Particle distribution generated with bunched_beam using use_moments_output_values

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tiansk
Posts: 39
Joined: 16 Mar 2012, 22:01

Particle distribution generated with bunched_beam using use_moments_output_values

Post by tiansk » 29 Jun 2021, 08:18

Hi Michael,

As shown in the attached example, I want to use the moments_output file to generate the particle distribution by set the parameter use_moments_output_values=1 in bunched_beam. I first checked the emittance of the generated particles by using sddsanalyzebeam command, the results is ex/ey=3.387026652738970e-09/4.106160920677630e-11,while the e1 & e2 value in mom file is 2.633363e-09/3.048417e-11.The emittance values are not exactly equal, but close. When I further check the phase space distribution,the x-phase space is not Gaussian,is there something wrong?

Best,

Tiansk
Attachments
makeBunch.zip
(6.19 MiB) Downloaded 102 times
y_phase_space.jpg
x_phase_space.jpg

tiansk
Posts: 39
Joined: 16 Mar 2012, 22:01

Re: Particle distribution generated with bunched_beam using use_moments_output_values

Post by tiansk » 02 Jul 2021, 02:48

Hi Michael,
I think I've found the reason for the strange distribution of particles in the x direction. I want to generate three sigma cutoff Gaussian particle distribution, I should set the distribution_cutoff parameter, not the enforce_rms_values parameter. When I set distribution_cutoff[0] = 3*3,the particle distribution is as shown in the attachment.

But the sddsanalyzebeam command gives the ex/ey parameters still doesn't match the e1/e2 parameters in mom file.

Best,

Tiansk
Attachments
x_phase_space2.jpg
y_phase_space2.jpg

michael_borland
Posts: 1797
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Particle distribution generated with bunched_beam using use_moments_output_values

Post by michael_borland » 15 Jul 2021, 14:11

Tiansk,

The e1 and e2 parameters in the output file from moments_output are the emittances of the two independent modes. These won't necessarily correspond to the projected emittances reported by WATCH or sddsanalyzebeam if there are x-y tilts present. To get agreement, you'll need to rotate the beam into the frame where the correlations are absent.

--Michael

duanz
Posts: 49
Joined: 30 May 2009, 01:50

Re: Particle distribution generated with bunched_beam using use_moments_output_values

Post by duanz » 18 Jul 2021, 19:30

Hi Michael,

Then I think it makes sense if you could implement the calculation of the eigen-emittances into sddsanalyzebeam, since the Sigma_matrix is already there.

I do understand it might take more efforts / and slow down the simulations (if this information is not relevant) if also outputing the eigen-emittances in the WATCH element in the "parameter"-mode.

For interested users, they could postprocess the output of a WATCH element in the "coordinate"-mode using sddsanalyzebeam if this capabillity is implemented.

Thanks!

Zhe Duan

michael_borland
Posts: 1797
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: Particle distribution generated with bunched_beam using use_moments_output_values

Post by michael_borland » 20 Jul 2021, 14:29

Zhe,

Yes, I agree that would be a nice feature. I'll add it to the to-do list.

--Michael

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