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#!/usr/bin/env python3
# Copyright 2021 David Grote
#
# This file is part of WarpX.
#
# License: BSD-3-Clause-LBNL
"""
This script tests the plasma lens.
The input file sets up a series of plasma lens and propagates two particles through them.
One particle is in the X plane, the other the Y plane.
The final positions are compared to the analytic solutions.
The motion is slow enough that relativistic effects are ignored.
"""
import os
import sys
import numpy as np
from scipy.constants import c, e, m_e
import yt
yt.funcs.mylog.setLevel(0)
sys.path.insert(1, '../../../../warpx/Regression/Checksum/')
import checksumAPI
filename = sys.argv[1]
ds = yt.load( filename )
ad = ds.all_data()
# Get final position of the particles.
# There are two particles, one moves in x, the other in y.
# The particles may not be in order, so determine which is which
# by looking at their max positions in the respective planes.
i0 = np.argmax(np.abs(ad['electrons', 'particle_position_x'].v))
i1 = np.argmax(np.abs(ad['electrons', 'particle_position_y'].v))
xx_sim = ad['electrons', 'particle_position_x'].v[i0]
yy_sim = ad['electrons', 'particle_position_y'].v[i1]
zz_sim0 = ad['electrons', 'particle_position_z'].v[i0]
zz_sim1 = ad['electrons', 'particle_position_z'].v[i1]
ux_sim = ad['electrons', 'particle_momentum_x'].v[i0]/m_e
uy_sim = ad['electrons', 'particle_momentum_y'].v[i1]/m_e
if 'warpx.gamma_boost' in ds.parameters:
gamma_boost = float(ds.parameters.get('warpx.gamma_boost'))
uz_boost = np.sqrt(gamma_boost*gamma_boost - 1.)*c
time = ds.current_time.to_value()
zz_sim0 = gamma_boost*zz_sim0 + uz_boost*time
zz_sim1 = gamma_boost*zz_sim1 + uz_boost*time
def applylens(x0, vx0, vz0, gamma, lens_length, lens_strength):
kb0 = np.sqrt(e/(m_e*gamma*vz0**2)*lens_strength)
x1 = x0*np.cos(kb0*lens_length) + (vx0/vz0)/kb0*np.sin(kb0*lens_length)
vx1 = vz0*(-kb0*x0*np.sin(kb0*lens_length) + (vx0/vz0)*np.cos(kb0*lens_length))
return x1, vx1
clight = c
try:
vel_z = eval(ds.parameters.get('my_constants.vel_z'))
except TypeError:
# vel_z is not saved in my_constants with the PICMI version
vel_z = 0.5*c
plasma_lens_period = float(ds.parameters.get('particles.repeated_plasma_lens_period'))
plasma_lens_starts = [float(x) for x in ds.parameters.get('particles.repeated_plasma_lens_starts').split()]
plasma_lens_lengths = [float(x) for x in ds.parameters.get('particles.repeated_plasma_lens_lengths').split()]
plasma_lens_strengths_E = [eval(x) for x in ds.parameters.get('particles.repeated_plasma_lens_strengths_E').split()]
plasma_lens_strengths_B = [eval(x) for x in ds.parameters.get('particles.repeated_plasma_lens_strengths_B').split()]
x0 = float(ds.parameters.get('electrons.multiple_particles_pos_x').split()[0])
y0 = float(ds.parameters.get('electrons.multiple_particles_pos_y').split()[1])
z0 = float(ds.parameters.get('electrons.multiple_particles_pos_z').split()[0])
ux0 = float(ds.parameters.get('electrons.multiple_particles_vel_x').split()[0])*c
uy0 = float(ds.parameters.get('electrons.multiple_particles_vel_y').split()[1])*c
uz0 = eval(ds.parameters.get('electrons.multiple_particles_vel_z').split()[0])*c
tt = 0.
xx = x0
yy = y0
zz = z0
ux = ux0
uy = uy0
uz = uz0
gamma = np.sqrt(uz0**2/c**2 + 1.)
vz = uz/gamma
for i in range(len(plasma_lens_starts)):
z_lens = i*plasma_lens_period + plasma_lens_starts[i]
vx = ux/gamma
vy = uy/gamma
dt = (z_lens - zz)/vz
tt = tt + dt
xx = xx + dt*vx
yy = yy + dt*vy
lens_strength = plasma_lens_strengths_E[i] + plasma_lens_strengths_B[i]*vel_z
xx, vx = applylens(xx, vx, vz, gamma, plasma_lens_lengths[i], lens_strength)
yy, vy = applylens(yy, vy, vz, gamma, plasma_lens_lengths[i], lens_strength)
dt = plasma_lens_lengths[i]/vz
tt = tt + dt
ux = gamma*vx
uy = gamma*vy
zz = z_lens + plasma_lens_lengths[i]
dt0 = (zz_sim0 - zz)/vz
dt1 = (zz_sim1 - zz)/vz
vx = ux/gamma
vy = uy/gamma
xx = xx + dt0*vx
yy = yy + dt1*vy
print(f'Error in x position is {abs(np.abs((xx - xx_sim)/xx))}, which should be < 0.02')
print(f'Error in y position is {abs(np.abs((yy - yy_sim)/yy))}, which should be < 0.02')
print(f'Error in x velocity is {abs(np.abs((ux - ux_sim)/ux))}, which should be < 0.002')
print(f'Error in y velocity is {abs(np.abs((uy - uy_sim)/uy))}, which should be < 0.002')
assert abs(np.abs((xx - xx_sim)/xx)) < 0.02, Exception('error in x particle position')
assert abs(np.abs((yy - yy_sim)/yy)) < 0.02, Exception('error in y particle position')
assert abs(np.abs((ux - ux_sim)/ux)) < 0.002, Exception('error in x particle velocity')
assert abs(np.abs((uy - uy_sim)/uy)) < 0.002, Exception('error in y particle velocity')
test_name = os.path.split(os.getcwd())[1]
checksumAPI.evaluate_checksum(test_name, filename)
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