atplot of a single cell, without cavity

[simoneliuzzo]

The command atplot is returning an error (missing cavity) when producing a plot of a single cell extracted from a lattice with radiation on. The error is correct as the lattice is not complete and in fact it does not only miss a cavity, but all the other cells to close the lattice.

Nevertheless, for a single cell, 4D may be assumed implicitly?

In general, when working with an arbitrary lattice (4d or 6d), I must replace the usual friendly call to atplot(ARC) with atplot(atradoff(ARC)) to make sure the plot will appear.

[lfarv]

Hi @simoneliuzzo.
atplot is just displaying the result of atlinopt6. So you question should rather be addressed to atlinopt6.

atlinopt6 (in "closed ring" mode, not in "transfer line mode") only needs a closed solution (exactly as atlinopt). It has no notion of arc, cell, ring… and it does not care. It works perfectly with a lattice without any bending magnet, which cannot be neither an arc nor a full ring. The only condition to get β values is to find a closed solution, either in 4D or in 6D.

So it's perfectly valid to work in 6D on a single superperiod. It's even the most efficient solution for studying periodic rings: same result with less computation.

Your problem probably comes when giving a cell with radiation but no cavity. Then there is obviously no closed solution ! Either you add a cavity, or you remove the radiation, but it's up to you to decide, AT cannot guess what you want.

Notes:

• even trying to use the old atlinopt with radiation (which is strictly forbidden) will never give a solution in these conditions. So no regret, it never worked !
• using atplot(atradoff(ring)) is not a bad solution: β-functions don't depend on longitudinal motion. atplot now accepts 6D lattices for your convenience: it works with any arbitrary stable lattice, 4D or 6D. But 6D has strictly no added value for the plot.