Na 62 straw detector
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NA 62 – straw detector. Content. Detector Specifications Chamber design Straw design and specifications Calculations and measurements Prototyping Plans. Straw tracker layout. 448x16 = 7168 straws Operate in vacuum 2.1m long D i =9.8mm Precise tracking (<120 μm )

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NA 62 – straw detector

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NA 62 – straw detector


  • Detector Specifications

  • Chamber design

  • Straw design and specifications

  • Calculations and measurements

  • Prototyping

  • Plans

Straw review 16/9/2009

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

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

Detector assembly

Straw review 16/9/2009

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

Prototype assembly detail of straw installation

We test two solutions for straw insertions Key issues: leak tightness & straw straightness)

Straw review 16/9/2009

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

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

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

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


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

Deformation of the straw as a function of pressure for different pre-tension and pressure

Straw review 16/9/2009

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)

Long term mechanical test results

Horizontal straw

1.85 m long.

Start: December 2008

Straw review 16/9/2009

Long term mechanical test results

Absolute deformation of vertical straws (1.2m, 1.5 kg and 1 bar)

Straw review 16/9/2009

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

QC for series production

  • Tension (frequency) measurement of every straw

  • Straw straightness measurement for every straw plane

Straw review 16/9/2009

Straw straightness device- resultswith 1 bar

Straw review 16/9/2009

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

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

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


Straw review 16/9/2009

Effects of pressure

Straw review 16/9/2009

Calculations “water hose”

Straw review 16/9/2009

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