sddsemitproc including dispersion

[mjoyce]

Can you please tell me what I'm doing wrong here?
We suspect that there is dispersion leakage that is affecting the X emittance, so we wanted to try out the -includeDispersion option. Assuming sddsemitproc removes the dispersion contribution, I would expect a smaller emittance. Rather than larger.

One mistake may be the dipole that I included in the line for the -includeDispersion option. The matrix elements start_from that dipole. Should I start farther upstream?

If you're willing to look into this, email me for other relevant files. The forum wouldn't let me attach > 3

Thanks.
Michele Joyce
TJNAF

[michael_borland]

Michele,

Sorry for the delay in responding.

The -includeDispersion option is not reliable. It is actually disable in the most recent release. It attempts to determine the energy spread, but doesn't succeed well even in ideal cases. I think the problem is degenerate because the energy spread is a fixed quantity.

My suggestion is to subtract the dispersion contribution (in quadrature) from the beam sizes before. This requires that you know the energy spread already from a separate measurement.

--Michael

[michael_borland]

Michele,

It might work if you have significant dispersion at the location of one of the quadrupoles you vary.

--Michael

[mjoyce]

Thanks for the reply. We'll try the subtraction method.