- Email: [email protected]
Sector multipad prototype of the FMD-MCP detector for ALICE
Nuclear Instruments and Methods in Physics Research A 419 (1998) 654—659
Sector multipad prototype of the FMD-MCP detector for ALICE A.E. Antropov, A.V. Fedotov, G.A. Feofilov *, E.K. Izrailov, V.A. Kasatkin, W. Klempt , A.A. Kolojvari, M.P. Larin, V. Lazarev, I.A. Novikov, S.V. Potapov, O.I. Stolyarov, F.A. Tsimbal, T.A. Tulina, F.F. Valiev, L.I. Vinogradov CERN, Geneva, Switzerland Granit Sci. Res. Inst., St.Petersburg, Russia VNIIM, St.Petersburg, Russia Analitpribor Sci. Res. Inst., St.Petersburg, Russia St.Petersburg State University, St.Petersburg, Russia
For the ALICE collaboration
Abstract We present results of the technology, manufacturing and first tests of a novel MCP-based sector prototype for the forward multiplicity detector for the ALICE experiment at the LHC. The detector provides better than sqrt(M)/M resolution for high multiplicity events, and about 50 ps timing resolution. Two sector MCPs are mounted on a 200 lm ceramics board with the multipad readout integrated with a passive summator. The setup is baked under 300°C and then sealed into a thin wall (200 lm) stainless-steel vacuum sector chamber with a Ti getter keeping a vacuum of 10\ Torr. A new technology of Al coating is applied in order to reduce the hydrogen leakage through the chamber walls. New multichannel ceramics feedthroughs were also developed for the signal readout and voltage supply. The results of the first in-lab and in-beam tests are discussed. 1998 Elsevier Science B.V. All rights reserved.
1. Introduction The Forward Multiplicity Detectors (FMD) of ALICE [1,2] aim at measuring the distribution of the multiplicity over the rapidity outside the central acceptance. The FMD should also provide the information to the first-level trigger based on a centrality criterium. Such an important function as the primary Z-vertex coordinate determination is also expected provided the necessary high timing resolution of the FMD is obtained. Additionally, there
* Corresponding author.
should be such possible capabilities as the beam—gas interaction suppression and pile-up rejection in order to protect much slower ITS and TPC detectors during the drift time. Model simulations of multiplicity distributions expected in Pb—Pb collisions and time-of-flight (TOF) spectra of charged particles reaching the FMD surface from the collision point were done [3] using a standard event generator based on the quark—gluon string model. They showed that in high multiplicity events expected in Pb—Pb collisions the rise time of the TOF spectrum could be less than 50—100 ps, which indicates the possible application of detectors of high time resolution. Several FMD
0168-9002/98/$19.00 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 8 ) 0 0 8 6 2 - 6
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
options were considered initially, among those there was the one which is well proved: silicon pad detectors [4—6,12]. The present choice of the Microchannel Plate Detector (MCP) is motivated by the capability to satisfy all the requirements imposed by the experiment: MCPs can provide an extremely fast [7,8], radiation-hard and compact multiplicity detector which can be placed close to the interaction point covering a wide range of pseudorapidities [2,9]. In the design for ALICE the MCP detectors are made of several similar disks with segmented anodes placed around the beam pipe between 60 and 145 cm from the interaction point, covering the pseudorapidity range from 1.5 to 4.7 (see Fig. 1). Lead—glass plates of 700 lm thickness with many 6—12 lm diameter channels are placed in high vacuum thin-wall chamber and biased by a potential of around 1000—1500 V. In the present study, we used the sector type MCPs with the following parameters: channel diameter, 12 lm; channel pitch, 18 lm; channel bias angle, 8°; thickness, 800 lm; gain, 10; bias voltage, 950—1000 V; resistance, 200—500 M); sector angle, 15°; sector height, 53.4 mm; sector base, 43.0 mm. The lowmass compact FMD-MCP with the multichannel fast readout enclosed in the independent thin-wall metal vacuum chamber and posessing a Ti-getter micro-pump is a novel device for HEP applica-
Fig. 1. Conceptual design of the one half of the FMD-MCP third disk for ALICE.
655
tions. The sector prototype was chosen to be a cost-effective option for initial studies.
