1. 1 Toward a TPC for the ILD Dan Peterson Laboratory for Elementary-Particle Physics, Cornell University 20110714-LEPP-Peterson What is the ILD What is a TPC What is so special about the ILD TPC Cornell contribution: endplate

2. 2 20110714-LEPP-Peterson Cornell is part of an international collaboration, LCTPC, which has the goal of developing a TPC for a detector at ILC, or CLIC Cornell has responsibility for developing the mechanical structure for the endplate for the ILD TPC and the collaborative Large Prototypes LP1, LP2. R&D has been ongoing for about 5 years. most active

3. 3 International Linear Collider (ILC) is an e + e - machine, allowing precision measurements by directly accelerating the parton, 0.5 TeV CoM, 31 km in length, 2 detectors (“push-pull”): SiD, ILD. 20110714-LEPP-Peterson The latest schedule: TDR due early 2013 Site decision 2016 Oddly, construction is not on the map; that depends on the “decision to proceed”.

4. 4 The ILD (International Large Detector) has a TPC for the central tracker with outer radius 1808 mm, inner radius 329 mm, half length 2350 mm. 20110714-LEPP-Peterson The other detector, SiD (Silicon Detector) has, as its main feature, no gaseous tracking.

5. 5 20110714-LEPP-Peterson cathode open field cage anode magnetic field parallel to electric field track goes through leaves a trail of ionization in the gas electrons drift to anode magnetic field reduces diffusion, shape of trail of the track remains intact gas amplification of drifted electrons signals measured on pads MWPC and MPGD gas amplification What is a TPC ? Time Projection Chamber The Z projection of the track is measured in time.

6. 6 20110714-LEPP-Peterson ALICE, at LHC, has a TPC for the central tracker. The physics goals require measurement of thousands of tracks. Efficiency goal, in very dense events, is ~90%. As one can see on this cover figure, many tracks are missed. The Alice TPC has MWPC gas amplification. There are 560k pads with 2 endplates, 250 cm radius; pad size ~ 0.7 cm 2. This is typical for a MWPC TPC. This is sufficient for the resolution goal, σ(p)/p=.025 at 4GeV, translated: σ(1/p) = 6 x 10 -3 /Gev. STAR

7. 7 20110714-LEPP-Peterson The MWPC gas-amplification TPC, like that implemented in ALICE, and STAR at RHIC, is well-matched for studies of heavy ion collisions. But, precision studies at the ILC require unprecedented resolution and efficiency. The resolution and efficiency demands can be met with a Micro Pattern Gas Detector (MPGD) readout, GEM or Micromegas. Maintaining the resolution places unprecedented demands on the mechanical endplate. (explained on next few slides)

8. 8 20110714-LEPP-Peterson The precision and stability goal is ultimately based on maintaining the Higgs mass measurement. Ref. ILD LOI section 3.2.1.2 ILD momentum resolution goal (system), (1/p T ) = 2 x 10 -5 /GeV, is achieved with a TPC-only resolution, σ(1/p T ) =10 -4 /GeV (1/60 of ALICE). Ref. ILD LOI section 3.3.1 The Higgs mass measurement in e + e - -> ZH, H -> μ + μ - is affected by the momentum resolution, beam energy spectrum, and backgrounds. The width (at generator level) is 730 MeV, while the width (after track reconstruction) is 870 MeV; thus, the contribution from tracking errors is 473 MeV. σ(1/p T ) is at the significance threshold. Ref. ILD LOI section 4.3.2 (and references 86 and 87 of the ILD LOI) Maintaining the goal σ(1/p T ) requires that uncertainties in TPC measurement locations, due to magnetic field uncertainties, be limited to ~50μm. Achieving the magnetic field certainty requires decoupling the track-based magnetic field calibration from the precision mechanical calibration. And this requires a precision survey and stability of the endplate components to a similar accuracy: 50 μm.

9. 9 20110714-LEPP-Peterson from Klaus Mönig, Vienna, Nov 2005 Jet energy resolution and PFA: There are processes where WW and ZZ must be separated without beam constraints (example e + e -  WW, ZZ ) The requires a jet energy resolution of about  E/E = 30% / E 1/2 Particle Flow Analysis (PFA) achieves this resolution goal. Within a jet, charged energy is measured by the tracking; remaining neutral energy is measured in the calorimeter. Efficiency: Calorimeter hits associated with charged tracks must be matched and identified. Material: Conversion and interactions in the endplate must be minimized.  E/E = 30% / E 1/2  E/E = 60% / E 1/2

10. 10 20110714-LEPP-Peterson Goals of the ILD TPC endplate Micro Pattern Gas Detector (MPGD) readout module design - requirement driven by the momentum resolution goal MPGD gas-amplification provides a more localized signal; the pad size is 0.1 cm 2, 1/7 of ALICE. Modules must provide near-full coverage of the endplate. Modules must be replaceable without removing the endplate. Rigid – requirement is driven by the momentum resolution goal limit is set to facilitate the de-coupled alignment of magnetic field and module positions. Precision and stability of x,y positions < 50μm. Low material - limit is set by ILD endcap calorimetry and PFA, total 25% X 0 readout plane, front-end-electronics, gate 5% cooling 2% power cables 10% mechanical structure 8%. Thin – limit is again set by ILD endcap calorimetry and PFA ILD will give us 100mm of longitudinal space between the gas volume and the endcap calorimeter.

