LABORATORI NAZIONALI DI FRASCATI www.lnf.infn.it The µ-RWELL: from R&D to industrialization G. Bencivenni , P. De Simone, G. Felici, M. Gatta , G. Morello , M. Poli Lener LNF-INFN G. Bencivenni, LNF-INFN

OUTLINE WP7: Muon detectors for future colliders Why a new MPGD The µ-RWELL: description and principle of operation Detector industrialization: Low-rate vs High-rate layout Financial request G. Bencivenni, LNF-INFN

Muon Detectors for future colliders The future colliders (CEPC, SppC and FCC – hh) requires for extremely large muon detectors : ~10000 m2 in the barrel 3-5000 m2 in the end-cap 300 m2 in the very forward region The detectors have to be operated in high background (very large uncertainties depending on shielding, actual structure,etc.): O(1 – 10 kHz/cm2) in the barrel O(10 – 100 kHz/cm2) in the end-cap O(1 MHz/cm2) in the forward region Taking into account the surface and the expected rates gaseous detectors and in particular MPGDs is the natural solution (straight-forward for CEPC, requiring a significant R&D for the harsher conditions of SppC & FCC-hh) R&D for HL-LHC (CMS & LHCb phase-2 muon upgrade) is clearly a good starting point G. Bencivenni, LNF-INFN

stability under heavy irradiation construction/assembly procedures Why a new MPGD The R&D on µ-RWELL is mainly motivated by the wish of improving the stability under heavy irradiation & simplify as much as possible construction/assembly procedures G. Bencivenni, LNF-INFN

The µ-RWELL architecture The µ-RWELL detector is composed by two elements: the cathode and the µ-RWELL_PCB Drift/cathode PCB Copper top layer (5µm) DLC layer (0.1-0.2 µm) R ̴50 -200 MΩ/□ Rigid PCB readout electrode Well pitch: 140 µm Well diameter: 70-50 µm Kapton thickness: 50 µm 1 2 3 µ-RWELL PCB G. Bencivenni et al., 2015_JINST_10_P02008 The µ-RWELL_PCB is realized by coupling: a “suitable WELL patterned kapton foil as “amplification stage” a “resistive stage” for the discharge suppression & current evacuation: “Low particle rate” (LR) < 100 kHz/cm2: single resistive layer  surface resistivity ~100 M/ (CMS-phase2 upgrade – SHIP  muon device @ CEPC) “High particle rate” (HR) ≥ 1 MHz/cm2: more sophisticated resistive scheme must be implemented (MPDG_NEXT- LNF & LHCb-muon upgrade  muon device @ SppC & FCC-hh) a standard readout PCB G. Bencivenni, LNF-INFN

Principle of operation top copper layer HV kapton r t  A voltage 400-500 V between the top copper layer and the grounded resistive foil, generates an electric field of ~100 kV/cm into the WELL which acts as multiplication channel The charge induced on the resistive foil is dispersed with a time constant, RC, determined by the surface resistivity,  the capacitance per unit area, which depends on the distance between the resistive foil and the pad readout plane, t the dielectric constant of the kapton, r [M.S. Dixit et al., NIMA 566 (2006) 281] The main effect of the introduction of the resistive stage is the suppression of the transition from streamer to spark by a local voltage drop around the avalanche location. As a drawback, the capability to stand high particle fluxes is reduced, but an appropriate grounding of the resistive layer with a suitable pitch solves this problem (High Rate scheme) G. Bencivenni, LNF-INFN

@ B= 0T after TRKs contribution subtraction Performance Ar/ISO=90/10 70 50 55 30 Ar/ISO =90/10, G = 2000 – point-like irradiation X-ray RWELL = (52+-6) µm @ B= 0T after TRKs contribution subtraction G. Bencivenni, LNF-INFN

