Extracting Twiss parameters

[dmargarone]

Hi,

I described a particle array as follows:

p_array_init = generate_parray(sigma_x=1.0e-3, sigma_tau=0.5e-3,
                               sigma_px=7e-5, energy=0.1, nparticles=20000, charge=1e-09)

How can I get the Twiss parameter of the electron beam corresponding to this "p_array_init".

Thank you.
Daniele

[st-walker]

get_envelope

[dmargarone]

@st-walker ,

Thank you.

Daniele

[dmargarone]

Hi @st-walker , I have one confusion about the emittance of the electron beam that I get from the "get_envelope" and what I saw from "show_e_beam".

p_array_init = generate_parray(sigma_x=100.0e-6, sigma_y=100.0e-6, sigma_tau=100.0e-6,
                               sigma_px=7e-5, chirp=0.0002, energy=Eb,
                               nparticles=20000, charge=1e-09)


# get twiss parameters of the electron beam
Twiss = get_envelope(p_array_init)

print("")
print("Twiss parameters corresponding to p_array_init")
print("")
print(Twiss)

show_e_beam(p_array_init, figsize=(9,6))

show_e_beam gives emit_x = 1.36 mm. mrad and emit_y = 1.37 mm. mrad, where as Twiss parameters from get_envelope gives emit_x = 6.949964803224176e-09 and emit_y = 6.982866393378305e-09.

Why there is so big difference in show_e_beam and get_envelope values.

[st-walker]

can u show plot?

[dmargarone]

@st-walker , yes here it is attached.

[st-walker]

perhaps you are comparing two different quantities: geometric emittance and normalised emittance. in output of get_envelope there is emit_x and emit_xn. I think the plot will probably be emit_xn and emit_yn, which is a factor of relativistic gamma * beta greater than geometric emittance.

[dmargarone]

And the electron beam energy in "p_array_init" is Eb = 0.1