Slide 1 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Simulation comparison / tools / issues Henry Nebrensky Brunel University There are two kinds of fool. One says, 'This is old, and therefore good.' And one says, 'This is new, and therefore better.' —Dean Inge

Slide 2 MICE Beamline Design and Commissioning Review 16 th Nov 2007 MICE Beamline Simulation We are using two sets of code: PSI Graphic TURTLE and TRANSPORT (1 st, 2 nd and 3 rd order matrix ray tracing and beam propagation) –Fast (min/Mpion), extensive history including use in other pion-muon decay channels Tom Roberts’ G4beamline (Geant4 based) –New, has comprehensive scattering and trajectory physics, but slow (hours/Mpion)

Slide 3 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Simulation differences For a beamline expected to result in a 6π emittance beam, Turtle beam was found to be 7.1π mm rad [1] G4beamline (G4BL) gave 11.7π mm rad [2, 3] Also significant differences in beam profile… /CM14-7.1pi-200-TJR.ppthttp:// 31/CM14-7.1pi-200-TJR.ppt /CM14_200MeV_c_summary.pdfhttp:// 02/CM14_200MeV_c_summary.pdf

Slide 4 MICE Beamline Design and Commissioning Review 16 th Nov 2007 MICE Beam Widths 1. Changing Turtle options and interpretation of its output gives a wide range of beam sizes (none matching G4BL) cm m

Slide 5 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Common 30 mrad beam after B Identical input beams, scattering elements removed

Slide 6 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Common 10 mrad beam after B Stopping down the beam removes differences

Slide 7 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Common 30 mrad beam after B2 (rev. pol.) 1. N.B.Graph upside-down as quad polarities reversed (not the point… )

Slide 8 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Turtle only in 1 st order (rev. pol.) 1. Dropping higher-order term removes differences

Slide 9 MICE Beamline Design and Commissioning Review 16 th Nov 2007 MICE Beamline Simulation Is TURTLE correct? Is G4beamline correct? Are both codes modelling the same lattice? ( Does the model match what’s being built? )

Slide 10 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Is G4beamline correct? (1) A number of bugs found, including significant issues with fringe fields in both dipoles and quads[1]. 1. Tom Roberts: “G4beamline Fringe Field Study” 27 th Sept Comparison of generic dipole fringe fields with field map [1]

Slide 11 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Is G4beamline correct? (2) Also correctly imports field maps. Use version 1.14pre or later. 1. Tom Roberts: “G4beamline Fringe Field Study” 27 th Sept Comparison of generic quad fringe field with Q35 field map[1]

Slide 12 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Are input decks equivalent? Worked through by hand, believe they are now for Decay Solenoid and Transport Channel. Issues found in: Dipole fringe fields Quad apertures and fringe fields Scattering Reference particle trajectory Aligned cuts taken, and emittance calculations (converged on ecalc9 ) Add reference G4BL decks to repository

Slide 13 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Is TURTLE correct? Have reverse-engineered several features! :( Turtle incorporates fringe fields by parameterising them as dimensionless integrals. Dipole integrals (“K1”, “K2”) inconsistently documented – have decided on appropriate values [1] Quad integrals – use example values when needed. Real quads will have mirror plates so can treat as no fringe fields.(Code to calculate is on PSI site, haven’t tried it yet) 1.

Slide 14 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Is TURTLE correct - single muon tracks Have sent single particles through a single MICE quad (Q4) with correct aperture, field strength, muon momentum etc. But: no fringe fields, and no air. Have compared Turtle running in 1 st and 3 rd order with 1 st order equations implemented in Excel. Tested a series of cases, and looked at difference in x’ after the quad. The muon trajectories are confined to either the focussing or defocussing plane. For each case, the geometry is illustrated by just the 3 rd order Turtle results in the focussing plane, followed by a graph showing the difference in x’ using the Excel 1 st order model as the reference. 1.

Slide 15 MICE Beamline Design and Commissioning Review 16 th Nov 2007

Slide 16 MICE Beamline Design and Commissioning Review 16 th Nov 2007

Slide 17 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Converging group, x’ 0 to 432 mrad

Slide 18 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Outermost muon not scraped in 3 rd order Turtle

Slide 19 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Single muon tracks The two 1 st order models give near-identical results; confirms 1 st order Turtle is arithmetically correct. With 3 rd order, can get ~ 2% difference in x’ per quad; compounds down beamline. Gets worse for large-amplitude particles. Is the contribution from the extra term in 3 rd order Turtle correct? Will check. 1.

Slide 20 MICE Beamline Design and Commissioning Review 16 th Nov 2007 (Is the model right?) Lattice checked as part of the inter-code comparison. Kevin Tilley has added a set of “patches” to the TURTLE to overcome its limited handling of scattering, esp. from the air along the beamline. 1.

Slide 21 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Current beam size comparison Agreement in horizontal but still difference in the vertical plane

Slide 22 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Conclusions The latest comparison for “6π” beamline: TURTLE gives 8.4π mm rad beam G4BL gives 8.8π mm rad beam (as seen in Kevin’s talk) (Turtle: FOR035_1s_Ptotcut_noffs.DAT) G4BL: NoFF, 10%Cut)

Slide 23 MICE Beamline Design and Commissioning Review 16 th Nov 2007 Further Work We have identified a need to check 3 rd order Turtle; implement 3 rd Order in Excel to compare ( not trivial - see right ) G4BL comparison? Move ref. deck repository into CVS. D.L. Smith: “Focusing Properties of Electric and Magnetic Quadrupole Lenses” NIM 79 pp (1970)