M. Hausmann for the FRIB Fragment Separator Collaboration FRIB Separator: Open Questions

 List of open question related to the FRIB fragment separator design Not necessarily complete and very likely biased Will start with where we are, then give questions/tasks  List of milestones for the design work  A collection of material for discussion Some old slides, some rather recent ones Unfortunately not a material for every single question/point Some slides that I ‘borrowed’ from others Preface/Outline M. Hausmann, 15 Sep 2010, Slide 2

 So far, we have A separator concept »Design goals (max. rigidity, acceptance, etc.) »Vertical momentum compressing achromat (preseparator) Small dispersion from target to wedge; large dispersion from wedge to achromatic focal plane; momentum compressing wedge in between »Plus two horizontal separator stages Each one: two dipoles stages with a wedge in between (like LISE spectrometer) A preliminary solution for the preseparator »Essentially corrected in 2 nd order at wedge and focal plane »Partially corrected in 3 rd order »All in a simplified model without fringe fields A general layout for the horizontal stages »Reusing the known (incl. fringe fields) A1900 magnets »Each stage largely corrected at focal plane, not so much at the wedge A ‘tool kit’ adequate to do the job »With some open questions/potential for further optimization Overview of where we are M. Hausmann, 15 Sep 2010, Slide 3

General Layout Vertical Preseparator plus Horizontal Stages 2 and 3, Slide 4 M. Hausmann, 15 Sep 2010

 General preseparator Rework entire ion optics with fringe fields »Fringe fields of A1900 magnets are a reasonable first guess, per A.Z. Effect of realistic target and wedge? Are the magnifications chosen so far the best choice? What are the best overall magnifications at the end of the preseparator? »Preseparator performance »Impact on following stages Misalignment sensitivity Preseparator Open Questions (1) M. Hausmann, 15 Sep 2010, Slide 5

 Front end (target to wedge) concept Beam dump at image between two counter bending dipoles »To catch primary beam as early as possible before it can damage magnets »Parallel beam in non-dispersive plane »Magnets directly following dump are dipole and dipole-like multipole, hence less susceptible to damage than quadrupoles Resolving powers of these dipoles add up at following image (wedge) Beam dump image uncorrected So far large magnification in non-dispersive plane  Open questions Alternative beam dump location possible?  Beam dump after 2 nd dipole → so far problems with dumping far off axis primary beams that don’t make it through 2 nd dipole Is the parallel beam in the non-dispersive plane at the dipole a good choice? How can we reduce the non-dispersive plane magnification at the wedge? Preseparator Open Questions (2) M. Hausmann, 15 Sep 2010, Slide 6

 Section from wedge to achromatic focal plane S-shape, brings the beam up from underground Original vertical offset of about 35 ft. to match tunnel depth This number likely needs to be adjusted depending on tunnel depth  Open questions Magnifications »From the front end »And into the following stages And optimization of transmission Preseparator Open Questions (3) M. Hausmann, 15 Sep 2010, Slide 7

 Wedge and momentum compression Original ‘standard’ assumption:  Momentum resolving power of > 1000 → mass resolution around straggling limit More detailed look into emittance growth raises questions »Steep wedge angle requires relatively thick wedge E.g. for 40 Mg: nominal 4.5 mm Al (d/R = 0.116) → one end 0.6 mm, the other 8.9 mm »Sizeable energy straggling ‘magnified’ by large dispersion in following section Required accuracy of wedge shaping? Preseparator Open Questions (4) M. Hausmann, 15 Sep 2010, Slide 8

