New spark-protected GEMlike detectors with resistive electrodes V. Peskov Behalf of ALICE HMPID, ICARUS research group and TS/DEM/PMT Workshop CERN
The talk today will be about breakthrough in developments of GEM-like detectors
GEM-gas electron multiplier It belongs to a new generation of gaseous detectors called micropattern gaseous detectors
The main designs of micropattern gaseous detectors 25-100μm Microstrip gaseous detectors 25-100μm Microdot gaseous detectors 25μm 140μm MICROMEGAS GEM
Gas Electron Multiplier (GEM) 70 µm 140 µm F. Sauli, NIM A386,1997, 531 50 µm
The main feature is that the multiplication occurs not near the strips and tips or in parallel gap as in other micropattern detector (as well as in classical detectorswire type and parallel plate type) but in holes Avalanche _ + Field lines focusing effect 10 5-10 6 V/cm
Electrostatic lens in electronic optics + Electrons _
There were earlier attempts to exploit a filed line focusing effect in holes for gas multiplication
Capillary plates MCP A. Del Guerra et al.,nim A257 1987, 609
Avalanche multiplication in capillary plate Primary electrons Field focusing effect A. Del Guerra et al.,nim A257 1987, 609
Avalanche multiplication in capillary plate Field focusing effect A. Del Guerra et al.,nim A257 1987, 609
Avalanche multiplication in capillary plate Gas gain Avalanche A. Del Guerra et al.,nim A257 1987, 609
CAT- Compteur a trou F. Bartol et al., J. Phys IIII. 6,1996,337
Field lines focusing effect Gas gain Avalanche F. Bartol et al., J. Phys IIII. 6,1996,337
Another good ideas from M. Lemonier GEM Cylindrical hole-type structure M. Lemonier, Patent 2727 525,1994
Microchannel plates Avalanche Hamamatsu capillary plate. These MCP operate not in a vacuum, but in a gas atmosphere Sakurai et al., NIM, A374, 1996, 341
Gas gain of MCPs
GEM - F. Sauli, NIM A386, 1997, 531 33 cm Compass Totem NA49-future
Gas avalanches in GEM:
Features of hole-type detectors: Can operate noble gases. Can be combined with other devices of the same kind to operate in a cascade mode. Avalanche Avalanche Geometrical shielding of the avalanche light Cascaded mode
DISCHARGE STUDIES WITH MULTI-GEM DETECTORS Systematic measurement confirm that in multiple GEM structures higher gains can be sustained before discharges in presence of heavily ionizing background. Both gain and sustainable gain are increased by about one order of magnitude at each addition of a GEM. The discharge probability depends on the experiment-dependent source of background, and has to be verified in realistic running conditions. For systematic studies in the laboratory, the gain is measured with soft X-rays sources or X-ray generators, while the heavily ionizing background is emulated with an 241Am alpha source; very convenient also the use of an alpha emitter, Radon 220 (generated by natural Thorium), introduced in the gas flow http://gdd.web.cern.ch/gdd/
The main problem comes from the fact that the capacitance of the GEM is large and as a results the sparks in GEM could be as violent as in PPAC with metallic electrodes
R Energy of sparks Cu V GEM Current restriction resistors R Maximum energy: E=V 2 C/2 C~ε/d V Cu PPAC In reality the spark energy depends also on a gas and electrode s material
Discharge Protection Circuit Protection Circuit APV VFAT APV chip COMPASS TOTEM L. Ropelewski, Report at Vienne Conference, February, 2007
Multi-GEM Detectors Discharge Probability on Exposure to 5 MeV Alphas Multiple structures provide equal gain at lower voltage. Discharge probability on exposure to α particles is strongly reduced. S. Bachmann et al Nucl. Instr. and Meth. A479(2002)294 Raether limits increases in the case of the cascaded GEM L. Ropelewski, Report at Vienne Conference, February, 2007
Measures to minimize the destruction by sparking: current restriction resistors, power suppliers with fast current cut, segmentation, cascaded GEM, spark protected front- end electronics
Reasons for sparking Raethrer limit: An o >10 6-10 7 electrons. Sharp edges and imperfections. Surface streamers.
GEM Foil Defects Helsinki TOTEM Group L. Ropelewski, Report at Vienne Conference, February, 2007
Reasons for sparking Raethrer limit: An o >10 6-10 7 electrons. Sharp edges and imperfections. Surface streamers.