The two detector layouts Low Rate High Rate single resistive layer with “edge detector” grounding “2D” current evacuation “large current path to ground”  higher resistance to ground  large Voltage drop spread  large gain non-uniformity  low rate < 100 kHz/cm2 implementation: kapton foil + PCB coupling R&D completed(*), engineering on-going (started w/ELTOS – 2016) double resistive layer with “through vias” grounding with a O(1cm2) pitch “3D” current evacuation “short current path to ground”  lower resistance to ground  small Voltage drop spread  small gain non-uniformity  high rate ≥ 1 MHz/cm2 implementation: multi-layer flex w/through-vias + PCB coupling R&D almost completed(*), engineering ready to be started G. Bencivenni, LNF-INFN

The µ-RWELL_PCB for Low Rate (CMS/SHiP) Copper layer 5 µm 1 Kapton layer 50 µm DLC layer: 0.1-0.2 µm (50-200 M/) DLC-coated kapton base material Pre-preg #106 (50 µm) 2 Krempel (25 µm) epoxy – film for surface flattening PCB (1-1.6 mm) DLC-coated base material after copper and kapton chemical etching (WELL amplification stage) 3 G. Bencivenni, LNF-INFN

Towards detector industrialization (I) LR scheme (LARGE AREA) In the framework of the CMS-phase2 muon upgrade we are developing large size µ-RWELL. The R&D is performed in strict collaboration with Italian industrial partners (ELTOS & MDT). The work is performed in two years with following schedule: Construction & test of the first 1.2x0.5m2 (GE1/1) µ-RWELL 2016 Mechanical study and mock-up of 1.8x1.2 m2 (GE2/1) µ-RWELL 2016 Construction & test of the first 1.8x1.2m2 (GE2/1) µ-RWELL 12/2017- 6/2018 ~40times larger than small protos !!! ~300 times larger than small protos !!! 1200 mm Four PCB µ-RWELL spliced with the same technique used for large ATLAS MM + only one cathode closing the detector 450 Splicing zone < 0.5 mm wide 1.2x0.5m2 (GE1/1) µ-RWELL 1.8x1.2m2 (GE2/1) µ-RWELL G. Bencivenni, LNF-INFN

Test Beam results Very preliminary G. Bencivenni, LNF-INFN Small u-RWELL Large u-RWELL G. Bencivenni, LNF-INFN

The High Rate µ-RWELL G. Bencivenni, LNF-INFN

LHCb-muon Requirements @ 2×1034cm-2 s-1 Rate up to 3 MHz/cm2 with an additional filter in front of M2 Efficiency for single gap > 95% within a BX (25 ns) Long stability up to 6 C/cm2 accumulated charge in 10 y of operation Pad cluster size < 1.2 Expected max rate MHz/cm2 (*) Active area cm2 Pad Size cm2 (*) Rate/Pad MHz # pad/gaps # gaps #chambers (with 2 gaps) M2R1 3 30x25 0.63x0.77 1.5 1536 24 12 M2R2 0.5 60x25 1.25x1.58 1 768 48 M3R1 32.4x27 0.67x1.7 M3R2 0.15 64.8x27 1.35x3.4 0.7 384 (*) average rate is about 50% of maximum rate (*) X, Y/4 w.r.t. present logical pads in M2R1-R2; a factor 2 more in Y, to halve the rate/Pad X, Y/2 w.r.t. present logical pads in M3R1 and M3R2 Same particle flux as expected at future hadron colliders

The µ-RWELL_PCB for High Rate (LHCb) Copper layer 5 µm 1 Kapton layer 50 µm DLC layer: 0.1 – 0.2 µm (50 – 200 M/) 2 2nd resistive kapton layer with ∼ 1/cm2 “through vias” density DLC-coated kapton base material 3 2nd resistive kapton layer (25µm) insulating layer (25µm) pad/strips (9-18 µm thick) readout on standard PCB (1 – 1,6 mm) “through vias” for grounding DLC-coated base material after copper and kapton chemical etching ( WELL amplification stage) 4 G. Bencivenni, LNF-INFN

