NA 62 – straw detector

1. NA 62 – straw detector Content • Detector Specifications • Chamber design • Straw design and specifications • Calculations and measurements • Prototyping • Plans Straw review 16/9/2009

2. Straw tracker layout • 448x16 = 7168 straws • Operate in vacuum 2.1m long Di =9.8mm • Precise tracking (<120 μm) • Hermetic for tracks -3 degree < Q < 3 degree. Minimum diameter is 9.4 mm • Straw rate: up to 0.5 MHz • Non-flammable gas mixture • CO2 (90%)+ CF4 (5%) + Isobutene (5%) 4 chambers 4 views in each chamber 448 (4x112) straws in each view 448 (4x112) straws in each view Straw review 16/9/2009

3. Test beam in 2008 The effective radius of the straw is one important component in the straw layout. R effective=4.7 mm Straw review 16/9/2009

4. Detector assembly Straw review 16/9/2009

5. Straw proto status 40 straws out of 64 have been installed I invite you to come to 154 to look at the different prototypes and long term mechanical set-ups Straw review 16/9/2009

6. Prototype assembly detail of straw installation We test two solutions for straw insertions Key issues: leak tightness & straw straightness) Straw review 16/9/2009

7. Straw specifications • Long term mechanical stability • No or little material to limit multiple scattering. No mechanical supports • Withstand 0.5 MHz with CF4 • Work in vacuum • Resist to 1 bar over pressure for several years. • Straight straws < 200 mm (for a hermetic detector) • Support and keep pretension • Spacer every 70 cm • Gas tight to minimize pumping power (10-6 mbar) • Low permeation  protection by metal layer • No leaks (weld and straw fixations) Straw review 16/9/2009

8. Why welded straw • Classical winded straw does not work with pretension due to the creep in the joint between the two films (back-to-back gluing) . Example: ATLAS TRT, LHC-b, AMS, COMPASS • Reinforced straws more material and complicated (ATLAS TRT) Straw review 16/9/2009

9. NA62 straws • We have studied two straws • 32 mm Mylar with 200 nm Aluminum coating on both sides • 32 mm Mylar with Au/Cu copper coating on one side (200nm/500nm) • Problem with weld was discovered with the CREAM experiment in April. They have 2000 straws made from the same production line. 1% broken straws (in the weld) after 2 weeks and 1 bar overpressure • Permeation looks too high for both straws • Comment: Unfortunately the weld in the straws worked well without problem for the first prototypes (low statistics) Straw review 16/9/2009

10. Pretension straw mechanics Why we have straw deformation in vacuum (horizontal straw): Solution: pretension with enough margin allowing for creep Straw review 16/9/2009

11. Explanation The pressure in the gas (or liquid) adds a bending moment, which has to be taken by the straw wall. Always in compression if n< 0.5 Straw review 16/9/2009

12. Deformation of the straw as a function of pressure for different pre-tension and pressure Straw review 16/9/2009

13. Long term mechanical tests of the straws (~ 9 months) • Long term horizontal tests • Study the sag of the straw over time an and the tension in the straws • Long term vertical test. study the elongation of the straw test • See Sergei Movchan’s talk for more data (3.5 years)

14. Long term mechanical test results Horizontal straw 1.85 m long. Start: December 2008 Straw review 16/9/2009

15. Long term mechanical test results Absolute deformation of vertical straws (1.2m, 1.5 kg and 1 bar) Straw review 16/9/2009

16. Conclusion of the mechanical test • Adding 1 bar over pressure corresponds to a loss of tension of about 400g • This can be seen in the sag of a horizontal straw or from the frequency measurement • We have two supports for the straw, which gives 70 cm between supports • Our long term tests indicates some creep but (we believe) acceptably • It is important to measure the tension after insertion • We have a concluded that with 1.5 kg pretension (1.5 kg/mm2) we will have enough margin to keep the straw straight in tension over several years years Creep (specifications from Dupont) “Mylar® is unusually resistant to creep. Two values measured at room temperature are 0.1% after 260 hr at 2.09 kg/mm2 (2.98 kpsi) and 0.2% after 1000 hr at 2.10 kg/mm2 (3.00 kpsi). After 4000 hr at 0.35 kg/mm2 (0.50 kpsi) in 100°C (212°F) oven, a creep of 0.9% was measured.” Straw review 16/9/2009

17. QC for series production • Tension (frequency) measurement of every straw • Straw straightness measurement for every straw plane Straw review 16/9/2009

18. Straw straightness device- resultswith 1 bar Straw review 16/9/2009

19. QC tension measurement IR emitter and receiver: Tension  wf2where w is the weight per unit length and f the frequency Straw review 16/9/2009

20. Condition straw after production • 1 bar pressure for protection, handling and long term conditioning before final leak test and assembly Straw review 16/9/2009

21. Future Plans • Terminate the detailed study on the straw material and its mechanics • Build and evaluate design of the 64-straw prototype: • Verify mechanical support of the straws (and wire). Measure final straw deformation and wire off-set. Measure leak tightness • Implement new welding and QC procedure (see presentation by Sergei) • Aging/etching test of the straw (see separate presentation) • Permeation test (separate presentation) • Test the new pre-production sample from Fraunhofer (Cu/Au). It should arrive at end of October already cut in rolls • Conclude on straw material at the end of 2009 (tight!) • Beginning 2010 order the straw material • Start straw production in May 2010 • Start module-0 assembly in the fall 2010 Straw review 16/9/2009

22. Spares Straw review 16/9/2009

23. Effects of pressure Straw review 16/9/2009

24. Calculations “water hose” Straw review 16/9/2009