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Hi Michael,

I am trying to use sextupoles for reducing emittance growth in the beam line after the dipole. Since there is dispersion (in x), I expect that sextupoles just affect the emittance growth in x. But both emittances decrease using these sextupoles while there is dispersion just in x not in y plane. In y plane without dispersion these sextupoles should work like quadupole that makes emittance growth.

I have attached the lattice and tracking files.

Thank you in advance,
Farzad

Farzad,

Theoretically, even for a thin-lens sextupole, there is a small change in the vertical divergence in going through a sextupole if there is horizontal dispersion and energy spread. So the emittance change you see is correct.

You can try it with a KSEXT element (which is a completely different implementation) and you'll get the same result.

--Michael