11. 11 In 2008, Cornell constructed two endplates for the LCTPC Large Prototype (LP1). Inside the chamberOutside the chamber The endplate construction was developed to provide the precision required for ILD, precision features are accurate to ~30 μm, but not to meet the material limit specified for the ILD TPC; the bare endplate has mass 18.87 kg over an area of 4657 cm 2, (mass/area) / (aluminum radiation length (24.0 g/cm 2 ) ) = 16.9% X 0, 2x the goal. Accuracy is achieved with a 5-step machining/stress-relief process developed at Cornell. 20110714-LEPP-Peterson

12. 12 These were shipped August 2008 and February 2010, and are currently in use in the LP1 TPC at DESY. 20110714-LEPP-Peterson

13. 13 This is the “equivalent-plate” design space-frame; the separating members are thin plates. This design has rigidity and material equivalent to a strut design, which has also been studied. (More on that later.) This model has a full thickness of 100mm, radius 1.8m, and a mass of 136 kg. The material thickness is then 1.34g/cm 2, 6% X 0. This meets an ILD goal. (inside view) Developed over the past year, the ILD endplate design is a space-frame and shown here as the solid model used for the Finite-Element-Analysis (FEA). 20110714-LEPP-Peterson

14. 14 This ILD endplate design results from several studies described in the following slides: ILD endplate model: FEA of the model LP1 current endplate: measurements and FEA of models LP2 space-frame designs: FEA of models, small test beams: FEA and measurements. Future studies will include construction and measurements of the new LP2 endplate. small test beams that represent one diameter of the LP2 endplate “strut” space-frame design LP1 2008 endplate “equivalent plate” space-frame design 20110714-LEPP-Peterson

15. 15 Endplate Support: outer and inner field cages deflection=0.00991 mm/100N 100N is the force on LP1 due to 2.1 millibar overpressure (area of ILD)/(area of LP1) =21.9 deflection for 2.1 millibar overpressure on the ILD TPC endplate (2200N) = 0.22 mm (220 μm). FEA calculations of deflection and stress (stress is not shown) rigidity vs thickness It was expected that the strength could be improved by asking ILD for more longitudinal space. However, the improvement with thickness diminishes (deviates from power law) above 100mm. Note small buckling in inner layer. Rigidity is improved with modest increase in the back-plate thickness. 20110714-LEPP-Peterson This is deflection; we are ultimately interested in lateral precision and stability.

16. 16 -6 -7 -5 -4 -3 -2 0 1 2 3 4 5 6 7 “deflection 1” “deflection 2” location number In the first validation of the FEA, deflection of the current LP1 endplate was measured and compared to the FEA. The load of 100N (22lbs) was placed “uniformly” in the center module location. Deflection, measured across 2 lines, agrees on average. Stress is <1% yield. 20110714-LEPP-Peterson

17. 17 Various ideas were considered for the ILD endplate. Models of LP1-like endplates were tested with the FEA mass material deflection stress kg %X 0 microns Mpa (yield: 241) LP1 18.87 16.9 33 1.5 Lightened 8.93 8.0 68 3.2 Al-C hybrid Al 7.35 7.2 (68-168) (3.2-4.8) (channeled plus fiber) C 1.29 Channeled Al 7.35 6.5 168 4.8 Space-Frame 8.38 7.5 23 4.2 (strut or equivalent plate) Study of the solid models predicts a favorable rigidity/material for the space-frame design. 20110714-LEPP-Peterson

18. Validation of the FEA with small test beams 100 mm The “equivalent plate” space-frame was constructed in carbon-fiber. 18 The concern is that the FEA may not properly treat the joints. The small test beams represent sections of the LP2 endplate across the diameter of the LP1 endplate (slide 14). For each small test beam, there is a solid model that was used for the FEA and an assembly model for construction. Deflection of the small beams was compared to the FEA. 2008 Al-C Hybrid 20110714-LEPP-Peterson