 To be constructed from existing A1900 magnets 4 identical dipoles 3 types of quadrupole triplets (2 × type T1, 4 × type T2, 2 × type T4) Flexibility in layout: two stages OR one stage of higher resolving power  Optimize symmetry for two stages or single stage? T1 – D – T2 – I – T2 – D – T1 – I – T4 – D – T2 – I – T2 – D – T4 or T1 – D – T2 – I – T2 – D – T4 – I – T4 – D – T2 – I – T2 – D – T1  Best way to get through the dipole gaps? Waist/image or parallel beam in non-dipersive direction  Two stages: So far have corrected aberration at ends of stages But have remaining aberrations at wedge position »Is there a first order layout that mitigates this problem? »How bad will that hurt the transmission/beam purity? Horizontal Stages Open Questions (1) M. Hausmann, 15 Sep 2010, Slide 9

 Question about A1900 magnets So far A1900 optics not fully understood Do we have an adequate description of the magnets? Does the Enge model really apply for short quadrupoles? »Ones that have no constant field region between the fringe field »And how do you really describe these fields in an Enge model?  Some of these magnet questions also apply to new magnets for the preseparator Horizontal Stages Open Questions (2) M. Hausmann, 15 Sep 2010, Slide 10

 Diagnostics (so far only rudimentary) Detector resolutions needed? Detector placement? Resolving of charge states by tracking? Separator Overall Open Questions M. Hausmann, 15 Sep 2010, Slide 11

 Design and simulation of beam transport to experiments Connection to existing beamlines? Optimum shaping of phase space to maximize transmission?  Interdependencies between separator and downstream optics? To gas-cell range bunching? Beyond the Fragment Separator M. Hausmann, 15 Sep 2010, Slide 12

 Ion optics: COSY, GICOSY, TRANSPORT Assume that codes are fine Question is whether we have adequate descriptions of our elements? Wedge as integral part of preseparator optics so far only in COSY (not all versions)  Fast simulation of separation in LISE++ Now good for system with wedge as integral part of optics Monte Carlo mode Single magnet mode Some not tested in very much detail  Monte Carlo Simulations COSY-MC MOCADI LISE++ Toolkit Open Questions (1) M. Hausmann, 15 Sep 2010, Slide 13

 COSY-MC Calculates the optics and beam-matter interaction Finalizing coding convention to facilitate switch between ‘fitting’ and ‘MC’ Charge change induced energy loss straggling not included  MOCADI Relies on optics from other codes Charge change induced energy loss straggling included Matter thickness fluctuations included  LISE++ Monte Carlo mode Relies on optics from other codes Charge change induced energy loss straggling not included Matter thickness variation included  Plus questions about the details of the kinematics models? In particular different fission models! Toolkit Open Questions (2) M. Hausmann, 15 Sep 2010, Slide 14

 Current related milestones: Project Milestones M. Hausmann, 15 Sep 2010, Slide 15 4 April st order preseparator design with fringe fields complete 25 April 2011Benchmarking of code system complete 11 July 2011Analysis of A1900 magnets complete 2 August 2011Stages 2 and 3 layout phase 1 complete (based on what we know about magnets now) 10 February 2012Beam transport calculation to gas stopper complete 21 February 2012Stages 2 and 3 layout phase 2 complete (based on what we learned in magnet reanalysis) 15 May 2012End-to-end simulation to one end station complete

 The following pages contain some material in various states of completion that might be useful to discuss some of the questions mentioned above. Appendix M. Hausmann, 15 Sep 2010, Slide 16

 Trajectories for ± 40 mrad and ±5 % in momentum (black = nominal momentum; blue = + 5 %; red = - 5 %) Preseparator Trajectory Plot M. Hausmann, 15 Sep 2010, Slide 17 Wedge Dipole

Beam Dump Concept Beam Dump after 1 st Dipole Magnet M. Hausmann, 15 Sep 2010 All primary beams exit end of dipole; no additional beam dump necessary, Slide 18 Beam dump barrels SC Dipole (70 ton) Resistive sextupole partially protects dipole

Alternative Preseparator Front End Trajectories (1) M. Hausmann, 15 Sep 2010, Slide 19 Q Q Q D QQQ SS D DumpWedge  Dispersive plane, 3 rd order Image (dispersive) at dump right after 2 nd dipole 2 nd order term (x|ad) = 0 possible at wedge and at dump. Other aberrations corrected at the wedge.

