GEM foil tensioning studies at Frascati S.Bianco M.A.Caponero A.Russo for the Frascati group Challenge 1: Develop a simple, cost-effective, mass production tool to asses GEM foils planarity and parallelism within 100um over the 1mm gap – 20-30um precision – MOIRE’ INTERFEROMETRY ? Challenge 2: Is an insitu monitoring possible ? – OPTICAL SENSORS GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 1

Tensioning vs performances Tolerances inherent in the method to stretch GEM foils and their relative positioning have an impact of the uniformity of time response Previous studies done on small area GEM foils (LHCb studies) have set mechanical precision in gap dimension and uniformity at +-10% (+- 100um for 1mm-gap), corresponding to 6% gain variation. In the case of Ar/CO 2 /CF 4 gas mixture there is a small dependance of v d on E d which translate into a small dependence of the timing performance vs the mechanical precision and tension stability. Thus is crucial to ensure the assembly precision and to study the long term stability of the foil tension from the mechanical point of view. Assembly precision: Moiré interferometry for assembly Interference patterns assure flatness and uniformity in the plane orthogonal to the foil up to better than 100um Long term stability: Optical strain gauges for long-term stability. Technique has been applied to several detectors in HEP for strain and deformations, temperature and humidity measurements. Great experience in Frascati. GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 2

Specific Q&A of G.Apolllinari Review committee The Frascati programme answered a specific question from the G.A. review committee GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 3 1) Do the tolerances inherent in the NS2 method to stretch GEM foils have an impact of the uniformity of time response? In other words, what are the specifications for foil flatness and/or tension to achieve a uniform time response ? Can those specs be achieved with the NS2 method ? 2) Can a GEM superchamber (2 GEM located ~2 cm apart) with a ~50 micron resolution provide a point+slope measurement, thus adding one more handle with the possibility of a GE1/1 self-contained muon pt trigger ? - Alexei 3) Provide a funding profile request for a project which achieve full installation in LS2 4) Drill one-level-down in the cost estimate 5) If you have it readily available, show your plan and manpower resources for a 2- chamber system installation in LS1

Previous LHCb studies have set mechanical precision in gap dimension and uniformity at +-10% (+-100um for 1mm-gap), corresponding to 6% gain variation Poli-Lener (Frascati) phD Thesis; G.Bencivenni Assembly precision and long-term stability is being studied at Frascati via Moire` interferometry for assembly Optical strain gauges for long-term stability INFN funding for 2014 secured Answer. 1 (a) continued GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 4

Gap width control GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 5 Careful control of the GEM foil flatness after tensioning – Uniformity of the Gain response on large GEM foils – Stability of operations (control of HV discharge) – Control of mechanical stresses Correlations studies between GEM performance and gap width – Effect of GEM foil sagitta on Gain/efficiency and time resolution – Parametrization of perfromance for MC modeling Study of time distribution tails – Inter-play between gas mixtures and gap widths

GEM foils flatness during assembly 6 Studies are in progress on the assessment of flatness will be performed via Moire` interferometry. – Interference patterns assure flatness and uniformity in the plan orthogonal to the foil up to better than 100um The online, fast, continuous, rad-hard, multi-plexable monitoring over GEM chamber operation might be performed via a few optical sensors applied to the GEM foils in inactive areas. Studies in progress. Technique has been applied to several detectors in HEP for strain and deformations, temperature and humidity measurements, temperature and humidity. 1.E.Basile et al., A Novel approach for an integrated straw tube-microstrip detector IEEE Trans.Nucl.Sci. 53 (2006) L.Benussi et al., The Omega-like: A novel device using FBG sensors to position vertex detectors with micrometric precision Nucl.Phys.Proc.Suppl. 172 (2007) M.Caponero et al., Use of fiber optic technology for relative humidity monitoring in RPC detectors PoS RPC2012 (2012) 073, accepted by JINST 2013 Answer. 1 (a) continued GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting

GEM foils tensioning w/ Moire` GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 7

1. Characterize Laser Displacement Sensor+optical support+optical bench systematics on a flat reference surface GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 8 LDS OPT support FLAT REFERENCE

GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 9 1. Characterize Laser Displacement Sensor+optical support+optical bench systematics on a flat reference surface LDS Laser beam Flat reference surface X Z

X-axis scan, measure Z displacement twice, back and forth GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 10 Forward scan Laser displacement [um] Support displacement in x-axis [mm]

Repeatability of LDS system over 37 mm scan is better than 4-5um in Z measurement GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 11 Support displacement along x-axis [mm] z-displacement(back) – z-displacement (forth) [um]

First estimate of Moire’ fringes sensitivity with very preliminary setup Optics arranged for a small (3cm x 3cm ) field of view (FOV). Very coarse lattice spacing. No phase-shift. Sample was displaced in Z direction GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 12 PROJECTOR CAMERA FLAT SURFACE

D6 dic 2013 Very clear Moire’ fringes Two images overlayed Reference z=0 um (background) Displaced z= 200 um (foreground, yellow box) ½ PERIOD SHIFT Sensitivity is normally ¼ period  100 um accuracy for z displacements. Can do much better with finer lattice and phaseshift GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 13

Dischi di calibrazione GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 14 X (mm) Spessore um Tastati con Laser Slope non perfetto allineamento

GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 15 Reticolo grossolano Reticolo piu’ Fine, maggiore sensitivita’ Risoluzione attuale Ottima per 300um, Molto migliore (5x) Con phase shift (hardware In consegna)

Status and prospects LDS is stable and repeatable (4-5 um) and well-suited to calibrate Moire` fringes Moire` fringes observed and being calibrated with temporary setup onloan Final setup including phase-shift and actuator ordered, delivered by January Study on large NS2 GEM foils Manpower problem for Phase-shift software, searching for undergraduate Engineer GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 16

SPARES GEM foils tensioning - S.Bianco M.A.Caponero A.Russo for the Frascati group - January 2014 Bari GEM Italy Meeting 17