The Development of Gaseous Detectors with Solid Photocathodes for Low Temperature Applications

Transcription

1 The Development of Gaseous Detectors with Solid Photocathodes for Low Temperature Applications L. Pereiale 1,2, V. Peskov 3, C. Iacobaeus 4, T. Francke 5, B. Lund-Jensen 3, N. Pavlopoulos 1,6, P. Picchi 1,2, F. Pietropaolo 1,7 1 CERN, Geneva, Switzerland 2 IFSI-CNR of Torino, Torino, Italy 3 Royal Institute of Technology (KTH), Stockholm, Sweden 4 Karolinska Institute, Stockholm, Sweden 5 XCounter AB, Danderyd, Sweden 6 Leonardo de Vinchi University, Paris 7 INFN Padova, Italy

2 There are several applications and fundamental researches which require for the detection of VUV light at cryogenic temperatures. Examples could be some High Energy Physics and Astrophysics experiments, noble liquid PETs, studies of cryogenic plasmas and studies of quantum phenomenas in liquid and solid He.

3 If we focus on High Energy Physics only than one of the main applications could be noble liquids TPCs and noble liquid scintillation calorimetry. TPCs are rather widely used detectors: the ICARUS experiment, the ntof experiment, WIMP search LXe/Ar detectors.

4 The principle of LAr/Xe TPC Photodetector -V Neutron VUV Track LXe Gamma Track VUV Photpodetector The detection of primary scintillation light in combination with the charge or secondary scintillation signals is a powerful technique in determining the events t=0 as well as particle/photon separation in large mass TPC detectors filled with noble gases and/or condensed noble gases. Avalanches Position-sensitive charge detector

5 LAr/Xe TPC is a very powerful detector For example, it is able to visualize tracks in 3D and measure the deposit energies

6 Long longitudinal muon track crossing the cathode plane 1.5 m 1.5 m 18 m Cathode Left Chamber Right Chamber Track Length = 18.2 m de/dx = 2.1 MeV/cm Top View 3D View 3-D 3-D reconstruction reconstruction of of the the long long track track F. Arnedo et al., Icarus collaboration, Imaging 2003 Conf. de/dx de/dx distribution distribution along along the the track track

7 Usually vacuum photomultipliers (PMTs) are used for this purpose. Drawbacks: High cost Sensitive to magnetic field

8 The aim of this work is to investigate if costly PMTs could be replaced by cheap and simple gaseous detectors with CsI and other solid photocathodes

9 Experimental set ups Two experimental set ups were used in this work: one oriented for work with cooled gases and the other one for measurements in vacuum, gases and tests with noble liquids.

10 First experimental set up: Segmented LXe module 511keV Track Planar gaseous detectors with CsI photocathodes It consists of a cryostat, inside of which a test vessel was installed. The cryostat could be cooled in a controllable way utill 90K. The test vessel was comprised of a gas scintillation chamber filled with noble gases (Ar, Xe or Kr) and contained a radioactive source ( 241 Am, 55 Fe or 90 Sr) inside, a gaseous detector with solid photocathodes attached to the scintillation chamber and the PM (EMI 9426 with a MgF2 window) monitoring the primary scintillation light produced by the radioactive sources. (cut for viewing the inner part) Dielectric plates -V +V Metallic strips Two types of photosensitive defectors were constructed, manufactured and tested: sealed detectors with MgF2 windows and windowless detectors able to operate in cooled noble gases.

11 Sealed detectors: a single wire counter or capillaries a) b) Hamamatsu capillary plate. A separately cooled cathode was used to condense and frees TMAE or TMAE+NP photocathode prior cooling the whole detector Diameter of 25 mm, thickness of 0.8 mm, diameter of holes of 100 µm

12 Photos of the main parts of the first set up (supplied by Icarus collaborators) PM with a MgF 2 window Capillary plates One of the designs of a single wire detector with a CsI photocathode. On the back of the picture- a scintillation chamber

13 Windowless detectors: CsI photocathode V1 Parallel-mesh structure V2 H2 lamp or Am a) Cascaded GEMs (or capillaries) b) Parallel-mesh detector Depening on the position of the 241 Am and the polarity of HVs, it could be used as a light souce or a charges source for gain calibrations