2. Design of the FMD-MCP sector prototype The photo of the sector prototype prepared for the final hermetisation is shown in Fig. 2: This UHV design includes: E sector thin-wall stainless-steel chamber with anti-hydrogen protective coating and Ti-getter, E sector chevron compact MCP setup, E sector multipad readout integrated with the passive summator, E multichannel ceramics feedthroughs. The non-standard multichannel ceramics feedthroughs (MCCFs) were specially developed for the sector FMD-MCP prototype. They include: 1 coaxial (50 ), UHF design), 4 high-voltage (3 kV), 16 signal ((300 MHz) and 2 technological vacuum feedthroughs integrated in one insulating ceramic plate manufactured from radio-frequency high-vacuum ceramic (see Fig. 2). The minimum thickness of the camera stainless-steel wall, ensuring protection from diffusion penetration of atoms of hydrogen should be about 0.5—0.7 mm. However the application of special protective antihydrogen coating reduces this thickness to below 300 lm [10]. The UHV test module was developed on the base of the ultra high vacuum system UNI-5S RIBER [11] in order to control the vacuum tightness and the residual gas composition for the test samples. Several vacuum thin-wall chamber prototypes were produced and tested. The dynamics of baking (250—300°C) were studied for the prototypes. The time dependence of the residual pressure during the annealing measured at different stages of this process shows that the necessary remaining pressure level below 5;10\ Pa can be achieved. The main load in the procedure of chamber annealing was created by the MCPs. The increase of the annealing duration is approximately 400 h (nearly 12 workdays) compared to the empty chamber (100 h in case of continuous baking). A chamber residual gas
X. SPECIAL DETECTORS
656
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 2. Photo of the FMD-MCP sector prototype in preparation for the final enclosure into the thin-wall vacuum sector chamber.
mass spectrum was measured at the given level of pressure in order to understand the characteristics of the materials used in the detector and to understand possible ultra-weak leaks in the control volume of the module. The sensitivity of the mass-filter QMM-17 on the peak M/e"28 is not lower than 10\ Pa. Changes of the partial pressure for M/e"2, 12, 14 were found to be the most essential for the choice of the getter pump.
3. Development and vacuum tests of the Ti-getter Several types of possible getters were studied. A Ti-getter was found to be the most efficient one for a given measured spectral composition of the residual gas that was measured for the metal chamber with the MCP setup. We have tested the active material chosen for the getter, made of Ti by methods of powder metallurgy. Sorption speed of about 60 cm/s per cm of Ti-getter surface at 25°C was found for H and 183.3 cm/s per cm for CO . Long-term dynamics of the residual pressure rise inside the 1 l volume glass-wall chamber with the tested Ti-getter module was measured after 80, 120, 160 and 220 days (for 20.12.97). The pressure was
Fig. 3. Photo of the sector thin wall vacuum chamber of the prototype FMD-MCP detector (30° sector with one small area FMD-MCP prototype of 1 cm mounted inside) before the processes of annealing and getter activation.
being kept at better than 10\ Torr. These first results are very promising and studies are to be continued. One of the sector type (30°) FMD-MCP prototype chambers equipped with the Ti-getter pump and described above is shown in Fig. 3. The inner side of the chamber and of the feedthrough plane was coated by an anti-hydrogen protective layer of Al as described above. (The small-area
657
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 4. Typical mass spectrum of residual gases (300°C) in the test module after warming up (48 h) of the prototype of the chamber of the detector measured at P"4;10\ Pa.
FMD-MCP prototype is mounted inside.) A typical mass spectrum of the residual gas obtained after 48 h annealing of the UHV test module with the thin-wall metal chamber is presented in Fig. 4. Results confirm the choice of a Ti-getter possessing the high H sorption capability.
