Progress in the Development of Photosensitive GEMs with Resistive Electrodes Manufactured by a Screen Printing Technology

Transcription

1 Progress in the Development of Photosensitive GEMs with Resistive Electrodes Manufactured by a Screen Printing Technology P. Martinengo 1, E. Nappi 2, R. Oliveira 1, G. Paic 3, V. Peskov 1,4, F. Pietropaolo 5, P. Picchi 6 1 CERN, Geneva, Switerland 2 INFN Bari, Bari, Itali 3 Inst. de Ciencias Nucleares UNAM, Mexico 4 Ecole Superiour des Mines in St. Etienne, France 5 INFN Padova, Padova, Italy 6 INFN Frascati, Frascati, Italy

2 The development of hole- type gaseous photodetectors, (e.g. capillary plate, GEM, TGEM), combined with solid photocathodes sensitive to UV and even to visible light were successfully perused by several groups and today this direction is considering as a very promising one. Capillary plate H.Sakuria et al.,nim,a374,1996,341 GEM F. Sauli,NIM, A386,1997,531 TGEM L.Periale et al., NIM, A478,2002,377

3 Main advantages of gaseous detectors in general: Large area Insensitivity to magnetic fields The advantage of hole-type gas multipliers: In contrast to traditional gas amplification structures such as parallel-plate or wire type, the hole type detectors due to their geometric features offer strong photon and some ion feedback suppression which is essential for reaching high gas gains when the detectors are combined with photocathodes

4 Hole-type gaseous photomultipliers sensitive to visible light: (examples of early developments) Light Window SbCs photocathode CP1 D. Morman et al., NIM A504,2003,93 CP2 Amplifier Gas chamber V. Peskov et al., NIM A433,1999,492 H. Sakurai et al, Talk at Imaging 2003 Conf

5 Current mode of operation -no visible problems were discovered V. Peskov et al., NIMA433,1999,492 D. Mörmann, et al, NIM A, 504, 2003, 93

6 Problems appeared at single photon counting mode Difficulty: single photon detection thus high gain high risk of discharges

7 Want cause the problems? There are following main limitations in achieving high gas gains with photosensitive hole-type multipliers: 1)Raether limit 2) Feedbacks 3) Imperfections, jets

8 Raether limit: the maximum achievable gains of bare (no photocathodes) hole type structures A max are governed by the so-called Raether limit: A max n 0 =Q max = electrons, where n 0 is the number of primary electrons created in the drift region of the detector (Q max depends on the detector geometry and the gas composition)

9 Therefore, at gas gains 10 5 any radioactive background, natural or created during the high energy physic experiment, if it produces more than 100 primary electrons (heavily ionizing particles, showers and in some cases even minimum ionizing particles) will trigger occasional discharges (even without photocathodes!).

10 The presence of photocathodes brings another feature: Feedbacks starts contributing A f γ=1(a f γ + =1 or A f γ ph =1)- slow mechanism of discharges Typically A f <A max The probabilities γ + and γ ph are increasing with the increasing the photocathode QE and it s sensitivity to visible light (usually, UV-sensitive hole-type gas multipliers (for example, combined with CsI photocathodes) do not have too much problems with feedbacks)

11 Finally: Imperfections

12 Cathode a) Ideal holes Anode b) Holes with sharp edges c) + - Holes with debris or dust particles d) Holes with areas of slightly conductive surfaces

13 Electron jets: P. Fonte et al., IEEE Nuc. Sci 46,1999,321

14 To summarize: What cause the breakdown in hole type gas photomultipliers? In good quality UV sensitive detectors- mainly the Raether limit. In bad quality detectors-imperfections. Ion induced jets also may contribute In photodetectors sensitive to visible lightfeedbacks Conclusions: at high gains and in real radioactive environment sparks are practically unavoidable!

15 Measures to minimize the destruction by sparking: current restriction resistors, power suppliers with fast current cut, segmentation, cascaded GEM, spark protected front- end electronics Phenix experience shows that in spite of all these measures photosensitive GEMs can be damaged..

16 This is why choose another direction: we developed resistive electrodes GEM-RETGEM

17 What is RETGEM?

18 Thick GEM with resistive electrodes (RETGEM)- a fully spark protected detector TGEM RETGEM Principle of operation More about TGEM see in: L. Periale et al., NIM A478,2002,377 J. Ostling et al., IEEE Nucl. Sci 50,2003,809 R. Chechik et al., NIM A553, 2005, 35 C. Chalem et al, NIM A558, 2006, 475 Geometrical and electrical characteristics: Holes diameter mm, pitch mm, thickness mm. Resitivity: kΩ/ Kapton type: 100XC10E or a resisive layer made by a screen printed technology