Raether limit for micropattern gaseous detectors The Raether limit increases with the GEM thickness V. Peskov et al., IEEE Nucl. Sci. 48,2001,1070
Thick GEM-like multipliers: THGEM L. Periale at al., NIM,A478,2002,377; J. Ostling et al.,ieee Nicl Sci.,50,2003,809 Manufactured by standard PCB techniques of precise drilling in G-10 (+other materials) and Cu etching. ECONOMIC & ROBUST! Hole diameter d= 0.3-1 mm Dist. Bet. holes a= 0.7-4 mm Plate thickness t= 0.4-3 mm A small THGEM costs ~3$ /unit. With minimum order of 400$ ~120 THGEMs. ~10 times cheaper than standard GEM. TGEM was further developed by Breskin group : R. Chechik et al. NIM A535, 2004, 303-308
Thick GEM-TGEM GEM TGEM 2 mm thick J. Ostling et al., IEEE Nucl. Sci., 50, 2003, 809
Resistive Electrode GEM- RETGEM
High resistivity layer Holes +V -V Dielectric - Resistive Electrode GEM-RETGEM +
RETGEM E=V 2 c/2 c~ε/d; c<c RPC
CNC drilling Glue PCB a) 0.4-2.5 mm Cu foil Resistive kapton 50 μm b) Contact wires Diameter of holes: 0.3-0.8 mm, pitch 0.7-1.2 mm Active area 30x30 and 70x70 mm 2 Important feature: for the first time the resistive electrodes have not any metallic substrate Surface resistivity 200-800 kω/ (100XC10E5)
Hg lamp Radioactive source PMs for monitoring discharges Window A RETGEMs GEMs Charge- sensitive or current amplifiers
Ne, 1 atm Gain 1.00E+05 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 1.00E-01 GEM 0 200 400 600 Voltage (V) RETGEM, 1mm
Ar, 1 atm Gain 1.00E+05 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 GEM 0 500 1000 1500 2000 2500 Voltage (V) RETGEM, 1mm
Ar+CO 2 Gain 1.00E+05 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 GEM RETGEM, 1mm 0 1000 2000 3000 Voltage (V)
Energy resolution of ~33% FWHM was achieved for uncollimated 55 Fe at gains of 10 3-10 4. At higher gains the detector may lose the proportionality and sometimes even works in Geiger mode
Measurements of relative energies of sparks
Measurements relative sparks energies with a current to voltage converter Metallic TGEM 1mm thick, 100 Ω feedback resistor Conclusions: 1) In Ar spark current in kapton RETGEM is almost 1000 times less 2) In kapton RETGEM initial sparks / streamers with further increase of the voltage may transit to glow discharge 3) Either sparks or streamers damage the detector or electronics Kapton RETGEM 1 mm thick, I kω feedback resistor
Signals from PM detecting light from sparks The best CrO coated TGEM (presented at ALICE Club in 2006) Regular res. kapton RETGEM
A photo of a continuous discharge in RETGEM In several cases, we initiated continuous glow discharges in the RETGEM for a total duration of 10 minutes. After the discharge was stopped (by reducing the voltage on the detector s electrodes), the RETGEMs continued to operate without any change in their characteristics, including that of the maximum achievable gain.
Double RETGEMs
Gains of single (solid symbols) and double (open symbols) kapton RETGEMs Kapton RETGEM 0. 4 mm thick 1.00E+08 Gain 1.00E+06 1.00E+04 1.00E+02 1.00E+00 Ne Ar Ar+CO 2 0 500 1000 1500 Holes 0.3 mm in diameter on a 0.7 mm pitch. Voltage (V) Kapton RETGEM 1 mm thick Gain 1.00E+06 1.00E+04 1.00E+02 Ne A Ar+CO 0 1000 2000 3000 Holes 0.8 mm in diameter with a 1.2 mm pitch Voltage (V) With double RETGEMs Raether limit for macroscopic detectors was reached : An 0 ~10 8 electrons
0.4 mm thick RETGEN can be easily bended as requers for some application, for example NA for some Photos of bended GEM for NA49 Future
Photosensitive RETGEMs
For the first time the resistive coating was covered by CsI photocathode (reflective photocathode) Window Drift mesh CsI Double RETGEMs The CsI quantum efficiency was as high as in the case of metallic substrate (~30% at 120 nm)
Gain 1.00E+06 1.00E+05 1.00E+04 1.00E+03 1.00E+02 Ar Ne Ar+CO 2 0 1000 2000 3000 Voltage (V) High gains were achieved with RETGEM coated with a CsI layer
Rate characteristics Pulse amplitude (mv) 600 400 200 0 1.00E+00 1.00E+02 1.00E+04 1.00E+06 1.00E+08 Rate (Hz/cm 2 ) Open symbols-tgem Filled symbols-retgem Stars -discharges
With rate RETGEMs behave as RPCs or MWPCs and can replace these detectors in some applications
Optimization of the RPC electrodes resistivity P. Fonte et al., NIM A413,1999,154
RETGEM may compete with GEM in many applications that do not require very fine position resolution Possible applications: Muon detection Calorimetry RICH
