ramping with sextupoles

[Samira.kasaei]

Dear Michael,

I am using ramping example for my lattice. I wanna to consider the effect of sextupoles to correct the chromaticity. Without sextupoles the particles dont lose while with sextupoles, 70% of the particles lost. I used KSEXT for sextuploes. Could you please take a look at my files?

Many thanks in advance
samira

[michael_borland]

Samira,

You are using default_order=1 on &run_setup, which means all matrix computations are done to first order. Hence, the chromaticity appears to be zero, but then you track with KQUAD and KSEXT elements, which have momentum dependence to all orders. You can use a matrix-based dipole magnet with ORDER=1 if you know that this is a good approximation. You can then leave default_order=2 so that matrix computations for quadrupoles and sextupoles capture the chromatic effects.

Also, your KQUAD and KSEXT elements don't have values for N_SLICES, which means it defaults to 1. That's probably not enough. Try N_SLICES=5 and INTEGRATION_ORDER=6 to get a better model.

See the attachment for my changes to your files.

--Michael

[Samira.kasaei]

Dear Michael,

Many thanks for your reply. It works now.
If I wanted to take in to account the effect of eddy current during energy ramping, Is Elegant able to calculate the effect? If yes, how and If you can refer me to an example it is great.

Many thanks in advance,
Samira

[michael_borland]

Samira,

elegant can't compute the variation of the sextupole due to eddy currents. It depends on many details, such as the vacuum chamber shape and the construction of the magnet. Google is the best place to start.

--Michael

[Samira.kasaei]

Dear Michael,

Many thanks for your reply.
May I ask you about order in definition of dipole? If I use order =1 for dipole with and without sextupole I don't lose particles. In which case are we using order =2?

Best regards,
Samira

[michael_borland]

Samira,

The reason you can get away with turning off the sextupoles is that the energy spread and uncorrected linear chromaticities are fairly small and there is no significant nonlinear chromaticity. Hence, the particles tunes don't overlap any dangerous resonances, so nothing is lost.

--Michael

[Samira.kasaei]

Dear Michael,

Many thanks for your reply. I calculated the ramp for 1% energy spread. Without sextupoles I lost 23.4% of particles.Then I applied chromaticity correction to zero and I repeated the calculation. However I lost the same particles again. I was wondering if you can take a look to my files.

Best regards,
Samira

[michael_borland]

Samira,

I modified your file to ensure that the chromaticity correction converges. Convergence is slow with three families.

I did tracking and didn't see losses up to 20,000 turns. If you still see losses, I suggest looking at the data turn-by-turn to ensure that the beam is inside the rf bucket. I used an rf voltage pedestal of 0.5 MV.

-Michael

[Samira.kasaei]

Dear Michael,

Many thanks for reply. I changed my lattice. By Ramping at natural chromaticity, 165 particles lost.
After setting K2 parameters in dipole and in local sextupoles to reach +4 chromaticity, again I repeated ramping but in this case all of the particles are lost. I tried with zero and +1 chromaticities and I got the same results. I was wondering what is wrong!
Here are my files if you can take a look. Many thanks in advance for your support.

Best regards,
Samira