Industrialization of the HR layout The industrialization of the HR version of µ-RWELL requires for a Company able to work on flexible substrate (Kapton etching , multi-layer kapton structure with through-vias … ) A good candidate (in Europe) seems to be the TECHNOLOGY TRANSFER AGENCY TECHTRA (Poland) They are specialized in GEM manufacturing: producing small and medium size GEM foils (double-mask technique) for CERN They have all the toolings for single-mask GEM foil (machine for continuous etching of kapton, laminator, UV exposure machine … testing facilities and clean room) They are interested in developing and engineering the µ-RWELL G. Bencivenni, LNF-INFN

Program Start the engineering phase of the double-resistive layer layout, with TECHTRA (flex photolithography) + ELTOS (rigid photolithography) (2017-2018) 2017: preliminary tests to fine tune the overall procedure then start the manufacturing of small/medium size (M2R1) HR protos 2018: consolidation of the manufacturing procedure and construction of large size HR proto M2R2/M3R2 (30x65 cm2) G. Bencivenni, LNF-INFN

Financial Request (2017) GOAL: n. 2 M2R1 - like size - 25x30 cm2 0.6x0.8 cm2 pad size 1500 chs/gap, partially instrumented w/VFAT2 Costs Estimate: DLCed foil 50 µm thick (ampl.stage + 1st res-layer) + 25 µm thick 2nd res-layer(Japan): 1 k€ Preliminary tests of double resistive-layer (on 10x10 cm2): 2 k€ n.2 M2R1-like protos (including DRIFT electrodes & frames): 6 k€ fee (n. 500 chs – 4 VFAT2 boards) + TURBO board: 1 k€ ___________ 10 k€ Missioni (contacts with TECHTRA/ELTOS) : 4 k€ Test Beam (4 people – 2 weeks) 8 k€ ----------------------------------------------------- 12 k€

SPARE SLIDES G. Bencivenni, LNF-INFN

Test Beam results Very preliminary G. Bencivenni, LNF-INFN Small u-RWELL Large u-RWELL G. Bencivenni, LNF-INFN

Readout-PCB production @ ELTOS GE1/1 – PCB-readouts manufatured at ELTOS 1,2 m 0,5 m G. Bencivenni, LNF-INFN

DLC sputtering on Kapton foils DLC sputtering on large Kapton foils (w/copper on one side) completed @ Be-Sputter Co., Ltd (Japan) Foil 1 (800A) Foil 2 (1300A) Foil 3 (1800A) Foil 4 (1500A) Foil 5 (1500A) Average Surface Resistivity M/ 433±90 68±9 41±12 122±22 180±17 Ar/ISO=90/10 G. Bencivenni, LNF-INFN

gluing the DLCed foils on the readout–PCBs @ MDT (Milano) Coupling the DLCed Kapton with r/o-PCBs gluing the DLCed foils on the readout–PCBs @ MDT (Milano) G. Bencivenni, LNF-INFN

GEM detector currently running @ HEP Experiment Instrumented area (m2) Gas Mixture Gain Flux (MHz/cm2) HV-type # lost sector for shorts % damaged area Front-End Electronics COMPASS 2 Ar/CO2 4000 <1 HV passive divider ??? APV25 LHCb 0.6 Ar/CO2/CF4 8000 1 HV active divider 5 (All on GEM #1) 1% CARIOCA-GEM TOTEM 6 percent level VFAT2 KLOE2 4 Ar/i-C4H10 12000 0,01 7 independent ch; then active divider 61 (8 GEM#1, 28 GEM#2, 25 GEM#3) 5% GASTONE A damaged GEM sector could required for the replacing of a whole a detector gap !! G. Bencivenni, LNF-INFN

The µ-RWELL vs GEM (Garfield simulation) GEM – Ar:CO2 70:30 gas mixture Signal from a single ionization electron in a GEM. The duration of the signal, about 20 ns, depends on the induction gap thickness, drift velocity and electric field in the gap. Signal from a single ionization electron in a µ-RWELL. The absence of the induction gap is responsible for the fast initial spike, about 200 ps, induced by the motion and fast collection of the electrons and followed by a ~50 ns ion tail. Schema di una gem … µ-RWELL – Ar:CO2 70:30 gas mixture G. Bencivenni, LNF-INFN

