beam size

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Samira.kasaei
Posts: 26
Joined: 15 Jun 2021, 13:38

beam size

Post by Samira.kasaei » 16 Apr 2023, 05:21

Hello Michael,

I tried to calculate beam size for my ring but variation of the beam size is not small along the ring. Could you please take a look to my files?

Thanks alot and best regards,
Samira
Attachments
chro.new
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nominal.ele
(817 Bytes) Downloaded 43 times
beam-size.png

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: beam size

Post by michael_borland » 02 Jun 2023, 10:25

Samira,

You need to ensure that you generate a matched beam to start. You have

Code: Select all

&bunched_beam
        n_particles_per_bunch = 1000,
        one_random_bunch=0,
        emit_x = 26e-9,
       emit_y = 26e-9,
        distribution_type[0] = 3*"gaussian",
        distribution_cutoff[0] = 3*3,
       ! symmetrize = 1,
        enforce_rms_values[0] = 1,1,1,
&end

&twiss_output
        filename = "%s.twi",
        final_values_only = 0
&end
The beam distribution has no defined beta functions, so some defaults will be used. What you want are the periodic beta functions from twiss_output. You can get the desired result by changing the order of twiss_output and bunched_beam, and adding the use_twiss_command_values=1 parameter to bunched_beam:

Code: Select all

&twiss_output
        filename = "%s.twi",
        final_values_only = 0
&end

&bunched_beam
        n_particles_per_bunch = 1000,
        one_random_bunch=0,
        emit_x = 26e-9,
       emit_y = 26e-9,
        distribution_type[0] = 3*"gaussian",
        distribution_cutoff[0] = 3*3,
       ! symmetrize = 1,
        enforce_rms_values[0] = 1,1,1,
        use_twiss_command_values = 1
&end
--Michael

Samira.kasaei
Posts: 26
Joined: 15 Jun 2021, 13:38

Re: beam size

Post by Samira.kasaei » 13 Jun 2023, 03:36

Dear Michael,

Now it is working. However when I add some skew quads in my lattice I got the same vertical beam size. What is wrong in your opinion?

Many thanks and best regards,
Samira

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: beam size

Post by michael_borland » 13 Jun 2023, 05:41

Samira,

Please post your files and I'll take a look.

--Michael

Samira.kasaei
Posts: 26
Joined: 15 Jun 2021, 13:38

Re: beam size

Post by Samira.kasaei » 18 Jun 2023, 04:18

Dear Michael,

Please find the attached.

Best regards,
Samira
Attachments
SQ.new
(4.22 KiB) Downloaded 36 times
nominal.ele
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michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: beam size

Post by michael_borland » 19 Jun 2023, 12:12

Samira,

I think the problem is partly that your skew quadrupoles are relatively weak. For example, if I multiply the skew strengths by 100, there's a clear effect on Sx and Sy in the .sig file.

Also, please note that &twiss_output does not give trustworthy results in the presence of strong coupling. You can use &coupled_twiss_output instead, as well as &moments_output.

--Michael

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