 Non-dispersive plane Alternative Preseparator Front End Trajectories(2) M. Hausmann, 15 Sep 2010, Slide 20

 Extreme trajectories (beyond +25 % and beyond -15 %) deviate really far from the axis, but in part due to sextupole field that doesn’t exist that far out. Trajectories of different primary beams M. Hausmann, 15 Sep 2010, Slide 21  In 2 nd order, orange blocks indicate beam dump positions

Beam Spot for Bρ Beam = - 20 % M. Hausmann, 15 Sep 2010, Slide cm × 1.2 cm (sigma) Charge states ( 238 U) resolved; spaced about 1.5 cm apart

Preseparator Vertical Rise Adjustment  Developed preliminary preseparator optics to provide 40 ft. vertical rise  Steeper rise (dipole bend angle 40 ° → 55 °)  New goal might be in between 30 and 40 ft., Slide 23 M. Hausmann, 15 Sep 2010

C-bend Ion Optics  Ongoing development  Trajectories in 2 nd order  Top panel: dispersive plane  Bottom panel: non-disp. plane  Uses waist- and parallel focusing for Y in dipoles  Some remaining aberrations at wedge positions, Slide 24 M. Hausmann, 15 Sep 2010

C-bend Alternative Solution  Alternative ion optical solution for stages 2 and 3  Image aberrations corrected to 2 nd order  Improved aberration correction at wedge locations  Optimization in progress  If memory serves: less resolving power than previous version, Slide 25 M. Hausmann, 15 Sep 2010

C-bend: Single High Resolution Stage  Single stage mode of combined second and third separator stages  Improved resolving power of 2240 Achieved by eliminating images at 1 st and 3 rd focal plane  Very preliminary results Symmetric cosine-like solution in Y Reduced acceptance, Slide 26 M. Hausmann, 15 Sep 2010

 Following pages are from investigation of A1900 magnets (quite a while ago)  ‘ratios’ or ‘standard ratios’ refers to the fact that some quadrupoles (moslty in the 1 st triplet) are typically run a strengths a few percent different from the COSY calculation.  ‘tweaks’ refers to the same thing. A1900 Magnets M. Hausmann, 15 Sep 2010, Slide 27

Ray tracing 1: X as designed Without any non-unit ratios (±10,20 mrad, ±1,2%), Slide 28M. Hausmann, 15 Sep 2010

Ray tracing 2: X with “ratios” With the “standard ratios” applied to triplet 1 (same particles), Slide 29M. Hausmann, 15 Sep 2010

Ray tracing 3: Y as designed Without any non-unit ratios (±20,40 mrad, ±1,2%), Slide 30M. Hausmann, 15 Sep 2010

Ray tracing 4: Y with “ratios” With the “standard ratios” applied to triplet 1 (same particles), Slide 31M. Hausmann, 15 Sep 2010

Test Optics with Beam: Bi q-state data:  5 charge states (77 +/- 2 ?) at image 2: XYAB Y vs. XA vs. XB vs. YB vs. A Result: Dispersion OK; can gate on q-states, Slide 32M. Hausmann, 15 Sep 2010

Bi q-state data  Different q-states in focal plane Q=75Q=76 Q=77Q=78Q=79 Y vs. X A vs. X B vs. Y B vs. A (A|DD) Bit underfocused Nice focus Chromatic aberrations, Slide 33M. Hausmann, 15 Sep 2010

Check of overlapping fringe fields, Slide 34M. Hausmann, 15 Sep 2010  Scan of fields with hall probes: X-Y-X triplet

Check of overlapping fringe fields Conclusion: no significant deviation from simple superposition, Slide 35M. Hausmann, 15 Sep 2010  Compare triplet scan to superposition of scans for individual excitation

