# Time shift and time structure in phase space after particle-matter interaction

### Summary

The longitudinal phase space exhibits a time structure and the time needed to penetrate the material differs significantly depending on the seed and number of cores used to compute. This can be seen in the following plot showing histograms for the time of arrival at a monitor after a degrader:

### Steps to reproduce

Run the Degrader-1 regression test and plot a histogram of the time of arrival at the monitor M1. Use different seeds and number of cores to run the test.

###
*bug* behavior?

What is the current The phase space exhibits a time structure that corresponds to the length of the time step and the mean time of arrival differs significantly for different setups. This size of this time shift cannot be explained by the stochastic nature of the particle-matter interaction.

###
*correct* behavior?

What is the expected There shouldn't be a regular time structure and the difference of mean time of arrival for different setups should be very small.

### Relevant logs and/or screenshots

See above.