Smilei exchangeB ghost cells confusion

smilei_exchangeB_confusion.png

test.py

import math as m
import numpy as np

TkeV = 10
T = TkeV/511

dx = 0.5
dy = dx

Lx = 16
Ly = 4

dt = 0.75 * dx/m.sqrt(2.)

Tsim = 40 * dt

Main(
    geometry = "2Dcartesian",
    interpolation_order = 2,
    timestep = dt,
    simulation_time = Tsim,
    cell_length  = [dx,dy],
    grid_length = [Lx,Ly],
    number_of_patches = [4,1],
    EM_boundary_conditions = [ ["periodic"], ["periodic"] ],
    print_every = 1,
    solve_poisson = True,
    patch_arrangement = "linearized_XY",
)

strength = 10
size = 0.03

def whirl_x(x, y):
    # translate to center
    x -= Lx / 2
    y -= Ly / 2

    len = np.sqrt(x**2 + y**2)
    taper = np.fmin(1.0, size * Ly / len if len > 0 else 1.0)
    return strength * taper * -y / len

def whirl_y(x, y):
    # translate to center
    x -= Lx / 2
    y -= Ly / 2

    len = np.sqrt(x**2 + y**2)
    taper = np.fmin(1.0, size * Lx / len if len > 0 else 1.0)
    return strength * taper * x / len

ExternalField(
    field = "Ex",
    profile = whirl_x
)

ExternalField(
    field = "Ey",
    profile = whirl_y
)

Species(
    name = "electron",
    position_initialization = "regular",
    momentum_initialization = "mj",
    particles_per_cell = 9,
    c_part_max = 1.0,
    mass = 1.0,
    charge = -1.0,
    charge_density = 1.0,
    mean_velocity = [0.0, 0.0, 0.0],
    temperature = [T],
    pusher = "boris",
    boundary_conditions = [["periodic"], ["periodic"]],
)

DiagFields(
    every = 2
)

DiagScalar(
    every = 1
)