"beamline unstable" problem

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Marcello
Posts: 19
Joined: 28 Jan 2015, 10:05

"beamline unstable" problem

Post by Marcello » 27 Feb 2015, 12:18

Dear Michael,

I'm simulating the focusing of an ultra-short electron bunch for plasma injection, in LWFA .
The beam emittance in really low (0.2e-6 m, for 15pC of charge). It's a cylindrical beam and it's envelope is 1 mm and Ss = 4.2e-6 m.

The tracking of this beam, by using ASTRA, doesn't give any problem. Now I'm trying to optimize the focusing channel, for the plasma injection, by using a triplet; Elegant replies "warning: beamline unstable for y plane--can't match beta functions." (Using only a drift the error is "Unable to compute dispersion: unstable").
The problem is that with this error it's not possible to perform the optimization that I'm trying to do.
If you belive that the problem lies in the bunch
in.sdds
(469.09 KiB) Downloaded 245 times


Thank you in advance for your precius help
Marcello

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: "beamline unstable" problem

Post by michael_borland » 27 Feb 2015, 13:38

Marcello,

This will only happen if you have matched=1 (the default) in &twiss_output. Try setting matched=0.

--Michael

Faissal
Posts: 16
Joined: 11 Jan 2017, 14:53
Location: Diamond Light Source (UK)

Re: "beamline unstable" problem

Post by Faissal » 14 Feb 2018, 11:04

Dear Michael,

The solution suggested makes sense since it's a linac so putting matched=0 removes the issue. But sometimes the above warning message can also occurs in situations when a ring is simulated. It does not necessarily prevent the optimization to go on, but does this message mean that something is wrong in the lattice definition? For a ring we used matched=1.

regards,

- Faissal

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