pepper-pot emittance measurement

[QJohn]

The reason to use the RCOL or ECOL element is that it allows easily separating the beamlets. With the PEPPERPOT element, you have to separate the beamlets yourself in postprocessing. In a real experiment with a pepper-pot plate, that's what you'll have to do, but for developing the basic method, it is easier to do one beamlet at a time.

--Michael

Do you mean that with the RCOL or ECOL element, it processed a single beamlet at a time and the final emittance exEst and eyEst contained all the beamlets' contribution? Thank you very much!

[michael_borland]

Yes, that's right.

--Michael

[QJohn]

Yes, that's right.

--Michael

Thank you, Michael. How can I upload files and images in the subjects?

[michael_borland]

Thank you, Michael. How can I upload files and images in the subjects?

Click on the attachments tab below the composition window, then use the "Add files" button.

See attachment.

--Michael

[QJohn]

Very likely the problem is that you haven't adjusted the quadrupoles to give the condition alphax=alphay=0 at the position of the pepper pot plate. Without this, the analysis is more complex than what my simple example supports. In fact, I think you'd need to observe the beam at two locations downstream of the pepper pot plate to obtain the emittance in that case.

--Michael

Than you Michael, I now have three quuestions,
1. I can't do parallel computation,the erros as follows:

1.PNG (9.91 KiB) Viewed 5512 times

2.When I do'nt use the parallel computation, I follow your advice and add two parameters alphax=0 and alphay=0 in .ele file, meanwhile, I output the results when the electron beam reached the pepperpot plate. But I also get the following erros:

3.PNG (5.91 KiB) Viewed 5512 times

the output files I before.out and before.sig which I added in the .lte file are too large , about 14GB. The accessory is the elegant files. Can you help me to optimize it? Than you very much!

[QJohn]

Very likely the problem is that you haven't adjusted the quadrupoles to give the condition alphax=alphay=0 at the position of the pepper pot plate. Without this, the analysis is more complex than what my simple example supports. In fact, I think you'd need to observe the beam at two locations downstream of the pepper pot plate to obtain the emittance in that case.

--Michael

Than you Michael, I now have three quuestions,
1. I can't do parallel computation,the erros as follows:

The attachment 1.PNG is no longer available

2.When I do'nt use the parallel computation, I follow your advice and add two parameters alphax=0 and alphay=0 in .ele file, meanwhile, I output the results when the electron beam reached the pepperpot plate. But I also get the following erros:

The attachment 2.PNG is no longer available

pepperpot.zip

(154 Bytes) Downloaded 323 times

the output files I before.out and before.sig which I added in the .lte file are too large , about 14GB. The accessory is the elegant files. Can you help me to optimize it? Than you very much!

Sorry, Michael ,I forgot to upload the accessory,

pepperpot.zip

(154 Bytes) Downloaded 323 times

[michael_borland]

The zip file is empty.

--Michael

[QJohn]

The zip file is empty.

--Michael

Sorry, Michael, please check out the accesory again.

pepperpot.zip

(1.52 KiB) Downloaded 334 times

[QJohn]

The zip file is empty.

--Michael

Sorry, Michael, please check out the accesory again.

Hi, Michael, I don't know weather you can see my questoins which I pointed out before by pictures . I now repeat my questions again:
1. I can't do parallel computation,the erros as follows:

1.PNG (9.91 KiB) Viewed 5511 times

2.When I do'nt use the parallel computation, I follow your advice and add two parameters alphax=0 and alphay=0 in .ele file, meanwhile, I output the results when the electron beam reached the pepperpot plate. But I also get the following erros:

3.PNG (5.91 KiB) Viewed 5511 times

the output files I before.out and before.sig which I added in the .lte file are too large , about 14GB. Can you help me to optimize it? Than you very much!

[michael_borland]

The root of all the problems is that the beam is not upright in phase space at the entrance to the RCOL element. This causes the computations to fail because it violates one of the assumptions of the pepper pot method. When the calculation produces an invalid value (square root of a negative number) that subsequently generates the error about too few items on the stack.

You put alpha_x=0 and alpha_y=0 in the &bunched_beam command, but that controls the beam parameters at the start of the simulation, not at the entrance to the pepper pot plate. Look at the before.out file and you'll see that the beam is a tilted stripe in (x, x') and (y, y') phase space. The pepper pot method won't work in this case. If you tune the two quadrupoles to give the required conditions alpha_x=0 and alpha_y=0 at the entrance to the RCOL element, it should all work fine.

As for before.out and before.sig being too large to upload: you inserted two WATCH elements (W1 and W2) into the lattice. In the default mode, they dump the coordinates of all the particles that they see into the named files (before.out and before.sig, respectively). I suspect you don't want that, particularly since the two files will contain exactly the same data. Consult the manual to see proper use of the WATCH element.

--Michael