Gas flow studies on MicroMeGaS Detectors for the NSW Upgrade Stathis K. Karentzos National Technical University of Athens, NTUA HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology

Contents  The Atlas detector Upgrade – New Small Wheel  The NSW – MicroMeGaS  2D Gas Flow Studies – NSWMM  3D Gas Flow Study – Mesh  Conclusions HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 2

The Atlas detector Upgrade – New Small Wheel Muon Small Wheel has two issues a. With the higher luminosity of the LHC Phase I upgrade (L~5x10 34 cm -2 s -1 ) the present muon end–cap Level 1 (L1) trigger rate will exceed the overall ATLAS trigger bandwidth allowance. b. The performance of the present small wheel tracking chambers, MDTs and CSCs, will be degraded in the high radiation background. Issues addressed by the New Small Wheel (NSW) upgrade… HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 3 The Muon ATLAS MicroMegas Activity (MAMMA) R&D explored the potential of the MicroMeGaS technology for its use in LHC detectors and finally proposed to equip the New Small Wheel (NSW) with MicroMeGaS detectors, combining : superb performance in high rates, excellent performance in terms of spatial resolution and efficiency, sufficiently good time resolution for triggering, very good ageing properties and the use of a non-flammable and cheap gas mixture [Ar(93%) – (7%)] at atmospheric pressure.

The NSW – MicroMeGaS The gain is reduced inversely by the increase of the quencher’s concentration… A low flow rate amplifies the effect of the electron capture phenomenon… A faulty supply will affect the performance of the detector… HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 4

5 2D Gas Flow Studies – NSWMM

6 (S)LM2 (S)LM1 outlet inlet 5mm d = 2mm 0.5mm d = 2mm Single small plane volume : m 3 = 20 L (SM1:13 L, SM2: 7 L) Singe large plane volume : m 3 = 26 L (LM1:16 L, LM2: 10 L) Total gas volume is 6 m3 (Ar:CO2 93:7 at atm. pressure) HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology

Upflow Large Sector Small Sector 7 HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology

8 Large Sector Small Sector Downflow

9 Air Ar:CO 2 Hole distance Bernoulli ‘s backstep Adhesion force HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology SM1 and SM2

Comparison a. plus 2 “outboard”holes b. without the 2 “outboard” holes 10 Air Ar:CO 2 HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology

3D Gas Flow Studies – Mesh 11 HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology

3D Gas Flow Studies – Mesh HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 12 HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 12

Conclusions  MicroMeGaS is one of the detector technologies that has been chosen (to enhance the NSW) for precision tracking and triggering purposes of the ATLAS muon forward detectors in the view of LHC luminosity increase.  Studies and flow simulation results show that the unequal gas distribution will create "dead" areas which limits the effectiveness of the detector.  The main characteristic in our studies which plays a huge role on the conservation of laminar flow, is the geometry of our chamber.  The 3D simulations confirm that the gas propagates through the mesh which is of vital importance. HEP 2014 – Conference on Recent Developments in High Energy Physics and Cosmology 13