pals2cosy 0.4.0

Convert PALS lattice files to COSY INFINITY FOX code

pals2cosy

Convert PALS lattice files to COSY INFINITY FOX code.

Supports the official PALS format (PALS: root with facility:/line: composition) with auto-detection from the root key. Also accepts a flat beamline: format with positioned elements.

Installation

pip install pals2cosy

Or for development:

pip install -e .

Requires Python 3.9+ and PyYAML (for YAML input).

Usage

# PALS FODO cell (auto-detected from PALS: root key)
pals2cosy examples/fodo.pals.yaml --ke 1000 --particle proton

# Write to file with fringe fields
pals2cosy beamline.pals.yaml -o output.fox --ke 40 --fr 1

# Select a specific BeamLine from the facility
pals2cosy lattice.pals.yaml --beamline fodo_cell --ke 1000

# Compute Twiss parameters (periodic lattices only)
pals2cosy lattice.pals.yaml --ke 1000 --particle proton --twiss

Options

Flag	Default	Description
-o FILE	stdout	Output FOX file
--ke FLOAT	from lattice	Kinetic energy (MeV)
--fr INT	0	Fringe field order (0=none, 1=Enge, 2=symplectic, 3=high-precision Enge)
--order INT	3	DA computation order
--dim INT	3	Phase-space dimensions (2 or 3)
--quad-aperture FLOAT	0.027	Quadrupole bore diameter (m)
--particle STR	from lattice	Particle type (see Supported particles)
--twiss	off	Append GT Twiss extraction (requires periodic lattice)
--mode STR	auto	Input format override
--beamline NAME	last	BeamLine to expand (official PALS only)
--no-comments	off	Omit element name comments in FOX output

Input format

PALS:
  version: null
  facility:
    - q1:
        kind: Quadrupole
        length: 1.0
        MagneticMultipoleP:
          Bn1: 1.0           # Pole-tip field (Tesla)
    - b1:
        kind: SBend
        length: 2.0
        BendP:
          g_ref: 0.5         # Bend strength (1/m)
          e1: 0.1            # Entrance edge angle (radians)
          e2: 0.2            # Exit edge angle (radians)
    - my_line:
        kind: BeamLine
        line:
          - q1
          - b1

See examples/fodo.pals.yaml for a complete FODO cell with inherit: and repeat:.

Element mapping

Input type	FOX command	Notes
Quadrupole (Bn1)	MQ L Bn1 r ;	Direct pole-tip field
Quadrupole (current)	MQ L {±G·I·r} r ;	Sign from polarity
Sextupole (Bn2)	MH L Bn2 r ;	Drift if Bn2 absent
Octupole (Bn3)	MO L Bn3 r ;	Drift if Bn3 absent
Multipole (Bn1–Bn5)	M5 L BQ BH BO BD BZ r ;	Up to dodecapole; drift if all absent
Solenoid (Bz)	CMS Bz D L ;	Drift if Bz absent
RFCavity	RF V 0 W PHI D ;	Drift if voltage/frequency absent
Wiggler/Undulator	WI B K L D 0 0 0 ;	Drift if field/period absent
SBend/RBend (no Enge)	DIL L θ g/2 e₁ 0 e₂ 0 ;
SBend/RBend (with Enge)	FC ..; DIL ..; FD ;
SBend (negative angle)	CB ; DIL ..; CB ;
BPM/OTR/Corrector	(skipped)	Zero-length

Supported particles

Name	FOX command	Notes
electron	RPE	Preset
proton	RPP	Preset
muon, mu-	RPMU	μ⁻ preset
mu+, antimuon	RP	μ⁺ via generic RP (RPMU hardcodes charge −1)
pion+, pi+	RPPI E 1	Preset with charge
pion-, pi-	RPPI E -1	Preset with charge
positron	RP	Generic
antiproton	RP	Generic
deuteron	RP	Generic
alpha	RP	Generic (⁴He²⁺)
carbon12	RP	Generic (¹²C⁶⁺)

Known limitations

• Drift fallback: All active elements fall back to drifts when their field parameters are absent.
• Enge coefficients: Maximum 6 coefficients per fringe field (COSY INFINITY FC command limit). Longer coefficient lists are truncated with a warning.
• Quad sign convention: The current-based quadrupole path (±G·I·r) uses an electron-specific sign convention (QPF→negative B, QPD→positive B). Proton beamlines should use Bn1 (pole-tip field) instead, which bypasses the sign logic.

Roadmap

pals2cosy implements provisional support for element types and parameters that are present in COSY INFINITY but not yet part of the official PALS specification, such as MagneticMultipoleP.Bn2–Bn5, SolenoidP.Bz, and RFCavityP. As a documented PALS use case, these extensions may inform future PALS standardization. If PALS adopts a different parameterization, pals2cosy can be adjusted accordingly.

Planned extensions:

• Combined-function magnets (dipole + multipole fields → COSY MC/MS)
• Electrostatic deflectors (EC, ECL, ES)
• Skew multipoles (MMS, EMS)
• Particle tracking (SR + TR + PRAY/WRAY)
• FIT optimization blocks

Acknowledgments

This work was supported in part by DOE EPSCoR Award DE-SC0025583. The converter is based in part on research performed on the University of Hawaiʻi free electron laser by the author.

Tests

pip install pytest
pytest tests/ -v