14 Power supplies with floating high voltages: Designed and manufactured by: C. Iacobaeus Karolinska Institute, Stockholm Tel: Price for 6 suppliers (with two HV outputs 2 kv each) ~$13000

15 Cryostat (KTH potentials) A computer controlled cryostat for ATLAS LAr calorimeter modules tests

16 However, in many cases for quick tests much simpler set up could be used, for example: A home -made cryostat for brief tests A scintillation chamber with two gaseous detectors coupled to it

17 Second set up: The second set up was a chamber which could be immersed to the bath cooled with LN 2 or other liquids. If necessary it could also be filled with noble liquids. It allows several independent studies to be carried, for example: operation of hole-type structures placed above the liquid s level, the avalanche multiplication inside the liquids, detection of the primary and the secondary scintillation lights by a PM or by a gaseous detector with solid photocathodes. In addition, it was possible to measure the QE of these photocathodes both in the vacuum and in a gas at some temperature intervals, including those, which corresponded to LXe or LAr. For this, a pulsed H 2 or a continues Hg lamp was used with a system of UV filters. The absolute intensity of the light beam was measures by calibrated Hamamatsu vacuum photodiodes and the calibrated CFM-3 counter

18 Berkeley test chamber (see Kim et al., IEEE 49 (2002)1851 and 50 (2003)1073)) HV vacuum feedthrough ~6KV in Argon gas Linear H-Vacuum translator for 241 Am source with 1mm thick SS window (60KeV photons) or a gaseous detector with a CsI photocathode ~S. Steel or ceramic construction Bakeout 24hrs, 120 o C at Vacuum: 1x10-6 Torr VUV PMT in CF 4 or CH 4 (CsTe solar blind photocathode) MgF 2 window, CaF 2 lens Vacuum pump S.S. Test Vessel S.S. Liquid Sampling cylinder

19 One of our CERN -Icarus test chamber: A chamber which could be immersed to the bath cooled with LN 2 or other liquids Double capillary plate before being installed inside the chamber Some tests, for example with GEMs, placed above LAr level, were done at Icarus LAr experimental set up

20 A simple approach: A single-wire detector with a CsI photocathode fully immersed to LN 2 and detecting UV from a candle

21 Some results obtained with the first set up:

22 Noble liquids emission spectra and typical oscillograms from the PM and the gaseous detector simultaneously recording this scintillation Gaseous dtector PM PH spectra A scintillation produced by Am: Noble liquids ( and gas ) emission spectra This is how typical results look. To extract from these oscillograms a quantative information one have to calibrate the detectors

23 QE calibration: The absolute values of the photocathode s QE were estimated from measurements made at room temperature by three methods: 1)from the measurements of the amplitude of the signal produced by the scintillation light (at very low QE the counting rate produced by single photoelectrons was used instead of the signal amplitude), 2)with respect to the known QE of the SFM-3 counter and 3)with respect to the known QE of EF and TMA (using the scintillation light from the noble gases). In the latest case the detector was filled with TMAE or EF and the amplitude of the signal produced by alpha s scintillation was measures with respect to the 55 Fe signal. Some measurements were done with the pulsed H 2 lamp.

24 First calibration procedure is described in: L. Periale et al., NIM A478 (2002) 377 and NIM A497 (2003) 242 N ph =E/W ph W ph ev For alphas of ~5 MeV N ph V s =kn ph ΩQA 1 V Fe =kn 0 A 2 K=V Fe /n 0 A 2 Vs= ( V Fe /n 0 A 2 )N ph ΩQA 1 Q=(Vs/V Fe )A 2 n 0 W ph / (EΩ A 1 )

25 QE of EF and TMA vapors used for the detector calibration in the spectral interval of nm (D. Diatroptov et al., Soviet Phys. JETF 34 (1972) 554) EF TMA (SFM-3) TheQE of the TMA vapours was measured by S Tiit (Traty Univ) at sinchrotron radoation The QE of EF vapours was measured using H - continium. V c =ka c N ph Ω c Q c V m =ka m N p hω m Q m Q m =(V m /V c )A c Ω c Q c /(A m Ω m )

