Elegant users forum

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

Thank you in advance for your precius help
Marcello

Marcello,

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

--Michael

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