How does ibsEmittance distributes emittance with coupling flag? In my MAD-X calculations I assumed that coupling between emittances works as
e0 = ex + ey; ex = e0(1+coupling); ey = ex*coupling. Here e0 is in my opinion should be ex0 from twissOutput, ex and ey coupled emittances. With my total emittance 73 pm for coupling=1 I would expect to get both coupled emittances ex=ey=73/2 pm, but I get somthing around 48 pm.
Coupling in ibsEmittance
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Coupling in ibsEmittance
Respectfully,
Mikhail A. Skamarokha.
Mikhail A. Skamarokha.
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Re: Coupling in ibsEmittance
Mikhail,
The formula you quote is incorrect when the horizontal damping partition number Jx is not 1. The correct formula is ex=ex0/(1+K*Jy/Jx), ey=K*ex.
For example, for APS-U we have ex0=44.3 pm and Jx=2.21. With K=1, we get ex=ey=30.5 pm
--Michael
The formula you quote is incorrect when the horizontal damping partition number Jx is not 1. The correct formula is ex=ex0/(1+K*Jy/Jx), ey=K*ex.
For example, for APS-U we have ex0=44.3 pm and Jx=2.21. With K=1, we get ex=ey=30.5 pm
--Michael
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Re: Coupling in ibsEmittance
But what about the sum rule of coupled emittances? If we were to use coupling as you discribed sum of coupled emittances won't be equal to uncoupled horizontal emittance from twissOutput for ideal lattice.
Respectfully,
Mikhail A. Skamarokha.
Mikhail A. Skamarokha.
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- Posts: 1951
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- Location: Argonne National Laboratory
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Re: Coupling in ibsEmittance
Mikhail,
The "sum rule" is only correct when Jx=1. If Jx>1, the sum of the emittances is always greater than the natural emittance.
--Michael
The "sum rule" is only correct when Jx=1. If Jx>1, the sum of the emittances is always greater than the natural emittance.
--Michael
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Re: Coupling in ibsEmittance
Understood. Thank you for a quick reply.
Respectfully,
Mikhail A. Skamarokha.
Mikhail A. Skamarokha.