Zeuthen chicane example script

[jamesclarke22]

Hi All,

If you don't mind could you please share an input script for Zeuthen chicane example with Ocelot, so that I can understand how it is configured within Ocelot.

Thank you very much.
James

[st-walker]

Can you please share your initial attempt at implementing the chicane so that we can help you.

[jamesclarke22]

Hi @st-walker,

here is the minimal script

tws0 = Twiss()

#total beam charge
bunch_charge = 1.0e-9

# reference energy
bunch_energy = 5.0

# energy spread
sigma_p = 4.0e-5  # not sure if it is correct or not

#energy chirp
chirp = 0.0072    # not sure if it is correct or not

# pulse length
sigma_tau = 0.200e-3

# normalized emittances
emit_nor_x = 1.0e-6
emit_nor_y = 1.0e-6

# now convert to geometrical emittance for ocelot
emit_geo_x = emit_nor_x / (bunch_energy / m_e_GeV)
emit_geo_y = emit_nor_y / (bunch_energy / m_e_GeV)

# beam twiss parameters
tws0.beta_x = 40
tws0.beta_y = 13
tws0.alpha_x = 2.6
tws0.alpha_y = 1.0

tws0.gamma_x = (1 + tws0.alpha_x**2)/tws0.beta_x
tws0.gamma_y = (1 + tws0.alpha_y**2)/tws0.beta_y

tws0.emit_x = emit_geo_x
tws0.emit_y = emit_geo_y

# number of particles
npart = 10000

# generate particle array
p_array_init = generate_parray(sigma_tau = sigma_tau, sigma_p = sigma_p, charge = bunch_charge,
                              chirp = chirp, tws = tws0, nparticles = npart, shape="gauss")




# Now, make Zeuthen chicane lattice

distance_12 =Drift(5.0)  # distance between magnet 1 & 2
distance_23 =Drift(1.0)  # distance between magnet 2 & 3
distance_34 =Drift(5.0)  # distance between magnet 3 & 4

angle0 = 2.77 *np.pi/180

b1 = SBend(l=0.5, angle=angle0, e2=angle0, eid='B1')
b2 = SBend(l=0.5, angle=-angle0, e1=-angle0, eid='B2')
b3 = SBend(l=0.5, angle=-angle0, e2=-angle0, eid='B3')
b4 = SBend(l=0.5, angle=angle0, e1=angle0, eid='B4')

zeuthen_chicane = (b1, distance_12, b2, distance_23, b3, distance_34, b4)

[jamesclarke22]

Hi @st-walker,

please could you give me suggestions.

[st-walker]

1. Chicane outer drifts are wrong, you are mixing projected lengths and path lengths. should be factor of 1/cos(angle) longer.

2. You forgot the post chicane drift.

3. It's not on the website but you should have a pre chicane drift if you want to track with CSR because otherwise your transient field effect will be wrong (CSR effect starts from before the bend). This would then mean you need to recalculate your transverse optics if you start the beam further back.

This stuff:

# energy spread
sigma_p = 4.0e-5  # not sure if it is correct or not

#energy chirp
chirp = 0.0072    # not sure if it is correct or not

The website says on this line of the beam parameters table:

incoherent rms energy spread (DE)u-rms 10 keV

Incoherent energy spread is 10keV. So you need to set sigma_p = 10 keV / bunch_energy. is that what 4e-5 is? I didn't check

I think this is correct:

linear energy-z correlation a +36.0 m-1

in the generate_parray docstring then you can see that chirp is dimensionless, it's just the correlation. So I guess you need to multiply it by sigma_tau to get what you want (looking at the code). I assume this is what 0.0072 actually is.

The rest of what you did isn't obviously wrong, but I can't guarantee it's correct. Ultimately you need to read the code I am afraid to say and make plots to determine whether it's correct or not.

[jamesclarke22]

Hi @st-walker
Thank you for the suggestions. These are helpful. Only thing I am still not able to understand is: Uncorrelated relative energy spread before compression (DE/E0)u-rms = 4.0e-5. But if I do sigma_p = 10 keV / bunch_energy then it will give me sigma_p = 0.2e-5, which is different from (DE/E0)u-rms = 4.0e-5.

Do you have any suggestion for setting correct sigma_p ?

[st-walker]

I am not sure I understand where you are getting 4.0e-5 from. I can't see it on the website. I'm using the values from https://www.desy.de/csr/csr_workshop_2002/csr_workshop_2002_index.html

[jamesclarke22]

Hi @st-walker
the number 4.0e-5 I took from Desy CSR benchmarking