26 QE of EF, TMAE and TEA used for the detector calibration in the spectral interval of nm. For comparison the QE of CsI and CuI solid photocathodes are also given Quantum efficiency (%) Wavelength (nm) CuI CsI TMAE EF TEA Q m =(V m /V c )A c Ω c Q c /(A m Ω m )

27 Example of some experimental results: signal s oscillograms without (a) and with (b) solid photocathode (H 2 lamp, EF +Ar+20%CH 4 at 1 atm) a) b)

28 Gain vs. voltage for a single capillary plate (CP) and triple GEMs both operating in pure Ar at 1 atm A similalr observations were reported by R. Chechik et al., at this Conf Gain Series1 Series2 1-a single capillary plate 2- triple GEMs Voltage (V) A single capillary plate operated stably at gains up to ~10 4. Note that earlier (at RICH-98 Conf.) we reported about some instability in operation of CPs in pure Ar. As it was found latter this was due to the residual Cs vapours used for manufacturing the SbCs photocathode inside the same chamber

29 Pulses from a parallel-mesh detector pruduced by H 2 lamp PM As was shown earlier by P. Fonte et al., that in gaseous detectors with solid photocathode breakdown accures throuh a slow mechanism- a few feedback loops. This can be exploited, especially if the detector operates not in charge, but a light multiplication mode n ph (primary photons) n 0 =n ph Q ( primaty electrons) Current amplifier N 1ph =n 0 A ph -first generation of secondary light (A=1) n 1 =n 0 A ph Q- first generation of charge (A=1) N 2ph =n 1 A ph -second generation of light n 2 =n 0 (A ph ) 2 Q-second generation of charge and so on... Usually after 3d generationa continious current appear. It could be of cource avouded by redusing the HV Ar+0.5%Xe, d=3 mm, =0.5 mm For QE estimation we used, depending on conditions, either a charge or light signals, or both.

30 Results with the first set up: QE calibration at room temperature Table 1 QE (%) of various gaseous detectors, measured with the first set up at room temperature (notes in bracket indicate the method of measuremenst:1-amplitude of signal produced by Am in Ar or Xe, 2-with respect to the QE of EF, 3-with respect to CFM-3 counter) Photocathode CsI at λ= nm (Ar Light) CsI at λ=175 nm (Xe Light) CsI at λ=165 nm (H 2 lamp) TMAE at λ= nm (Ar Light) TMAE+NP at λ= nm (Ar Light) Detector Type Single wire (Ar+CH 4 ) Single Wire in (He+H 2 ) GEM (Ar) PPAC (Ar) 19 ( 1) 37,4( 2) 2,3(1) 3.1(2) 18,3 (1) 26 (2) 23,5 (3) 0,4 (1) 0,6 (1) 2 (1) 3,2(3) 0,15 (1) 0,25 (1) 6(1) 4(3) 13 (1) 7,8(3) All other gains 100 PS. In some QE meausremenst light signal was used Note: when a single wire counter was filled with He+H 2, due to the back diffusion the measures QE was lower.

31 With cooling we simply monitor the amplitude of the signal produced by the Am scintillation light

32 Signal amplitude (due to the Am scintillation light) vs. temperature (normalized to gain 100): 4,5 1-CsI, single wire, Ar light; Signal amplitude (V) 4 3,5 3 2,5 2 1,5 1 0,5 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 2-the same, butxe light; 3-GEM, Ar light; 4-Paralel-mesh, Ar light; 5-Sm (x10), Ar light; 6-Sm, visisble light; 7-TMAE, Ar light; 8-TMAE+NP, Ar light Temperature (K) Note: at T<130K a single wire detectorsr was filled with Ar+CH 4 and at T<130K-with He+H 2. In the laters case, due to the back diffusion the measures QE was lower.

