SixTrack: Minor bug fixes and pencil beam R. Bruce

Output of single diffractive events Inelastic interactions printed out on FLUKA_impacts.dat for use by FLUKA team In IR7, FLUKA team re-tracks all single diffractive events to correct for approximations in the K2 cross section Also single diffractive events needed in FLUKA_impacts.dat In present release version checked out from svn, this is NOT the case (discovered during the review preparations) R. Bruce, Interaction type

Output of single diffractive events Reason: output inside if-statement. Only inelastic written out First, coordinate transformation. Then writeout, then set to mm …. R. Bruce,

Fix of output of single diffractive events Include also single diffractive in if-statement (nabs=4) But apply coordinate transformation NOT to x as in old code, as we need to keep tracking the x for single diffractive. Instead, set x_flk=x and then transform x_flk. R. Bruce,

Fix of output of single diffractive events Apply change to 99.99mm only for particles with nabs=1 All changes enclosed within tags /* start RB fix */ and /* end RB fix */ Benchmark: ran SixTrack for 256 particles with IDENTICAL random seeds with old and new code. All files and output numbers are identical except additional lines in FLUKA_impacts with additional lines for single diffractive. Fix seems to work R. Bruce,

Minor changes to error modeling In fort.3, one can set the range in s to which errors on collimators should be applied. In release version this does not work (errors applied everywhere) After some serious debugging, error found Fix: Including TCRYO R. Bruce,

Pencil beam Can choose starting conditions between different types of annular phase space distribution (standard halo) and pencil beams Example loss maps for 3.5 TeV, b*=1.5m, hor halo B1. Identical inputs apart from starting conditions R. Bruce, Pencil beam Halo Inefficiency the same within 5% higher TCT losses in with pencil beam

Pencil beam TCT leakage per plane and beam Pencil beam Halo Pencil beam seems to overestimate losses on vertical TCTs. Reason presently unknown

Pencil beam routine Tried to look in detail on pencil beam routine Minor inconsistencies found Tilt angle applied at TCP on first turn and not later Distribution perpendicular to collimation plane not mathced (all angles set to 0) Correct angle of pencil beam, accounting for beam divergence Other differences: With the halo deformation over several turns by non-linearities, halo routine tends to load one TCP jaw more than the other. Pencil beam splits the hits equally between jaws. Detailed explanation of discrepancies still to be understood. Halo seems to better reproduce measurements. Agreement good if FLUKA factor accounted for (see IPAC).

Ideas for improvement and pending issues Observed unnaturally high amount of inelastic inetractions at the end of TCP. Probably not critical, but should be understood. Pointed out by FLUKA team Store history of each particle for debugging and easier understan- ding of loss maps (already done by Daniele?) When using random seed = 0, one could write out the actual used seed to a file so that the run can be repeated afterwards for debugging Inelastic interactions on TCP