1. Different way of gas supply for small volume MPGDs Harry van der Graaf, Fred Hartjes and Marcel Vervoort RD51 Mini workshop CERN, 24 September 2009

2. What is different for single chip MPGDs? uVery small detector volumes l1 Gossip detector ≈ 0.2 ml (15 x 15 x 1 mm 3 ) u=> very small gas flows may be used l10 volume changes/hour l=> 33 µl/min (2 ml/h) lCommercial mass flow controllers go down to ~ 2 ml/min FS n=> permit flows down to 100 µl/min uFor practical reasons we normally use bit larger flows l2 - 5 ml/min (0.12 – 0.3 l/h) 2

3. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Advantages of small flows (0.12 – 0.3 l/h) uPermitting very thin gas lines lGas lines 1/32” (≈ 0.8 mm OD) well feasible n3 m tubing 0.5 mm ID with CO 2 and 0.12 – 0.3 l/h n=> Back pressure 10 – 24 mbar lGas line of 1/64” (≈ 0.4 mm OD) not excluded n3 m tubing 0.25 mm ID with CO 2 and 0.12 – 0.3 l/h) n=> Back pressure 0.15 – 0.4 bar l(Using normal size gas pipes (6 mm OD or larger) would lead to very long reaction times) uOn site mixing of small flows hard lLong flow measurement times l(almost) out of range of commercial mass flow controllers u=> use premixed gas bottles 3 1/32” tubing

4. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes How to get premixed gas bottles? uCustom specified mixtures from commercial gas suppliers not attractive lExpensive lLong delivery time (~5 - 6 weeks) u=> We are considering gas mixing in house (Nikhef) 4

5. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Planned mixing station at Nikhef 5 Thermostat bath uEquipment lGas bottle lVacuum pump lAccurate absolute pressure sensor(s) lThermostat bath lPC for controlling valves and pressures uProcedure lEvacuate bottle lInsert gas 1 until pressure P1 lInsert gas 2 until pressure P2 + P1 lInsert gas 3 until pressure P3 + P2 + P1 lEtc.................

6. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Gas bottle uApply light weight bottle lOriginally intended for butane, propane lVolume: 12.3 l n(also bigger available (26.5 l)) lMaterial: AISI 304 (stainless steel) lTest pressure: 30 bar lBurst pressure: 120 bar lIdentification label on bottle 6 475 mm Empty weight 4.1 kg

7. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Vapour pressures vs temperature uMaximum bottle pressure often determined by condensation point lIsobutane 2.6 bar @ 15 ºC n=> Ar/iC 4 H 10 50/50 can be no more than 5.2 bar abs or 4.2 bar gauge lDME 5.1 bar @ 20 ºC nBoiling point – 24.8 ºC 7

8. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Security measures for the gas mixing station at Nikhef uCreating mixtures with flammable gases at Nikhef allowed if lDone in well vented space lExplosion detection available lProper grounding of equipment lOnly accessible for limited number of persons lThese persons are well trained lAdditional fire extinguisher is present lRisk analysis has been made lFlammable gas indication is outside lSecurity staff has been informed and instructed 8

9. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes uWe can load up to 234 l into the 12.3 l bottle lSufficient for beam test using 0.3 l/h (1 month) uBut pressure of DME and isobutane mixtures limited by vapour pressure uLimited hydrogen weight (<< 0.4 kg) l=> risk class 1 of CERN flammable gas safety manual l=> premix bottle possibly allowed in experimental area l=> short pipe lenghts =>low dead pipe volumes lEasy test beam set-up Using flammable gas mixtures at a CERN test beam MixtureP1 (bar abs) P2 (bar abs) P tot (bar gauge) Net content (l) H 2 eq. mass(g) Running time (days) at 0.3 l/h Ar/CH 4 90/10273192346.732.5 CO 2 /DME 50/504478625.412 Ar/iC 4 H 10 80/208.82.21012326.017 9 One regular (50 l) bottle with iC 4 H 10 contains 6.75 kg of H 2 equivalent mass => Risk class 2

10. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Test beam gas system with premixed bottles uAssume small flow (≤ 0.3 l/h) uFlow regulated by electronic mass flow controller (explosion proof) uFlow check (electronic mass flow sensor) at exhaust l=> verifying leaks uUpstream: thin pipes may be used (1/8”, 1/16”, 1/32”) uDownstream: thicker pipes (1/8”) 10

11. RD51 Mini workshop, CERN, September 24, 2009Fred Hartjes Conclusions uUsing low gas flows (≤ 0.3 l/h) has many advantages for lab and test beam experiments lThin gas pipes (1/8”) lPremix gas bottles in lab/ test beam area lSimple, non critical (1 channel) gas regulation lEasy and cheap experimental set-up uProducing premixed bottles at Nikhef looks feasible 11