Elegant users forum

Dear Mr. Michael Borland,
I was wondering if you could share with me the technical note AOP-TN-2013-076 from 2013 named
"Surprising result for emittance partioning from coupling".
There is in this presentation:
https://www.aps.anl.gov/files/APS-Uploa ... -10-27.pdf
a formula in slide 12 that is not to be found (explicitly) in R. Lindberg, AOP-TN-2014-020.
Kind regards,
Cristopher Cortés

Cristopher,

ANL policy doesn't allow me to post technical notes outside of the lab.

The "surprising result" was really just something I didn't know. Namely, when we have combined-function magnets, the emittance partitioning is not ex=e0/(1+k), ey=k*ex, but rather ex=e0/(1+k*Jy/Jx), ey=k*ex, where Jx and Jy are the horizontal and vertical damping partition numbers. In an isomagnetic ring, Jx=Jy=1, so we recover the simple result. In a ring with combined-function magnets, Jx is not 1.

For example, in the APS upgrade lattice, we have e0=42pm, Jx=2.25, and Jy=1. With k=1 (full coupling), we get ex=ey=28.9pm. The simpler formula gives an incorrect result, namely, ex=ey=21pm.

--Michael

Dear Michael,
Thank you very much.
Cheers,
Cristopher