33 Table-2 Results with the second set up (H 2 lamp): QE (at 165 nm) of CsI photocathode measured with the second set up at some selected temperatures T(K) Detectors type Single wire (Ar+CH 4 ) Single wire He+H 2 Sihgle wire (vacuum) GEM (Ar) ,1 1,5 2,2 2, ,6 2,5 8

34 Measured and estimated mean QEs (under the assumption that N ph (T)= const) (all results combined together) 100 QE (%) ,1 0,01 0,001 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 Series9 Series10 1-vacuum, H 2 lamp; 2-sinle-wire, H 2 lamp; 3-Single wire, Ar light; 4-the same, Xe light; 5-GEM, Ar light; 6-parallel-mesh, Ar light; 7-Sm, Ar light; 8-Sm, visisble light; 9-TMAE, Ar light; 10-TMAE+NP, Ar light. 0, Temperatute (K) Remember that: at T<130K a single wire counter was filled with Ar+CH 4, at T<130K- with He+H 2. In the latest case, due to the back diffusion the measures QE was lower.

35 Thus, we fully confirmed our earlier results obtained with CsI photocathode operating inside noble liquids and solids

36 Earlier results: LAr, LKr, LXe test chambers (in collaboration with E. Aprile group) It was discovered that CsI photocathode can operate inside noble liquids and solids (see: E. Aprile et al., NIM 338, ; NIM 343, 1994, 129 and NIM 353, 1994, 55)

37 QE measurements: The QE of the CsI photocathode inside LXe and LKr is 2-3 times higher than in vacuum!

38 Some other our results (a parallel work with Berkeley LAr/Xe group) (for some earlier results see Kim et al., IEEE 49 (2002)1851 and 50 (2003)1073)

39 Micro -MSGC inside noble liquids: We were able to achieve avalanche multiplication, however the detector s gain gradually (~20 min) decrease due to the charging up effect. After reducing the voltage to zero and applying it again the phenome was repeated Simillar results we obtainned earlier with ordinary MSGC during a collaboration work with Coimbra Univ.

40 Spindt Cathodes: Similar geometry of our detector. Sharper tip radius ~ 0.05 µm. Array (~ 1 µm) of ~ 10,000 Cells. E Tip = ~50 M V/cm at -120V, E Drift = ~ 1000 V/cm, In Liquid Argon 6 mm E drift= ~1000 V/cm - H.V. Mesh electrode E Tip= ~50MV/cm Observed small pulses due to the avalanche multiplication at 70V for before breakdown between the electrodes (probably due to a bubble formation). Metal tips Metal gate ¾ µm Tip radius ~0.05 µm SiO 2 Silicon base ¾ µm * Courtesy of Dr. Capp Spindt, Vacuum Microelectronics Program SRI International Menlo Park, CA 94025

41 Design of a single -wire counter with a CsI photocathode used to detect light from noble liquids: CsI Cathode disc Anode wire The same single wire counter was used as in the case of our measurements with noble gases, described above MgF2 window

42 Signals from the PM and charge -sensitive amplifier: In the case of PM one can see a lot of noise pulses A copy of the page from an internal report

43 Signals from the single wire counter and charge -sensitive amplifier, detecting avalanches in noble liquids: One can see that signal to noise ratio is much better than in the case of the PM A copy of the page from an internal report

44 Some interesting effects were discovered or rediscovered (J.G. Kim et al., paper in preparation): Bubble formation during avalanche development, Dependence of the proportional region on geometry, Cathode excitation effectprobably the major effect accomponating avalanche development in LAr

45 Conclusions: We have demonstrated that gaseous detectors with solid photocathode can operate stable, depending on a design, up to 150 and even 80K. The best results (the highest QE, the highest gains gain and good stability) were obtained with a sealed gaseous detectors operating under very clean conditions. This confirmed our earlier results obtained with solid photocathodes operating inside liquid and solid noble gases. It is especially important that they have the ability to operate in magnetic fields. One can also explore avalanche multiplication inside noble liquids. All these results may allow one to significantly improve the operation and sensitivity of the TPCs and reduce their cost.

46 Possible designs CsI detectors: Results of these studies indicate that both detectors with window and windowless could be used for the detection of the primary scintillation light from noble liquids A copy of the page from the proposal to the ntof experiment

47 A possible designs of LXe PET Coimbra approach (V. Chepel et al.,) modified by replacing PMs with photosensitive gaseous detectors operating at LXe temperature