution.

Initial phase-space preview

The Initial phase-space preview group shows four log-intensity 2-D density panels of a sample beam: x–x', y–y', φ–dW, and the real-space x–y view (which surfaces transverse coupling / mismatch at a glance). Regenerate preview redraws it from the current form values.

Button row

  • Apply — build a BeamConfig from the form and commit it to the app state (see below).
  • Regenerate preview — refresh the four preview panels.
  • Reset defaults — restore every field to its default value.
  • Import .dst… — see next section.

Importing a .dst distribution

The Import .dst… button reads a TraceWin .dst particle file (there is no format selector — .dst is the import format). The file's header auto-populates the form: energy, frequency, current, particle count, and the calculated ε / Twiss per plane. The simulation then reads the actual particles from the file (source="file") instead of regenerating from Twiss. A file chip appears next to the button naming the active .dst, with a clear link that reverts to generate-from-Twiss mode.

DC vs bunched mode

For pre-RFQ LEBTs:

  1. Set continuous = True.
  2. Set emit_z = 0 (no longitudinal structure).
  3. Optional: set DC energy spread (keV).

Forgetting continuous=True produces non-physical σ_φ blow-up; see DC mode.

Tooltips

Hover any field to see its meaning, units, and typical value range. The full reference lives at BeamConfig field reference.

Apply and the project dirty flag

Beam config lives in the .lgproj JSON file, not the lattice .dat. Clicking Apply marks the project as dirty so the close prompt warns you if you've changed beam parameters but not yet saved the project. Internal beam updates (project load, matched-beam apply from the Matching tab) are explicitly marked clean — only your direct clicks of Apply flag the project as dirty. See Lattice tab → Unsaved-changes prompts.

Cross-references

← Lattice tab · Continue to Numerics tab →