Table 1 The mean intensity of the protons on the detector versus scattering angle, for an Au target (10 mg/cm foil) and the primary beam intensity of 50 nA h, lab
5°
10°
15°
20°
25°
30°
Protons 6.7;10 4.2;10 8.3;10 2.7;10 1.1;10 5.4;10
4. In-beam tests of FMD-MCP prototypes FMD-MCP prototypes were tested initially at the low-energy beams of protons and a-particles of the university cyclotron. The intensity of the particles coming to the detector was controlled by a variable scattering angle (see Table 1). The intensity could also be easily changed by a factor of 100 by using another (thinner) Au target inside the chamber. One should take into account the time structure of the beam which means that the real ‘instant’ intensities (during the ‘micro-bunch’ duration of 10 ns) could be 30 times higher. This leads to a very interesting possibility of a controllable multiplicity per ‘microbunch’ application and electronics can be tested in an environment similar to that of the future LHC (in terms of beam time structure and ‘simultaneous’ load). One has to use a very fast ADC in order to have the possibility to study the counting rate capabilities of the FMDMCP prototype above 10 counts/s and to analyze the efficiency at high multiplicity rates for a single pad. Therefore a special electronic module was de-
veloped to match the counting rates with the available ADC. The principal scheme is represented in Fig. 5. The pecularities of the cyclotron beam time structure are used providing the registration of a signal for every 1024th microbunch. During the proton runs the following spectra were measured: E Background spectra (experimental hall and selfnoise). E Spectra of amplitudes of signals induced by aparticles from the Pu source positioned before the Al foil. E Spectra of amplitudes of signals induced by protons under the variable intensity. A sample of an amplitude spectrum of one of the measured output pulses obtained from the MCP chevron setup is represented below (Fig. 6). Tests have shown that the UHF performance of the FMD-MCP setups is achieved: the signal duration for the given FMD-MCP test structure was obtained to be about 2 ns and the signal rise time is
X. SPECIAL DETECTORS
658
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 5. The principal scheme of the scaling module that provides the 1 : 1024 dumping of the counting rate at high intensities amplitude spectra monitoring.
Fig. 6. Spectrum shape of signals from the FMD-MCP prototype induced by a-particles from the Pu a-source
better than 500—700 ps. Proton spectra were normalised to charged particles beam integrator counts used for measurements of the intensity of the primary proton beam. The first studies of the gain stability versus protons rate showed that for the given type of MCPs (500 M)) one can get 1.5;10 counts/s for 1 cm FMD-MCP pad anode for 50%
gain decrease. These studies are to be continued with the application of another type of MCPs (in particular with 70 M) resistance and a relevant faster channel recovery time). Further in-beam tests are also planned for the sector FMD-MCP prototypes to measure the multiplicity and the time resolution using the available beams.
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
5. Conclusions E Technical design and technology were developed for manufacturing a FMD-MCP prototype satisfying all requirements of UHV and UHF applications. E The first results obtained in long-term studies for the indpendent Ti-getter micro pump placed inside the 1 l volume during 240 days are very promising. (The pressure is being kept at better than 10\ Torr.) E In-beam tests of the small-area prototypes were started at the university cyclotron with controllable intensities of incoming particles (up to 10 particles/s). E Further in-beam tests are planned for the sector FMD-MCP prototypes to measure the multiplicity and the time resolution.
Acknowledgements Authors are indebted to J. Schukraft, O. Villalobos-Bailie and V. Lenti for useful discussions. This project is supported by the International Science and Technology Center, Grant No.345.
References
659
[2] N. Ahmad et al., ALICE technical proposal, CERN/ LHCC/95-71, LHCC/P3, Chs. 7 and 9, 15 December 1995. [3] G. Feofilov, T. Tulina, E. Zabrodin, Model simulations of the TOF spectra and timing resolution of the FMD, Internal Note ALICE/FMD, 1997. [4] R. Brockmann, Proc. Conf. of Physics and Astrophysics of Quark—Gluon Plasma, World Scientific, Singapore, 1988, pp. 617-623. [5] T.F. Gunzel et al., A silicon pad counter for first level triggering in ultrarelativistic proton—nucleus and nucleus—nucleus collisions, Preprint HD-PY-91/6, 20 November 1991. [6] B. Alessandro et al., Nucl. Instr. and Meth. A 360 (1995) 189. [7] L.G. Efimov et al., Fast ALICE L0 Trigger, Proc. 2nd Workshop on Electronics for LHC Experiments, Balatonfured, 23—27 September 1996, CERN/LHCC/96-39, p. 166. [8] L.G. Efimov et al., Fast front-end L0 trigger electronics for ALICE FMD-MCP: tests and performance, Proc. 3rd Workshop on Electronics for LHC Experiments, London, 22—26 September, 1997, CERN/LHCC/97-80, 21 October 1997, p. 359. [9] A. Kolozhvari, T. Tulina, F. Valiev, Determination of multiplicity with microchannel plate detector at the LHC. statistical approach, ALICE/93-15, Internal Note/MCP, 30 January 1993. [10] M.P. Larin, Preparation of thin film coatings allowing 10 reduction in gas emission on the surfaces of ultra-high vacuum systems, Proc. VUOTO Conf., vol XX, (N2), Aprile-Giugno, 1990, p. 310. [11] Surface Analysis System LAS Series, RIBER SA. B 268E 7/80. [12] P. Giubellino et al., Nucl. Instr. and Meth. A 279 (1989) 259.