Muon System upgrade phase – 1b & beyond LS3: phase-1b new, high rate, muon chambers for busy regions LS4: phase-2 luminosity upgrade at ~2x1034 cm-2 s-1 muon detector response at 2×1034cm-2s-1 is seriously affected by the increased rate new shielding to reduce the rates on M2, we do expect a rate reduction of ≈ 50% new pads detectors in M2R1, M3R1 (and M2R2, M3R2) pad size X, Y/2 w.r.t. present logical pads IB removal  this would allow to cancel the ghost pads rate detailed MC studies must be done to define the final configuration profit of the very long shutdown LS3 to consolidate our Muon System with new chambers in the innermost regions  design and technology must face the luminosity upgrade of phase-2 G. Bencivenni, LNF-INFN

Strongly reduced but not completely suppressed MPGDs: stability The biggest “enemy” of MPGDs are the discharges. Due to the fine structure and the typical micrometric distance of their electrodes, MPGDs generally suffer from spark occurrence that can be harmful for the detector and the related FEE. S. Bachmann et al., NIMA A479(2002) 294 241 Am  souce Strongly reduced but not completely suppressed GEM discharge probability Efficiency & discharge probability MM 10 GeV/c proton A. Bay et al., NIMA 488 (2002) 162 Efficiency G. Bencivenni, LNF-INFN

voltage drop due to sparking Technology improvement: resistive MPGD For MM, the spark occurrence between the metallic mesh and the readout PCB has been overcome with the implementation of a “resistive layer” on top of the readout itself . The principle is the same as the resistive electrode used in the RPCs: the transition from streamer to spark is strongly suppressed by a local voltage drop. The resistive layer is realized as resistive strips capacitive coupled with the copper readout strips. voltage drop due to sparking G. Bencivenni, LNF-INFN

NS2(CERN): no gluing but still stretching … MPGDs: the challenge of large area NS2(CERN): no gluing but still stretching … A further challenge for MPGDs is the large area: the construction of a GEM requires some time-consuming (/complex) assembly steps such as: the stretching of the 3 GEM foils (with quite large mechanical tension to cope with, 1 kg/cm) the splicing of GEM foils to realize large surfaces is a demanding operation introducing not negligible dead zones (~3 mm). The width of the raw material is limited to 50-60 cm. similar considerations hold for MM: the splicing of smaller PCBs is possible, opening the way towards the large area covering (dead zone of the order 0.3 – 0.5 mm). The fine metallic mesh, defining the amplification gap, is a “floating component” stretched on the cathode (~1 kg/cm) and electrostatically attracted toward the PCB Possible source of gain non-uniformity Handling of a stretched mesh G. Bencivenni, LNF-INFN

The two detector layouts (II) single layer double layer d d’ upper layer (1cm)d’ r r d (50cm) conductive vias (*) point-like irradiation, r<<d Ω is the resistance seen by the current generated by a radiation incident in the center of the detector cell inferior layer Ω ~ ρs x d/2πr Ω’ ~ ρs’ x d’/πr Ω/ Ω’ ~ (ρs / ρs’) x d/2d’ If ρs = ρs’  Ω/ Ω’ ~ d/2d’ = 25 (*) Morello’s model: appendix A-B (G. Bencivenni et al., 2015_JINST_10_P02008) G. Bencivenni, LNF-INFN

µ-RWELL: B≠0 with Ar/ISO=90/10 CC analysis June 2015 – θ=0°, B= 0 T Dec 2014 – θ=0°, B= 0.5 T June 2015 – θ=0°, B= 1 T June 2015 - θ=0° For θ=0° and 0 < B < 1 T σ < 180 µm and ε > 98% G. Bencivenni, LNF-INFN