File size increases after converting from .mat files to .txt files

I have a lot of .mat files which contain the information about the radial part of some different wavefunctions and some other information about an atom. Now I successfully extracted the wavefunction part and using numpy.savetxt() to save it into .txt file. But the size of the file increases so much: After I ran

    du -ch wfkt_X_rb87_n=40_L=11_J=0_step=0.001.mat
    440K    wfkt_X_rb87_n=40_L=11_J=0_step=0.001.mat
    du -ch wfkt_X_rb87_n=40_L=12_J=0_step=0.001.txt
    2,9M    wfkt_X_rb87_n=40_L=12_J=0_step=0.001.txt

Ignore the L=11 and L=12 difference, the size of the wavefunctions are almost the same, but the file size increased by more than 6 times. I want to know the reason why and probably a way to decrease the size of the .txt files. Here is the code how I covert the files:

    import scipy.io as sio
    import os
    import pickle
    import numpy as np
    import glob as gb
    files=gb.glob('wfkt_X_rb*.mat')
    for filet in files:
            print filet
            mat=sio.loadmat(filet)
            wave=mat['wavefunction'][0]
            J=mat['J']
            L=mat['L']
            n=mat['n']
            xmax=mat['xmax'][0][0]
            xmin=mat['xmin'][0][0]
            xstep=mat['xstep'][0][0]
            energy=mat['energy'][0][0]
            name=filet.replace('.mat','.txt')
            name=name.replace('rb','Rb')
            x=np.linspace(xmin, xmax, num=len(wave), endpoint=False)
            Data=np.transpose([x,wave])
            np.savetxt(name,Data)
            os.remove(filet)
            with open(name, "a") as f:
                    f.write(str(energy)+" "+str(xstep)+"n")
                    f.write(str(xmin)+" "+str(xmax))

and the format of the data file needed is :

    2.700000000000000000e+01 6.226655250941872093e-04
    2.700099997457605738e+01 6.232789496263042460e-04
    2.700199994915211121e+01 6.238928333406641843e-04
    2.700299992372816860e+01 6.245071764542571872e-04
    2.700399989830422243e+01 6.251219791839867897e-04
    2.700499987288027981e+01 6.257372417466700075e-04
    2.700599984745633364e+01 6.263529643590372287e-04

If you need more information, feel free to ask! Thanks in advance.