EPOCH Post-Processing Script

A standalone Python script for visualizing EPOCH quasi-3D laser wakefield acceleration (LWFA) simulations. Generates animated 2-panel visualizations showing plasma density with laser field overlay and density-colored phase space.

What It Does

Takes raw EPOCH SDF output files and creates an interactive HTML animation:

Panel	Shows
Top	Electron density (grayscale) with laser field overlay (pink), dual colorbars
Bottom	Longitudinal phase space colored by local density, with momentum lineout

Quick Start

1. Install

pip install -r requirements.txt

You also need sdf_helper from EPOCH:

cd /path/to/epoch/epoch2d
make sdfutils
export PYTHONPATH="/path/to/epoch/epoch2d/SDF/utilities:$PYTHONPATH"

2. Run

Copy the script to your EPOCH output directory and run:

cd /path/to/your/epoch/output
cp /path/to/Post-processing-PIC/post-process-lwfa.py .
python post-process-lwfa.py

3. View Results

Open post-process-output/lwfa_q3d_animation.html in a web browser.

Configuration

Edit the CONFIG dictionary at the top of post-process-lwfa.py:

CONFIG = {
    # Your simulation parameters
    'lambda0_um': 1.0,          # Laser wavelength [μm]
    'a0': 3.0,                  # Normalized vector potential
    'n_over_nc': 0.0025,        # Plasma density / critical density

    # File patterns (EPOCH default naming)
    'efield_pattern': 'E_field{:04d}.sdf',
    'ener_pattern': 'ener{:04d}.sdf',
    'dens_pattern': 'dens*.sdf',

    # Particle species name in your simulation
    'species': 'He_electron',

    # Visualization settings
    'downsample_x': 10,         # Reduce data for faster plotting
    'density_vmin': 1e-4,       # Density color range (log scale)
    'density_vmax': 1.0,
    'field_vmax': 5.0,          # Field overlay range
    'ps_density_bins': (100, 100),  # Phase space density resolution
}

How It Works

1. Find frames: Scans directory for SDF files matching the pattern
2. Load data: For each frame, loads 3 files:
   • E_field*.sdf → Electric field modes and grid
   • dens*.sdf → Electron density
   • ener*.sdf → Particle data (positions, momenta, weights)
3. Normalize: Converts to physical units (lengths in λ₀, density in n_c, etc.)
4. Visualize: Creates animated 2-panel plot with colorbars and lineouts
5. Save: Outputs HTML animation + NumPy arrays for reuse

Output Files

In post-process-output/:

• lwfa_q3d_animation.html - Interactive animation (open in browser)
• lwfa_q3d_*.npy - Processed data arrays for custom plotting

Requirements

• Python 3.9+
• NumPy, SciPy, Matplotlib
• sdf_helper (compiled from EPOCH)

License

MIT License