Longitudinal aperture element

[SebastienJoly]

Hello,
I would be interested by a longitudinal aperture ($\phi$, $\delta$) element. I am currently running simulations with a lattice exhibiting $\alpha_0 \approx \alpha_1$ thus leading to the appearance of a second row of stable RF buckets for negative $\delta$. When I try to compute the momentum acceptance, particles outside the synchronous particle RF bucket can sometimes be trapped between both buckets' rows yielding an inflated momentum acceptance. To overcome this issue, it is still possible to track the particles for a sufficiently large number of turns to ensure they are lost. However, momentum acceptance calculations below a few hours of computations would be welcome.
Therefore, would it be possible to tweak the transverse aperture element and transpose it to the longitudinal plane? This way, we can force particles outside the main RF bucket to be considered lost.