import numpy as np
import scipy.constants as const
import matplotlib.pyplot as plt

x = np.loadtxt('emit_vs_x.txt')
V0 = 1
U = V0 - x[:,2]
q = const.e
m = 40*const.m_u
v = np.sqrt(2*q*U/m)

plt.plot(x[:,0],1e6*x[:,1]*v/const.c)
plt.xlabel('x (m)')
plt.ylabel('RMS emittance (mm mrad)')
plt.savefig('emit_vs_x.eps')
plt.show()