na 62 – straw detector

NA 62 – straw detectorContent

Detector SpecificationsChamber designStraw design and specificationsCalculations and measurementsPrototypingPlans

Straw review 16/9/2009

Straw tracker layout4 chambers4 views in each chamber448 (4x112) straws in each view

x,y,u,v x,y,u,v x,y,u,v x,y,u,v

ch 1 ch 2 ch 3 ch 4

183 m from target 10 m 10 m 15 m

Magnet MNP33

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%)

448 (4x112) straws in each view


Test beam in 2008


The effective radius of the straw is one important component in the straw layout. R effective=4.7 mm

Detector assembly


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

Prototype assembly detail of straw installation


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

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)


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)


NA62 straws We have studied two straws

I. 32 mm Mylar with 200 nm Aluminum coating on both sides

II. 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)


Pretension straw mechanics


Why we have straw deformation in vacuum

Solution: pretension with enough margin allowing for creep

(horizontal straw):


The pressure in the gas (or liquid) adds a bending moment, which has to be taken by the straw wall. Always in compression ifn < 0.5

Explanation

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


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


Long term mechanical test resultsAbsolute deformation of vertical straws (1.2m, 1.5 kg and 1 bar)

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.”

QC for series productionTension (frequency) measurement of every

straw Straw straightness measurement for every

straw plane


Straw straightness device- resultswith 1 bar


QC tension measurement


IR emitter and receiver:Tension wf2 where w is the weight per unit length and f the frequency

0 500 10000

1000

2000

Tension straw without pressure

(Frequency)^2

Tens

ion

(gra

m)

2040

0

tension

m n2 k

T

23104

25

64 n2

Condition straw after production 1 bar pressure for protection, handling and

long term conditioning before final leak test and assembly


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


Spares


Effects of pressure


Calculations “water hose”


na 62 – straw detector

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