Add more vacuum at z>40m

[michael-pitt]

Briefly, what does this PR introduce?

This RP will fill the hadron line downstream with a vacuum to allow faster simulation of ion fragments.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: This makes the simulation run faster in case of eA collisions in which ions (or ion fragments) are defined as stable particles and propagate downstream the Hadron beamline (x10 improvement).

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators: Presented at the FF WG meeting on May 14 https://indico.bnl.gov/event/23379/#15-forward-detectors-with-epic

Does this PR introduce breaking changes? What changes might users need to make to their code?

Besides the execution time, this PR should keep the results unchanged.

Does this PR change default behavior?

no

[michael-pitt]

Hi @wdconinc and @ajentsch

This update was communicated to the FF WG, and it is ready to be merged with the master. It should improve the execution time of the simulation for some processes involving particles that propagate downstream the hadronic beampipe

[veprbl]

There is a small extrusion from the world_volume, is that due to a rotation?

[veprbl]

Perhaps some rotated width is not accounted for.

[michael-pitt]

The introduced vacuum volume (tube) is placed between the last magnet (at z=40.74293743+4.4/2 meter) and the end of the physical volume (at z = 100 meters) and aligned with the last magnet rotation angle of -28.22mrad. The tube has radius of 4 times the B2 magnet radius (4*0.2 m). Hence at the end of the physical volume small part of the tube extends beyond the edge:

I'm open to suggestions. The easiest will be to shorten the length by 0.2*4*tan(-28.22*mrad) meters

[veprbl]

I'm open to suggestions. The easiest will be to shorten the length by 0.2x4xtan(-28.22mrad)

This is exactly what we want. Ideally, this is done in the compact xml file as an expression.

[simonge]

I'm open to suggestions. The easiest will be to shorten the length by 0.2x4xtan(-28.22mrad)

This is exactly what we want. Ideally, this is done in the compact xml file as an expression.

Would the CutTube approach (example present in the same file) be slightly better than shortening a tube.

[veprbl]

Looks fine