[1] N. Antoniou et al., Letter of intent for a large ion collider experiment, CERN/LHCC/93-16,LHCC/I 4,1 March 1993.
X. SPECIAL DETECTORS
Sector multipad prototype of the FMD-MCP detector for ALICE A.E. Antropov, A.V. Fedotov, G.A. Feofilov *, E.K. Izrailov, V.A. Kasatkin, W. Klempt , A.A. Kolojvari, M.P. Larin, V. Lazarev, I.A. Novikov, S.V. Potapov, O.I. Stolyarov, F.A. Tsimbal, T.A. Tulina, F.F. Valiev, L.I. Vinogradov CERN, Geneva, Switzerland Granit Sci. Res. Inst., St.Petersburg, Russia VNIIM, St.Petersburg, Russia Analitpribor Sci. Res. Inst., St.Petersburg, Russia St.Petersburg State University, St.Petersburg, Russia
For the ALICE collaboration
Abstract We present results of the technology, manufacturing and first tests of a novel MCP-based sector prototype for the forward multiplicity detector for the ALICE experiment at the LHC. The detector provides better than sqrt(M)/M resolution for high multiplicity events, and about 50 ps timing resolution. Two sector MCPs are mounted on a 200 lm ceramics board with the multipad readout integrated with a passive summator. The setup is baked under 300°C and then sealed into a thin wall (200 lm) stainless-steel vacuum sector chamber with a Ti getter keeping a vacuum of 10\ Torr. A new technology of Al coating is applied in order to reduce the hydrogen leakage through the chamber walls. New multichannel ceramics feedthroughs were also developed for the signal readout and voltage supply. The results of the first in-lab and in-beam tests are discussed. 1998 Elsevier Science B.V. All rights reserved.
1. Introduction The Forward Multiplicity Detectors (FMD) of ALICE [1,2] aim at measuring the distribution of the multiplicity over the rapidity outside the central acceptance. The FMD should also provide the information to the first-level trigger based on a centrality criterium. Such an important function as the primary Z-vertex coordinate determination is also expected provided the necessary high timing resolution of the FMD is obtained. Additionally, there
* Corresponding author.
should be such possible capabilities as the beam—gas interaction suppression and pile-up rejection in order to protect much slower ITS and TPC detectors during the drift time. Model simulations of multiplicity distributions expected in Pb—Pb collisions and time-of-flight (TOF) spectra of charged particles reaching the FMD surface from the collision point were done [3] using a standard event generator based on the quark—gluon string model. They showed that in high multiplicity events expected in Pb—Pb collisions the rise time of the TOF spectrum could be less than 50—100 ps, which indicates the possible application of detectors of high time resolution. Several FMD
0168-9002/98/$19.00 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 8 ) 0 0 8 6 2 - 6
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
options were considered initially, among those there was the one which is well proved: silicon pad detectors [4—6,12]. The present choice of the Microchannel Plate Detector (MCP) is motivated by the capability to satisfy all the requirements imposed by the experiment: MCPs can provide an extremely fast [7,8], radiation-hard and compact multiplicity detector which can be placed close to the interaction point covering a wide range of pseudorapidities [2,9]. In the design for ALICE the MCP detectors are made of several similar disks with segmented anodes placed around the beam pipe between 60 and 145 cm from the interaction point, covering the pseudorapidity range from 1.5 to 4.7 (see Fig. 1). Lead—glass plates of 700 lm thickness with many 6—12 lm diameter channels are placed in high vacuum thin-wall chamber and biased by a potential of around 1000—1500 V. In the present study, we used the sector type MCPs with the following parameters: channel diameter, 12 lm; channel pitch, 18 lm; channel bias angle, 8°; thickness, 800 lm; gain, 10; bias voltage, 950—1000 V; resistance, 200—500 M); sector angle, 15°; sector height, 53.4 mm; sector base, 43.0 mm. The lowmass compact FMD-MCP with the multichannel fast readout enclosed in the independent thin-wall metal vacuum chamber and posessing a Ti-getter micro-pump is a novel device for HEP applica-
Fig. 1. Conceptual design of the one half of the FMD-MCP third disk for ALICE.
655
tions. The sector prototype was chosen to be a cost-effective option for initial studies.
