Latest developments of MPGDs with resistive electrodes: Developments and tests of the of microstrip gas counters with resistive electrodes R. Oliveira, 1 V. Peskov, 1,2 Pietropaolo, 3 P.Picchi 4 1 CERN, Geneva, Switzerland 2 UNAM, Mexico 3 INFN Padova, Padova, Italy 4 INFN Frascati, Frascati, Italy

It looks like nowadays (under the pressure from facts) both the GEM and MICROMEGAS communities accept that in such application as high energy physics experiments sparks in MPGDs are possible D. Neuret et al, talk at Spark workshop meeting, Saclay, S. Procurour, talk at Mini-week at CERN Reasons: Raether limit achieved due to the Landay, complex spectra of particles By geometry and gas optimization the spark rate can be done very low, but in some applications, not zero

Hence some efforts of our community should be focused on developing spark-protective MPGDs

First successful development was RETGEM R. Oliveira et al., NIM A576, 2007, 362

Large- area (10x20cm 2 ) RETGEM with inner metallic strips

See for example: R. Akimoto et al, presentation at MPGDs conference in Crete The spark protective properties of RETGEMs were confirmed by other groups

Bulk MICROMEGAS R. Oliveira et al, arXiv: and IEEE 57, 2010, 3744arXiv:

Latest design of bulk- MICROMEGS with resistive mesh

There also other efforts from various group to develop spark- protective MICROMEGAS

Always needed for gaseous detectors –Spark induced by dense ionisation cluster from the tail of the Landau –Unprotected pixel chip rapidly killed by discharges WaProt: 7µm thick layer of Si 3 N 4 on anode pads of pixel chip –Normal operation: avalanche charge capacitively coupled to input pad –At spark: discharge rapidly arrested because of rising voltage drop across the WaProt layer –Conductivity of WaProt tuned by Si doping –For sLHC BL we should not exceed 1.6*10 9 Ωcm (10 V voltage drop) –Has proven to give excellent protection against discharges WaProt Spark protection 5 layers of 1.4 µm Si 3 N 4 F.Hartjes,Report at the MPGD Conf in Crete

Very impressive developments are under way by ATLAS group T. Alexopoulos et al.,, RD51 Internal report #2010–006

MSGCs were the first micropattern gaseous detectors* They are still attractive for some applications In this report we will describe further developments in this direction: Microstrip gas counters with resistive electrodes-R-MSGC *A. Oed, NIM A263, 1988, 351

A photograph of MSGC damaged by discharges (courtesy of L. Ropelewski) One of the major problem wich standard MSGC had was their “fragility”: they can be easily destroyed by sparks appearing at gains higher than (depending on detector quality)

We have developed two designs of R-MSGC: 1)With resistive anode and cathode strips 2)With metallic anode and resistive anode strips

Cu strips 50 μm wide were created on the top of the fiber glass plate by the photolithographic method Fiber glass plates (FR-4) Then in contact with the side surfaces of each Cu strip dielectric layers (Pyralux PC1025 Photoimageable coverlay by DuPont) were manufactured; R-MSGC #1 Finally the detector surface was coated with resistive paste and polished so that the anode and the cathode resistive strips become separated by the Coverlay dielectric layer.

R-MSGC #2 First by photolithographic technology Cu strip 200 μm in width were created on the top of the FR-4 plate (Figs a and b). Then the gaps between the strips were filled with the resistive paste (Fig. c). As a next step the middle part of the Cu strips were coated with 50 μm width layer of photoresist (Fig. d) and the rest of the area of the Cu strip were etched (Fig e); in such a way metallic anode strips 50 μm in width were created. Finally the gaps between Cu anode strip and the cathode resistive strips were filled with glue FR-4 and after it hardening the entire surface was mechanically polished.

The main line which Rui pursue: to use for manufacturing R-MSGCs the same materials as for TGEMs or MICROMEGAS and similar technology to make detectors cheap and affordable

For the sake of simplicity no special care was done about edges of the strips However these parts was “enforced” by resistivity MSGC edges

Photo of R-MSGC Cu anode strip (50μm width, 400 μm pitch) and resistive cathode strips ( 200 μm width ).

Cu strips Resistive strips Ends parts of anode strips

Photo of edges of resist strips

Experimental setup Removable preamplification structure

Results obtained with R-MSGC #1

Surface streamer-old works V. Peskov et al., NIM A397,1997, 243

After additional surface cleaning

“ PPAC” mode* *F. Angelini et al., NIM A292,1990,199

Lessons we learned for tests of prototype #1 1) The maximum achievable gains are low, but sparks were mild and never destroy the detector 2)Gain limitation came from the surface streamers 3) The appearance of the surface streamers can be diminished in detectors with better surface quality and narrow anode width

Results obtained with R-MSGC#2 in Ne (Thinner anode strips, better surface quality than in R-MSGC#1)

Results obtained with R-MSGC#2 in Ne+5%CH 4

Rate characteristics Ne Ne+5%CH 4

Possible applications

Noble liquid dark matter detectors See: E. Aprile XENON: a 1-ton Liquid Xenon Experiment for Dark MatterXENON: a 1-ton Liquid Xenon Experiment for Dark Matter And A. Aprile et al., NIM A338,1994,328, NIM A343,1994,129

Event Charge hv R-COBRA with resistive electrodes CsI photocathode Shielding TGEMs with HV gating capability LXe R-TCOBRA* *See F.D. Amaro et al., JINST 5 P10002

Conclusions ●Preliminary tests described above demonstrate a feasibility of building spark protective MSGCs. In these detectors due the resistivity of electrodes and small capacity between the strips the spark energy was strongly reduced so the strips were not damaged even after a few hundreds sparks. ● The maximum gains achieved in the present designs are lower than one obtained with good quality “classical” MSGC, however more design are in course ● We are planning to apply this technology for manufacturing a CONBRA-type detectors with resistive electrodes The spark-protected COBRA will be an attractive option for the detection of charge and light from the LXe TPC with a CsI photocathode immerses inside the liquid. ● Another option for the LXe TPC, which is currently under the study in our group, is to use LXe doped with low ionization potential substances. In this detector the feedback will be also a problem and thus COBRA with resistive electrode will be also an attractive option.