SixTrack : Minor bug fixes and pencil beam R . Bruce

1. SixTrack: • Minor bug fixes and pencil beam • R. Bruce

2. 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) Interaction type

3. Output of single diffractive events • Reason: output inside if-statement. Only inelastic written out • First, coordinate transformation. Then writeout, then set to 99.99 mm • ….

4. 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.

5. 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

6. 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

7. 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 Halo Pencil beam higher TCT losses in with pencil beam Inefficiency the same within 5%

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

9. 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).

10. 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 fordebugging 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