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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

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
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
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

Detector assembly

Straw review 16/9/2009

straw proto status
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
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
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
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
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
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
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 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
Long term mechanical test results

Horizontal straw

1.85 m long.

Start: December 2008

Straw review 16/9/2009

long term mechanical test results1
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
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
QC for series production
  • Tension (frequency) measurement of every straw
  • Straw straightness measurement for every straw plane

Straw review 16/9/2009

qc tension measurement
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
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
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
Effects of pressure

Straw review 16/9/2009

calculations water hose
Calculations “water hose”

Straw review 16/9/2009