2. Design of the FMD-MCP sector prototype The photo of the sector prototype prepared for the final hermetisation is shown in Fig. 2: This UHV design includes: E sector thin-wall stainless-steel chamber with anti-hydrogen protective coating and Ti-getter, E sector chevron compact MCP setup, E sector multipad readout integrated with the passive summator, E multichannel ceramics feedthroughs. The non-standard multichannel ceramics feedthroughs (MCCFs) were specially developed for the sector FMD-MCP prototype. They include: 1 coaxial (50 ), UHF design), 4 high-voltage (3 kV), 16 signal ((300 MHz) and 2 technological vacuum feedthroughs integrated in one insulating ceramic plate manufactured from radio-frequency high-vacuum ceramic (see Fig. 2). The minimum thickness of the camera stainless-steel wall, ensuring protection from diffusion penetration of atoms of hydrogen should be about 0.5—0.7 mm. However the application of special protective antihydrogen coating reduces this thickness to below 300 lm [10]. The UHV test module was developed on the base of the ultra high vacuum system UNI-5S RIBER [11] in order to control the vacuum tightness and the residual gas composition for the test samples. Several vacuum thin-wall chamber prototypes were produced and tested. The dynamics of baking (250—300°C) were studied for the prototypes. The time dependence of the residual pressure during the annealing measured at different stages of this process shows that the necessary remaining pressure level below 5;10\ Pa can be achieved. The main load in the procedure of chamber annealing was created by the MCPs. The increase of the annealing duration is approximately 400 h (nearly 12 workdays) compared to the empty chamber (100 h in case of continuous baking). A chamber residual gas
X. SPECIAL DETECTORS
656
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 2. Photo of the FMD-MCP sector prototype in preparation for the final enclosure into the thin-wall vacuum sector chamber.
mass spectrum was measured at the given level of pressure in order to understand the characteristics of the materials used in the detector and to understand possible ultra-weak leaks in the control volume of the module. The sensitivity of the mass-filter QMM-17 on the peak M/e"28 is not lower than 10\ Pa. Changes of the partial pressure for M/e"2, 12, 14 were found to be the most essential for the choice of the getter pump.
3. Development and vacuum tests of the Ti-getter Several types of possible getters were studied. A Ti-getter was found to be the most efficient one for a given measured spectral composition of the residual gas that was measured for the metal chamber with the MCP setup. We have tested the active material chosen for the getter, made of Ti by methods of powder metallurgy. Sorption speed of about 60 cm/s per cm of Ti-getter surface at 25°C was found for H and 183.3 cm/s per cm for CO . Long-term dynamics of the residual pressure rise inside the 1 l volume glass-wall chamber with the tested Ti-getter module was measured after 80, 120, 160 and 220 days (for 20.12.97). The pressure was
Fig. 3. Photo of the sector thin wall vacuum chamber of the prototype FMD-MCP detector (30° sector with one small area FMD-MCP prototype of 1 cm mounted inside) before the processes of annealing and getter activation.
being kept at better than 10\ Torr. These first results are very promising and studies are to be continued. One of the sector type (30°) FMD-MCP prototype chambers equipped with the Ti-getter pump and described above is shown in Fig. 3. The inner side of the chamber and of the feedthrough plane was coated by an anti-hydrogen protective layer of Al as described above. (The small-area
657
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 4. Typical mass spectrum of residual gases (300°C) in the test module after warming up (48 h) of the prototype of the chamber of the detector measured at P"4;10\ Pa.
FMD-MCP prototype is mounted inside.) A typical mass spectrum of the residual gas obtained after 48 h annealing of the UHV test module with the thin-wall metal chamber is presented in Fig. 4. Results confirm the choice of a Ti-getter possessing the high H sorption capability.
