plasma oscillation in 1-D epoch

[Deepa64]

I am trying to perform plasma oscillation using 1-D epoch code. However, there is no density evolution occur in the output. kindly help me in digging out the error. I am attaching it input file here.

begin:control
nx = 30000
x_min = 0
x_max = 2*pi
npart = 100 * nx
t_end = 1.77e-8
end:control

begin:boundaries
bc_x_min = periodic
bc_x_max = periodic
end:boundaries

begin:constant
den_peak = 1.0e18
end:constant

begin:species
name = Electron
density = den_peak*((0.1cos(2pi*x/length_x))+1)
charge = -1.0
mass = 1.0
frac = 0.5
end:species

begin:species
name = Proton
density = den_peak
charge = 1.0
mass = 1836.2
frac = 0.5
end:species

begin:output

number of timesteps between output dumps

dt_snapshot = 1.77e-11

Number of dt_snapshot between full dumps

full_dump_every = 1

Properties at particle positions

particles = always
px = always

Properties on grid

grid = always
ex = always
ey = always
ez = always
bx = always
by = always
bz = always
jx = always
ekbar = always
mass_density = never + species
charge_density = always
number_density = always + species

extended io

distribution_functions = always
end:output