19. 19 20100408 20101111 20101104 20110202 20110316 mass center load center load center load center loaded FEA MEASURED MEASURED MEASURED mm/100N mm/100N mm/100N mm/100N LP1 0.63 kg 0.755 0.88 0.75 0.78 Al-C hybrid ( 1.0 part fiber : 1 epoxy ) 1.71 Al-C hybrid ( 0.25 part fiber : 1 epoxy ) 2.12 LP1 (channeled) 0.37 kg 2.224 2.40 (channeled for the hybrid, but without adding carbon fiber) space-frame (“strut”) 0.76 kg 0.111 0.11 0.12 space-frame (“equivalent-plate”) 0.111 0.14 Comparison of deflection for small test beams: FEA vs. measurements The standard LP1 beam agrees with the FEA, except for some problems in the first measurement, probably sloppy centering the load. The “strut” space-frame agrees with the FEA. The model accurately predicts the strength at the joints and the design is useful for ILD. The “equivalent-plate” space-frame was made with commercial carbon-fiber plates that were claimed to have the modulus of aluminum; the modulus is ~20% low. The cast-in-place carbon-fiber does not come close to having the modulus of aluminum. (Possibly, with a a heat-cured epoxy, the result would have been better.) 20110714-LEPP-Peterson

20. 20 It is possible to simply reduce the material in the LP1 endplate from 18.85kg to 7.35kg or 16.9% X 0 to 6.5 X 0, with a deflection increase to from 33 μm to 168 μm. But, when the lightened endplate design (or even the LP1 original 2008 design) is scaled up to the ILD endplate the deflection is unacceptable. Only a space-frame design provides the rigidity and material limit for the ILD. The space-frame design for LP2, with 100mm total thickness can be made with 7.5 X0 material and 23 μm deflection. When scaled up to the ILD endplate, the deflection is 220 μm. Note that I am typically measure and compare longitudinal rigidity(deflection), when we are ultimately concerned about lateral rigidity and stability. Longitudinal rigidity is readily measured in the prototypes; for now, it gives an indication of the relative lateral rigidity and stability. Lateral rigidity and stability will be monitored in longer term studies of a new LP2 endplate. 20110714-LEPP-Peterson What have we learned

21. 21 The solid model has been converted to an assembly model, compatible with LP1 modules, field cage, field cage termination, alignment devices. The “strut” space-frame is chosen because the construction is simpler. The “equivalent plate” design was developed because the FEA failed for ILD in the “strut” design. The “equivalent plate” while providing a simple model for the FEA, is more difficult and messy to construct. How does one glue in the plates beyond #3 ? There has been further lightening of the mullions. Modification of the outer scallops (from that of the original solid model) allows 2-axis, vertical tool machining. Mass: 6.56 kg in main plate, 0.81kg in back plate, 1.72kg in struts, =9.2 kg total (LP1 2008 = 18.9 kg) (Some mass is added due to the reality of the mounting fixtures and machining tools.) The next phase of prototyping/validation in the ILD endplate study: construction and measurement of a fully functional LP2 endplate in a space-frame design. 20110714-LEPP-Peterson

22. 22 20110714-LEPP-Peterson 2011-06-23: space-frame endplate main plate after first machining step. The assembly model is used as input to the machining. It is currently at the vendor, 3rd / final machining step is complete. Some corrections are required. (Some of the holes are 0.0001 inch small on one end.)

23. 23 New “module backframes” will have ~50% of the original mass, slightly more clearance. New “mounting brackets” are required to clear the strut mounts. Different versions are required for new and old module backframes. The entire assembly will be available for testing in 2012. 20110714-LEPP-Peterson

24. 24 20110714-LEPP-Peterson The new LP2 endplate (another prototype section of the ILD endplate) will be used, to further validate the FEA of the ILD endplate, and and understand complexities of the design. Studies will include deflection under load, precision and stability for in the x-y plane. Next ~3 months: The space-frame LP2endplate will be assembled in PSB 398.

25. 25 20110714-LEPP-Peterson FUTURE: We are considering jumping back into the gating studies, expanding on our earlier experience. Cornell will build a new TPC for studying wire gate designs adapted to the curved TPC module. Accepts standard LP1 modules. Other components fit in the rack: cathode, field shaping, field cage termination, ion detector.

26. 26 Summary There has been modeling and FEA at several scales of ILD development: small beams, LP1, LP2, ILD. The space-frame design is expected to provide the required rigidity and is a viable construction. A “strut” space-frame version of the LP1 endplate will be constructed this summer for further study of this possible ILD design. lateral rigidity and stability: much more work is required The new space-frame version of the LP2 endplate will be used in this study. The preliminary ILD spaceframe design can provide 0.22 mm deflection (2.1 millibar overpressure) with a contribution of 6% X 0 material (bare endplate) and 2% X 0 from the module back-frames. 20110714-LEPP-Peterson