19 The main advantage of these detectors is that they, due to the resistive layers, are fully sparkprotected It was also discovered that RETGEM with the cathode coated with a CsI layer has rather high QE:~30% at 120nm and ~14% at 185nm This opens possibility to build spark-protective photodetectors

20 These first prototypes were built just to demonstrate the principle. Certainly their design should be optimized for use in real life. Drawbacks of the old designs: Current flow along the surface. To avoid surface streamers we have to create dead zones. So, one cannot build an efficient large-area detector based on mosaic of these detectors This is why our further goal was to develop an approach allowing to build large-area photodetectors

21 Towards large-area RETGEMs

22 Mesh designs

23 Schematic drawing showing the feature of a new design a) G-10 plate b) Metallic strips were created mm 50x50 or 100x100mm 2 HV HV c) A resistive layer was formed by a screen printing technology and holes drilled d) The top electrode was coated with 0.35 μm CsI layer

24 P. Fonte et al., PreprintarXiv: , May 2008

25 Single-step 10x20 cm 2 mesh RETGEM Gain 1.00E E E E E E-01 Ne Ar Ar+5%CO Voltage (V)

26 Double step mesh RETGEM: 10x10 cm 2 in the top and 10x20 cm 2 on the bottom Gain 1.00E E E E E E+00 Ne Ar Voltage acroos the bottom RETGEM (V)

27 New advanced design: Strips RETGEM (S-RETGEM) It has several important advantages over the mesh RETGEM

28 Design with perpendicular strips on both sides of the G-10

29 Schematic drawing demonstrating the feature of a new design HV a) Holes are drilled in G-10 sheet b) Metallic strips were created 50x50 or 100x100mm mm mm HV c) A resistive layer was formed by a screen printing technology and holes drilled d) The top electrode was coated with 0.35 μm CsI layer

30 Resistive coating-15μm Strips thickness ~13μm Photos of the S- RETGEM

31 Design with resistive strips separated by gaps

32 Top view mm a) b) 120 mm CsI coating mm c) d)

33 Side view: Resistive coating Metallic strips CsI layer G-10 plate Holes

34 Inner metallic strips Resistive strips on the top of metallic strips

35 Cu pads for contacts

36 UV lamp Lens Window Monochromator Removable 55 Fe Drift mesh Filter HV feedthrough V dr Top S RETGEM CsI V 1 top V 2 top Gas out Gas in Bottom S RETGEM Charge sensitive amplifier

37 Gains: Filled symbols-single S-RETGEM Open symbols-double S-RETGEM 1.00E+06 Gain 1.00E E+04 Ne Ar+5%CO E+03 He+EF Ar 1.00E Voltage (V) We discovered that in He- and Ne-based gases and in the case of the inverted drift filed the S-RETGEM can operate at times higher gains than in the case of Edr=-250V/cm reaching the values of 10 5 and 10 6 with a single and double S-RETGEM, respectively. Such high gains allowed detecting single photoelectrons even with one S-RETGEM.

38 Note that in Ar- bases mixtures the operational voltages are considerably higher that in He- and Ne- based gas mixtures. Thus one can speculate that breakdown in the Ar- bases mixture is manly triggers by the hole s imperfections (sharp tips emitting electrons, dirt) whereas in He- and Nefilled detectors the Raether limit can be reached. The inversion of the electric field in the drift region allows one to suppress the contribution of the natural radioactivity and additionally increase the maximum achievable gains

39 Note also that due to the low strip capacity and the protective resistive coating, the discharges happing at gains > were exceptionally weak- their energy was almost 10 times less than n the case of the ordinary RETGEMs.

40 Strip design offers the possibility to disconnect bad channels Among several tested S-RETGEMs we had one which sparked (very mild discharges) in Ar+CO 2 mixture at rather low gains~10 2. By identifying the strips at which the discharges happened and applying the -200V negative voltage on these strips (thus lowering the voltage across the S-RETGEM in the troubled region) we were able to operate the rest of the detector area at nominal gas gains shown in the last Fig. above. We consider this experience as a possible practical method to operate detectors at high gains even if several holes have defects. It also offers the possibility of position measurements by strips readout (no needs in traditional readout plate!)

41 Position resolution: Signal (V) Strip number Thus, after optimization of the drift voltage and the gas composition we were able to reach remarkable high gas gains with S-RETGEM detectors allowing to detect single photoelectrons and make position measurements even with a single S-RETGEM!