Possible application of LEM in classical RICH CsI Radiator The main idea: to replace wire chamber by RETGEM Drift mesh ΔV +V Advantages: simpler design, possibility to be insensitive to charge particles (at ΔV=0) New idea: radiator and the detector are placed in the same gas volume CF 4 or Ar Advantages: simpler design, More light, possibility to be insensitive to charge particles (at ΔV=0) Gas chamber Mesh CsI
Exotic applications RETGEM RETGEN can operate not only in pure noble gases, but also in air containing mixtures. This may open new fields of applications
Three examples of possible exotic applications
Flame detection
Detector of flames and sparks sealed single-wire UV counter with CsI photocathodes Developed in collaboration between CERN and Oxford Instr. Detects small flames from matches or cigarette lighter on a distance of >30m in fully illuminated rooms. Orders of magnitude more sensitive than commercially available UV flame detectors. E.g. 1000 more sensitive than Hamamatsu gas-r2868 flame detector. GAIN in Ar/10%CO 2 :~ 7 10 5 with CsI photocathode L. Periale et al., NIM, A572,207,189 V. Peskov, Report at ALICE Club, 2006
Next generation of the flame detector? (developments in progress)
Hg lamp Window Drift mesh A CsI V top TGEM A
Ar Current (na) 10000 100 1 0.01 0 500 1000 1500 2000 2500 3000 Voltage (V) Air Current (na) 1000 100 10 1 0.1 0.01 0 500 1000 1500 2000 2500 3000 Voltage (V) Sparks in air very violent, so only with RETGEM one can afford a safe operation in air
UV flame detector prototype Pulsed D 2 lamp Drift mesh Cascaded RETGEM Readout electronics
Gains of CsI coated single and double RETGEMs in air Gain 1.00E+06 1.00E+04 1.00E+02 2500 2700 2900 3100 3300 Voltage on the bottom RETGEM
Preliminary results: double RETGEM with a CsI coating is 10 time more sensitive than commercial UV sensor, for example Hamamatsu UVtron R2868 Long term stability still should be demonstrated!
Dosimetry?
Gas vessel Alpha source Ar -Vdr 4 cm Alpha tracks -V1 -V2 Double RETGEMs
Efficiency close to 95% was achieved in air in this geometry Alpha source Air -Vdr 4 cm Alpha tracks -V1 -V2 Double RETGEMs
Efficiency close to 90% was achieved in air in this geometry Alpha source -Vdr 4 cm Alpha tracks 2 cm -V1 -V2 Our G-10 detectors +V
Dangerous gases detection
Commercial photoionization detector Sensitivity: up to 100 ppb Gases: benzene, tolyene and others
Photoionization detectors are very cheap and are widely used in practice
Drift electrode Photoelectrons UV lamp G-10 detectors A Gas chamber Townsend avalanches Preliminary results: sensitivity 100 times higher than with commercial detectors was achieved for some gases
Conclusions: We have developed and successfully tested GEM-like detectors with resistive electrodes Resistive electrodes make detectors spark- protected and thus very robust and reliable in operation We discovered that resistive kapton used in these studies being coated with photosensitive layers, such as CsI, can be used as efficient photocathodes for detectors operating in a pulse counting mode. Arising from our results, we believe that GEMs with resistive electrodes will open new avenues in future developments and applications.
Spairs
T. Francke et al., NIM A508, 2003,83 Sparks quenching region
Hg lamp Radioactive source PMs for monitoring discharges Window A RETGEMs CsI GEMs Charge- sensitive or current amplifiers
Alpha source 1MΩ -V Alpha tracks 4 cm 1MΩ 10MΩ 2-5 mm 15 MΩ Resistive electrode hole-type detectors +V 1MΩ 5MΩ
A possible design of the detector for Po monitoring Surface containing Po 2-3 cm -Vdr 4 cm Alpha tracks from Po -V1 -V2 Shielding box +V Our G-10 detectors
December 19, 2006 The New York Times OP-ED CONTRIBUTOR The Smoky Bomb Threat By PETER D. ZIMMERMAN
Primary electron Entering a hole type structure -V The light from the avalanche cannot reach the cathode and thus do not create secondary electrons a) b) +V Electric field Avalanche + + + + + + c) d) Electrons from avalanches Ions remaining in the hole after the avalanche Move to the cathode They charge up the cathode, the electric field inside the hole drops and secondary electrons, even if appear do not cause secondary avalanches
Lens Window Drift electrode Photoelectrons RETGEMs Gas chamber Readout plate Strips Amplifiers
Lens Window Drift electrode Photoelectrons G-10 detectors Gas chamber Readout plate Strips Amplifiers