Emittance again

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CCH
Posts: 16
Joined: 16 Apr 2010, 02:04

Emittance again

Post by CCH » 20 Jul 2010, 02:37

Mr Borland
I changed my lattice and get a new one with beta functions under 30 meters.The Ecny is good enough,But the Ecnx still changed a lot when I set the default_order=2 in run_setup.I can't understand why this happened.

-------------CCH
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michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
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Re: Emittance again

Post by michael_borland » 20 Jul 2010, 08:24

The reason is presumably that you have a large beam size in the second dipole, which has a very short bending radius rho. In second order, the equation of motion for x has a term x^2/rho. This term looks like a sextupole and is probably responsible for the emittance growth. Try reducing the beam size in the dipole magnets, or using longer dipoles to increase rho.

--Michael

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