Simulation comparison / tools / issues

MICE Beamline Design and Commissioning Review16th Nov 2007 Slide 1

Simulation comparison / tools / issues

Henry NebrenskyBrunel 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


MICE Beamline Simulation

We are using two sets of code:

• PSI Graphic TURTLE and TRANSPORT (1st, 2nd and 3rd 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)


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…

1. http://www-kuno.phys.sci.osaka-u.ac.jp/~yoshida/MICE-CM14/talks/cm14_28_drumm_design.ppt2. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline

%20-%20optics/2006-05-31/CM14-7.1pi-200-TJR.ppt3. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline

%20-%20optics/2006-08-02/CM14_200MeV_c_summary.pdf


MICE Beam Widths

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-03-27/AllMuonsTTlvG4BL.xls

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0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000

Base Yrms

G4BL Yrms

BaseXrms

G4BL Xrms

FullFlg1 Y

FullFlg1 X

FullNoFg Y

FullNoFg X

Diffuserdownstream edge

Q9Q8Q7Q6Q5Q4B2 TOF0

Čerenkov

TOF1

Changing Turtle options and interpretation of its output gives

a wide range of beam sizes (none matching G4BL)

cm

m


Common 30 mrad beam after B2

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-06-07/TTlvG4BL_1stStage_JustNoDecData.xls

-20-19-18-17-16-15-14-13-12-11-10

-9-8-7-6-5-4-3-2-10123456789

1011121314151617181920

0 2 4 6 8 10 12 14 16

TTL NoDecIP + Qd Sli xrms(from 16599) TTL NoDecIP + Qd Sli yrms (from 16599) G4BL NoDec xms G4BL NoDec yrms

Q9Q8Q7Q6Q5Q4B2

Identical input beams, scattering elements removed


Common 10 mrad beam after B2

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-06-07/TTlvG4BL_1stStage_JustNoDecData.xls

-20-19-18-17-16-15-14-13-12-11-10

-9-8-7-6-5-4-3-2-10123456789

1011121314151617181920

0 2 4 6 8 10 12 14 16

G4BL NoDec xrms G4BL NoDec yrms TTL NoDecIP + Qd Sli xrms (from 16599) TTL NoDecIP + Qd Sli yrms (from 16599)

Q9Q8Q7Q6Q5Q4B2

Stopping down the beam removes differences


Common 30 mrad beam after B2 (rev. pol.)

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-07-24/TTlvG4BL_1stStage_JustNoDecData_postCM18_2.xls

-20-19-18-17-16-15-14-13-12-11-10

-9-8-7-6-5-4-3-2-10123456789

1011121314151617181920

0 2 4 6 8 10 12 14 16

G4BL NoDec xrms p_rev G4BL NoDec yrms p_rev TTL NoDec QdSli prev xrms (from 16599) TTL NoDec QdSli prev yrms (from 16599)

Q9Q8Q7Q6Q5Q4B2

N.B.Graph upside-down as quad polarities reversed

(not the point… )


Turtle only in 1st order (rev. pol.)

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-07-24/TTlvG4BL_1stStage_JustNoDecData_postCM18_2.xls

-20-19-18-17-16-15-14-13-12-11-10

-9-8-7-6-5-4-3-2-10123456789

1011121314151617181920

0 2 4 6 8 10 12 14 16

G4BL NoDec xrms p_rev G4BL NoDec yrms p_rev TTL NoDe QS pr 1st&2nd xrms (fr 16599) TTL NoDe QS pr 1st&2nd yrms (fr 16599)

Q9Q8Q7Q6Q5Q4B2

Dropping higher-order term removes differences


MICE Beamline Simulation

Is

TURTLE correct?

Is G4beamline

correct?Are both codes modelling the same lattice?

( Does the model match what’s being built? )


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” 27th Sept. 2007Comparison of generic dipole fringe fields

with field map [1]


Is G4beamline correct? (2)

Also correctly imports field maps.

Use version 1.14pre or later.

1. Tom Roberts: “G4beamline Fringe Field Study” 27th Sept. 2007

Comparison of generic quad fringe field with Q35 field map[1]


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 trajectoryAligned cuts taken, and emittance calculations

(converged on ecalc9 )Add reference G4BL decks to repository


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. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-01-16/K1K2Status2.ppt


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 1st and 3rd order with 1st 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 3rd order Turtle results in the focussing plane, followed by a graph showing the difference in x’ using the Excel 1st order model as the reference .

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-11-08/TTLvG4BL_Single_v2.pdf


Case B - Collimated axial beam

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0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

z [m]

x [c

m]


Case B - Difference in final x' as we go off axis

0.00%

0.20%

0.40%

0.60%

0.80%

1.00%

1.20%

1.40%

1.60%

1.80%

2.00%

0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000 18.000 20.000

Initial particle offset [cm]

Dif

f x'

/ x

'

TTL_1 vs Excel 1st Order Focusing TTL_3 vs Excel 1st Order Focusing

TTL_1 vs Excel 1st Order Defocusing TTL_3 vs Excel 1st Order Defocusing


Case H - fan-in

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0

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60

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100

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

z [m]

x [c

m]

Converging group, x’ 0 to 432 mrad


Difference in final x' as we increase x' at entry

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

4.00%

0 50 100 150 200 250 300 350 400

Initial x'

Dif

f x'

/ x

'

TTL_3 vs 1st (f) TTL_1 vs 1st (f)TTL_3 vs 1st (d) TTL_1 vs 1st (d)

Outermost muon not scraped in 3rd

order Turtle


Single muon tracks

The two 1st order models give near-identical results; confirms 1st order Turtle is arithmetically correct.

With 3rd 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 3rd order Turtle correct? Will check.

1. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-11-08/TTLvG4BL_Single_v2.pdf


(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. http://www.isis.rl.ac.uk/accelerator/MICE/Task%20Notes%20and%20Specifications/beamline%20-%20optics/2007-01-16/K1K2Status2.ppt


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TTL Y rms G4BL Yrms TJRModB2 TTL X rms G4BL Xrms TJRModB2

Diffuserdownstream edge

Q9Q8Q7Q6Q5Q4B2 TOF0

Čerenkov

TOF1

Current beam size comparison

Agreement in horizontal but still difference in the

vertical plane


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)


Further WorkWe have identified a need

to check 3rd order Turtle; implement 3rd 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.144-164 (1970)

Documents

Simulation comparison / tools / issues