Elegant users forum

Hi All,

Have a sort of odd problem I ran into yesterday with ELEGANT. I wrote a script manually calculating the x-plane emittance of a beam at some watch point at the exit of a bunch compressor (BX24DEND.out). The issue comes from a significant discrepancy from my calculated emittance and the emittance that ELEGANT gives in the *.sig file. I am specifically looking at BX24DEND.out.

*.sig file gives for {ex,enx} = {1.752717e-08 ,6.803332e-06}

My manual calculation gives {ex,enx} = {4.244864e-08 ,1.661392e-05}

Was wondering if anyone has any idea as to why this is happening?

Relevant files are attached.

Thanks in advance!

The problem is that the beam has a non-zero x and x' centroid. These must be subtracted off before you compute the emittance. This is done for the emittance calculations report in the .sig file.

I modified your script to do this. Also, you can use the sddsanalyzebeam program.

--Michael

Here's the modified script.

--Michael

Hi Michael,

First thank for the reply; very helpful! Second, just to check my understanding:

The x,xp value of the *.out file are then measured with respect to the beam's centroid coordinates and not the on energy ideal particle?

Thanks

The coordinates in the output file are measured with respect to the reference axis of the accelerator, which would nominally be the location of the ideal on-momentum particle (assuming no correctors are powered, etc).

The version of the script that I sent does not modify the elegant output file, but simply prints the results after doing the computations with the average values removed.

--Michael