42 QE measurements TMAE filled single-wire gas counter Hg lamp Windows Monochromator Lens CsI Double-step RETGEMs with CsI photocathode

43 Counting rate measurements from TMAE detector as function of radius Efficiency scan Counting rate (Hz) Distance from the center (mm)

44 Stability with time: 20 QE (%) Ar+5%C0 2 Ne Time (days)

45 Applications

46 RICH

47 LOI in preparation VHMPID (Very High Momentum Particele Identification Detector ) Triggering and identifying charged hadrons in 5GeV<p T <20GeV Separation between π, K, p using Cherenkov effect. Using gas n small large gas space G.. Paic et al.,, Report at the ALICE Physics Forum,

48 HMPID modules (7) VHMPID modules (2* 10 m 2 ) One Pb+Pb collision in the ALICE microscope (computer simulation)

49 Free space for the VHMPID Free space near the PHOS detector 12 modules could be inserted Maximal extension of a module: 90x140 cm 2 x 120cm Opposite side of the EMCal: away side jet correlations would become measurable, too!

50 UV visualization (in collaboration with St. Etienne group)

51 Industrial applications: visualisation of corona discharges and sparks at day-light conditions Example: a UV image of the HV corona discharge obtained with image intensifies combined with a narrow band filters. During the day time this corona is practically undetectable in the visible region of spectra

52 Forest fire The resulting loss and degradation of forested land is roughly equal to that caused by destructive logging and conversion to agriculture combined, and has wide-reaching consequences on biodiversity, health and the economy, among others. Each year, fires burn millions of hectares of forest worldwide

53 Another advanced designs- a flame detector Window Photons from flame Ar+EF vapours G-10 1 G-10 2 Amplifier Gas chamber

54 Conclusions: We presented an innovative photosensitive gaseous detector: S- RETGEM having metallic strips electrodes coated with resistivity strips Coated with CsI layers such S-RETGEMs has QE of12-14% at 185nm and operate stably (4 months observation) This approach allows: 1) to build large-area (ether the whole detector or consisting from mosaic) and fully spark-protected detectors 2) to obtain position information about avalanches directly from the RETGEM electrodes After optimization of drift voltage and the gas composition we were able to reach remarkable high gas gains with S-RETGEM detectors allowing to detect single photoelectrons and make position measurements even with a single S-RETGEM We believe that S- RETGEMs will find a lot of applications, for example, we are considering their use for the ALICE VHMPID

55 Nearest plans: 1)R&D Geometry optimization: holes pitch, thickness, strips layout Tests in C 4 F 10. CsI long-term stability studies and much more 2) Beam test

56 Backup

57 Operation with preamplification in the drift region 1.00E+06 Gain 1.00E E+04 Multiplication in drift 1.00E+03 Multiplication in holes 1.00E Voltage (V) Ne, 1 atm

58 If it is a fast mechanism, will be Raether limit valid for micropattern gaseous detectors as well? Actually the answer was unknown. Note that Raether limit was established empirically by Raether for parallel-plate avalanche detectors with large amplification gaps (>a few mm) and for a few specific gas mixtures only. What was well known that almost any type of micropattern gaseous detectors has maximum achievable gain of ~10 4 (with 55 Fe ) and all attempts to overcome this limit failed Only in ~1998 it was established that there is a charge limit in avalanche (similar to Raether limit), see: Y. Ivanchenkov et al., NIM A422,1999,300. If the total charge in avalanche overcome this limit An 0 >q max ~10 7 electrons breakdowns occur. It was an important new result

59 Counting plateau TMAE detector Counting Rate (Hz) Fe before Fe after Fe UV light TMAE detector Voltage (V) Double RETGEM

60 Hg lamp spectra, measured with TMAE (a) detector and RETGEM (b) TMAE QE vs. wavelength (c) a) c) b) Q CsI =33%N CsI /N TMAE ~ 14.5%

61 Current measurements: Hg lamp Filter Window HV feedthrough Drift mesh A CsI -V Gas out RETGEM Gas in Charge sensitive amplifier

62 Ionization chamber check (with a 185 nm filter) Current (pico A) TMAE detector RETGEM, Ne Voltage (V)

63 Focused beam Measurements of the stability of the RETGEM, using Hg as a source, at 185nm. The light is concentrated on a small slit. About 30min without light have passed between each run.

64 Summary: Aγ=1(Aγ + =1 or Aγ ph =1)-slow mechanism An 0 =10 8 electrons-fast mechanism

65 THGEM: overview Shalem et al. NIM A558 (2006) 475 & NIM A558 (2006) 468 Cortesi et al. 2007_JINST_2_P09002 Alon et al. 2008_JINST_3_P ) Large holes larger than e- diffusion full e - collection efficiency from conversion gap/photocathodes good energy resolution with ionizing radiation efficient electron transfer effective cascading of electrodes optimal geometry: hole diameter = thickness 2) Large multiplication factors in most gases incl. noble gases single electrons Single THGEM Gain Double THGEMs gain soft x-rays Single THGEM 5x10 3 Double THGEM 5x10 4 3) Rate capability:~10mhz/mm ~10 4 in Ar/CH 1atm with single photoelectrons 4) Fast response 5) Localization resolution (x-rays): 0.7mm FWHM for 0.5mm dia 1mm pitch & 2mm readout pitch.

66