Sextupole affects the beta function after an offset quad

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Jafarinia
Posts: 23
Joined: 02 Nov 2017, 12:25

Sextupole affects the beta function after an offset quad

Post by Jafarinia » 03 Aug 2020, 07:55

Hi Michael,

I designed a beam line with offset quads as bending magnets and I want to use sextuples to reduce emittance growth. I use center element to bring back the beam on the center after each quad, but sextupoles after the offset quads change the beta functions. It seems that to calculate the beta functions ELEGANT also take the effects of offset quads. I was wondering in this case how I can use sextupoles while keeping the beta functions as before.

Thank you in advance,
Farzad

michael_borland
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Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Sextupole affects the beta function after an offset quad

Post by michael_borland » 05 Aug 2020, 01:28

Farzad,

Which element are you using to model the offset quadrupoles? If they are really functioning as bending magnets, you should use the CCBEND element, which models straight dipoles with an optional transverse gradient. That way, elegant will place other elements (e.g., sextupoles) on the reference trajectory. Otherwise, the beam will go off center through the sextupoles, which results in a focusing term.

--Michael

Jafarinia
Posts: 23
Joined: 02 Nov 2017, 12:25

Re: Sextupole affects the beta function after an offset quad

Post by Jafarinia » 05 Aug 2020, 04:39

Hi Michael,

I was wondering why the center element doesn't bring the beam back on the center after quad?

Thanks,
Farzad

michael_borland
Posts: 1796
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Sextupole affects the beta function after an offset quad

Post by michael_borland » 05 Aug 2020, 09:54

Farzad,

In general, the CENTER element should be bringing the beam back on the reference trajectory. However, depending on how the options are set, it might not. If you can post an example of the problem, I'll look at it. However, using offset quadrupoles to model bending magnets is not right in a number of ways. Please try using CCBEND instead.

--Michael

Jafarinia
Posts: 23
Joined: 02 Nov 2017, 12:25

Re: Sextupole affects the beta function after an offset quad

Post by Jafarinia » 05 Aug 2020, 10:07

Hi Michael,

OK... I will try it with CCBEND.

Thanks,
Farzad

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