Large discrepancy between ECNX & ENX

[Zamank]

Hi All,

Pretty curious over some odd data. I basically have some accelerating structures and a chicane (standard 4-dipole), despite the fact that the dispersion is cancelling at the end of the chicane the ENX>>ECNX.

Any ideas of what could be causing the discrepancy between the ecnx and enx?

[michael_borland]

Sorry for the delayed reply. I was on vacation.

The problem is that although the dispersion is nominally cancelled, CSR kicks inside the chicane introduce correlations between x and delta. This probably originates in the last two dipoles, where the bunch is short. See attached plots.

--Michael

[Zamank]

Hi Michael,

So, the ECNX over compensates and subtracts off these CSR-induced correlations? Am I correct in stating that in this case ENX would be a more accurate depiction of the transverse emittance?

Thanks

[michael_borland]

Yes, that's right. ECNX is just the ideal value you'd get if you somehow managed to remove all the correlations.

--Michael