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#! /usr/bin/env python
'''
Analysis script of a WarpX simulation of rigid injection in a boosted frame.
A Gaussian electron beam starts from -5 microns, propagates rigidly up to
20 microns after which it expands due to emittance only (the focal position is
20 microns). The beam width is measured after ~50 microns, and compared with
the theory (with a 5% error allowed).
The simulation runs in a boosted frame, and the analysis is done in the lab
frame, i.e., on the back-transformed diagnostics.
'''
import sys, os, yt, glob
import numpy as np
import scipy.constants as scc
import read_raw_data
yt.funcs.mylog.setLevel(0)
# filename = sys.argv[1]
def get_particle_field(snapshot, species, field):
fn = snapshot + '/' + species
files = glob.glob(os.path.join(fn, field + '_*'))
files.sort()
all_data = np.array([])
for f in files:
data = np.fromfile(f)
all_data = np.concatenate((all_data, data))
return all_data
# Read data from back-transformed diagnostics
snapshot = './lab_frame_data/snapshot00001'
header = './lab_frame_data/Header'
allrd, info = read_raw_data.read_lab_snapshot(snapshot, header)
z = np.mean( get_particle_field(snapshot, 'beam', 'z') )
w = np.std ( get_particle_field(snapshot, 'beam', 'x') )
# initial parameters
z0 = 20.e-6
w0 = 1.e-6
theta0 = np.arcsin(0.1)
# Theoretical beam width after propagation if rigid ON
wth = np.sqrt( w0**2 + (z-z0)**2*theta0**2 )
error = np.abs((w-wth)/wth)
# Print error and assert small error
print("Beam position: " + str(z))
print("Beam width : " + str(w))
print("error: " + str(error))
assert( error < 0.03 )
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