Skip to content

Numerics tab

Configure tracking-step density and space-charge solver settings. Wraps SpaceChargeConfig and tracker-level integrator parameters in a single panel.

Numerics tab

Numerics tab — collapsible numerics sections plus the built-in convergence-scan controls.

Sections

The settings panel is grouped into seven collapsible sections; only "Step density" opens by default, and each section's open/closed state is persisted per user across sessions:

  • Step density — an Integration profile preset combo (Production (100/50) / Matching (30/15) / Custom — editing either spinbox by hand switches to Custom), plus base step1 (integration steps per metre) and step2 (SC kicks per metre). Map to TraceWin's PARTRAN_STEP step1 step2.
  • Space charge & PIC — Base PIC grid (nx=ny=nz): a single cubic spinbox (one value sets all three axes); grid extent (σ multiplier); PIC backend (auto / cpu / gpu / cuda / mps); SC engine — numpy (production PIC, default) or torch (the differentiable PyTorch PIC). Pick torch for the autograd-differentiable space-charge kick; it runs FP64 on CPU, handles bunched beams only, and is markedly slower. Selecting it greys out Grid mode, PIC backend and DC kernel (torch ignores them — it always uses an adaptive grid); a continuous beam falls back to numpy automatically. Also: Green's function (IGF / point), particle-mesh kernel (CIC / TSC), grid mode (fixed / adaptive), and the DC SC kernel (uniform / gaussian / pic2d) for continuous beams.
  • Field maps (FieldMap3D) — integrator (KD / DKD) and interpolation order (linear / cubic).
  • Envelope solver — solver choice: matrix (element-by-element transfer-matrix Σ propagation, default) or sacherer (coupled KV envelope ODE integrated with RK45; better under strong SC where the matrix split-operator under-resolves).
  • Collective effects — "CSR in bends" checkbox: apply a 1-D steady-state Coherent Synchrotron Radiation energy kick inside dipoles (multi-particle runs only — see Space-charge models → CSR).
  • Diagnostics & recording — record_substeps checkbox; Record particle density (histogram all alive particles into a 2-D density grid along s); Snapshot every N (full 6-D particle dump every N elements; 0 = only Marker(snapshot=True) fires); density bins and density extent (±mm) for the density recording.
  • Scan controls — Scan N particles (macroparticle count the convergence scans use) and Parallel workers (0 = serial; N > 1 fans scan points across processes).

Convergence scans

Convergence scans are built into this tab — no separate dialog. The Scan parameters group has:

  • Scan axis combo — grid (nx=ny=nz), grid_extent (σ), step1 (integration/m), step2 (SC kicks/m), or n_particles.
  • Values (comma-sep) field — the scan points; defaults to 32, 48, 64, 96, 128.

The run row below offers:

  • Run All Scans (grid · extent · step1 · step2) — scans all four PIC/step parameters in sequence and auto-applies the converged value for each axis as it finishes.
  • Run Single Axis — scan just the selected axis with the Values list.
  • Stop — halt at the next element boundary, keeping the rows already completed.
  • Apply converged value — write the converged row's scan value back into the base settings used by Run Multi-particle.

Results stream into a tabbed output pane: Log (per-axis convergence log), Plot (ε_x end + σ_y vs scan value), and Table (per-point σ_x / σ_y / σ_φ / ε_x / ε_y / wall time).

Tooltips with formula references

Each field has a tooltip explaining its meaning + the relevant physics paper. E.g. the IGF tooltip cites Qiang et al. 2006.

Project dirty tracking

Every "fixed" setting in this tab (PIC grid, SC engine, Green's function, particle-mesh kernel, integrator, interp, step1 / step2, CSR flag) is serialised into the .lgproj JSON. Changing any of them marks the project as dirty so closing without Save Project triggers a warning. Section-collapse toggles and scan-axis widgets don't flag the project — collapse states persist per user via QSettings instead, and the scan-axis widgets are session-only. See Lattice tab → Unsaved-changes prompts.

Cross-references

← Beam tab · Continue to Matching tab →