Check of overlapping fringe fields Again: no significant deviation from simple superposition, Slide 36M. Hausmann, 15 Sep 2010  Compare triplet scan to superposition of scans for individual excitation

Effective lengths, Enge functions  Radial field at given radius is function of Enge function and derivatives thereof  Reconstructed in Mathematica yielded: New Enge coefficients New effective lengths, Slide 37M. Hausmann, 15 Sep 2010 New fit (gold) agrees with data points (also gold) better than old fit (purple)

Eff. Length vs. pole tip field: B-type quadrupoles Pole tip field in Tesla Eff. Length in m Blue dots: fit to all radii data Other color dots: from single radius data Dashed line: original fit Solid line: new fit (to blue dots) Conclusion: fluctuations of a few mm between “identical” magnets Already noted by DeKamp years ago: depends on ‘environment’ (neighboring magnets), Slide 38M. Hausmann, 15 Sep 2010

MOTER/hall probe data 1 Data overlayed: on coarse scale no difference detectable, Slide 39M. Hausmann, 15 Sep 2010  Compare Hall probe scan to fields from raytracing (very high rigidity beam through field defined by Enge function)

MOTER/hall probe data 2 But in detail: there are differences, Slide 40M. Hausmann, 15 Sep 2010

In COSY with “ratios”, no changes, Slide 41M. Hausmann, 15 Sep 2010  Simply plugging the ‘ratios’ into the COSY model: changes the focusing

In COSY with “ratios”, no changes, Slide 42M. Hausmann, 15 Sep 2010

Adjustments in COSY  Now try to change other parameters in order to reproduce the experimental results with the ‘ratios’ applied  Goals: Focus conditions at image 2 and focal plane Dispersion (incl. angle) at image 2 and FP  Adjusted in several iterations: Dipole radii Effective lengths (coupled mirror-symm. Quads) B  and axial pos. of target, triplets, Slide 43M. Hausmann, 15 Sep 2010

COSY with ‘ratios’ and ‘adjustments’, Slide 44M. Hausmann, 15 Sep 2010  Best fit so far:

COSY with ‘ratios’ and ‘adjustments’, Slide 45M. Hausmann, 15 Sep 2010

Results for best fit  Dispersion basically ok (I2 and FP)  Focus positions: - 5 cm (goal = + 10 cm) (wrong direction!) + 2 cm (goal = + 4 cm) + 18 cm (goal = + 22 cm) + 8 cm (goal = + 3 cm)  Changes used to achieve this: Bρ by about 0.2% Dipole radii by about 25 mm or less Quadrupole lengths by up to 2.6 mm Target position by ~ 14 mm Triplet axial positions by up to ~ 8 mm, Slide 46M. Hausmann, 15 Sep 2010

 The following slides give some info on the fission cross sections and kinematics used in COSY-MC  Other codes use different models, so we could compare ….. Fission Model M. Hausmann, 15 Sep 2010, Slide 47

Production Cross Sections for 238 U Beam Incident on 100 mg/cm 2 C Target M. Hausmann, 15 Sep 2010, Slide MeV/u 400 MeV/u  Fission cross sections dependent on energy MCNPX

 Fission products have large emittance. Phase space resembles a hollow spherical shell. MCNPX »100 mg/cm 2 C target Fission Dynamics: 132 Sn from Fission of 238 U 200 MeV/u 400 MeV/u, Slide 49 M. Hausmann, 15 Sep 2010

 Interpolations for fission distributions based on energy of the 238 U beam, A and Z of fragment, average energy of fragment  Select random particles according to fission kinematics Fission Dynamics: 132 Sn from Fission of 238 U M. Hausmann, 15 Sep 2010, Slide 50 MCNPX Data 132 Sn Phase Space after 100 mg/cm 2 C target Interpolations of MCNPX Data 132 Sn Phase Space after 100 mg/cm 2 C target