### Touschek lifetime and +/- momentum aperture

Posted:

**04 Jan 2013, 10:07**At ESRF we are doing some lattice studies for our current and upgraded storage rings, using Elegant to compute the momentum aperture and resulting Touschek lifetime.

Elegant computes the positive and negative momentum aperture to be used in the lifetime calculation. The corresponding scattering rates should then be added to get the total scattering rate (1/tau = 1/tau_p + 1/tau_n).

However, looking at the touschekLifetime C code, it seems that the minimum of the momentum aperture is used.

We have cases with big enough asymmetry between delta_p and delta_n that this difference in evaluation of lifetime has significant impact.

Did we read the source code correctly?

Are we right in thinking the lifetime should be computed including the positive and negative terms separately?

Nicola Carmignani

Boaz Nash

Elegant computes the positive and negative momentum aperture to be used in the lifetime calculation. The corresponding scattering rates should then be added to get the total scattering rate (1/tau = 1/tau_p + 1/tau_n).

However, looking at the touschekLifetime C code, it seems that the minimum of the momentum aperture is used.

We have cases with big enough asymmetry between delta_p and delta_n that this difference in evaluation of lifetime has significant impact.

Did we read the source code correctly?

Are we right in thinking the lifetime should be computed including the positive and negative terms separately?

Nicola Carmignani

Boaz Nash