Table 1 The mean intensity of the protons on the detector versus scattering angle, for an Au target (10 mg/cm foil) and the primary beam intensity of 50 nA h, lab
5°
10°
15°
20°
25°
30°
Protons 6.7;10 4.2;10 8.3;10 2.7;10 1.1;10 5.4;10
4. In-beam tests of FMD-MCP prototypes FMD-MCP prototypes were tested initially at the low-energy beams of protons and a-particles of the university cyclotron. The intensity of the particles coming to the detector was controlled by a variable scattering angle (see Table 1). The intensity could also be easily changed by a factor of 100 by using another (thinner) Au target inside the chamber. One should take into account the time structure of the beam which means that the real ‘instant’ intensities (during the ‘micro-bunch’ duration of 10 ns) could be 30 times higher. This leads to a very interesting possibility of a controllable multiplicity per ‘microbunch’ application and electronics can be tested in an environment similar to that of the future LHC (in terms of beam time structure and ‘simultaneous’ load). One has to use a very fast ADC in order to have the possibility to study the counting rate capabilities of the FMDMCP prototype above 10 counts/s and to analyze the efficiency at high multiplicity rates for a single pad. Therefore a special electronic module was de-
veloped to match the counting rates with the available ADC. The principal scheme is represented in Fig. 5. The pecularities of the cyclotron beam time structure are used providing the registration of a signal for every 1024th microbunch. During the proton runs the following spectra were measured: E Background spectra (experimental hall and selfnoise). E Spectra of amplitudes of signals induced by aparticles from the Pu source positioned before the Al foil. E Spectra of amplitudes of signals induced by protons under the variable intensity. A sample of an amplitude spectrum of one of the measured output pulses obtained from the MCP chevron setup is represented below (Fig. 6). Tests have shown that the UHF performance of the FMD-MCP setups is achieved: the signal duration for the given FMD-MCP test structure was obtained to be about 2 ns and the signal rise time is
X. SPECIAL DETECTORS
658
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
Fig. 5. The principal scheme of the scaling module that provides the 1 : 1024 dumping of the counting rate at high intensities amplitude spectra monitoring.
Fig. 6. Spectrum shape of signals from the FMD-MCP prototype induced by a-particles from the Pu a-source
better than 500—700 ps. Proton spectra were normalised to charged particles beam integrator counts used for measurements of the intensity of the primary proton beam. The first studies of the gain stability versus protons rate showed that for the given type of MCPs (500 M)) one can get 1.5;10 counts/s for 1 cm FMD-MCP pad anode for 50%
gain decrease. These studies are to be continued with the application of another type of MCPs (in particular with 70 M) resistance and a relevant faster channel recovery time). Further in-beam tests are also planned for the sector FMD-MCP prototypes to measure the multiplicity and the time resolution using the available beams.
A.E. Antropov et al./Nucl. Instr. and Meth. in Phys. Res. A 419 (1998) 654—659
5. Conclusions E Technical design and technology were developed for manufacturing a FMD-MCP prototype satisfying all requirements of UHV and UHF applications. E The first results obtained in long-term studies for the indpendent Ti-getter micro pump placed inside the 1 l volume during 240 days are very promising. (The pressure is being kept at better than 10\ Torr.) E In-beam tests of the small-area prototypes were started at the university cyclotron with controllable intensities of incoming particles (up to 10 particles/s). E Further in-beam tests are planned for the sector FMD-MCP prototypes to measure the multiplicity and the time resolution.
Acknowledgements Authors are indebted to J. Schukraft, O. Villalobos-Bailie and V. Lenti for useful discussions. This project is supported by the International Science and Technology Center, Grant No.345.
References
659
[2] N. Ahmad et al., ALICE technical proposal, CERN/ LHCC/95-71, LHCC/P3, Chs. 7 and 9, 15 December 1995. [3] G. Feofilov, T. Tulina, E. Zabrodin, Model simulations of the TOF spectra and timing resolution of the FMD, Internal Note ALICE/FMD, 1997. [4] R. Brockmann, Proc. Conf. of Physics and Astrophysics of Quark—Gluon Plasma, World Scientific, Singapore, 1988, pp. 617-623. [5] T.F. Gunzel et al., A silicon pad counter for first level triggering in ultrarelativistic proton—nucleus and nucleus—nucleus collisions, Preprint HD-PY-91/6, 20 November 1991. [6] B. Alessandro et al., Nucl. Instr. and Meth. A 360 (1995) 189. [7] L.G. Efimov et al., Fast ALICE L0 Trigger, Proc. 2nd Workshop on Electronics for LHC Experiments, Balatonfured, 23—27 September 1996, CERN/LHCC/96-39, p. 166. [8] L.G. Efimov et al., Fast front-end L0 trigger electronics for ALICE FMD-MCP: tests and performance, Proc. 3rd Workshop on Electronics for LHC Experiments, London, 22—26 September, 1997, CERN/LHCC/97-80, 21 October 1997, p. 359. [9] A. Kolozhvari, T. Tulina, F. Valiev, Determination of multiplicity with microchannel plate detector at the LHC. statistical approach, ALICE/93-15, Internal Note/MCP, 30 January 1993. [10] M.P. Larin, Preparation of thin film coatings allowing 10 reduction in gas emission on the surfaces of ultra-high vacuum systems, Proc. VUOTO Conf., vol XX, (N2), Aprile-Giugno, 1990, p. 310. [11] Surface Analysis System LAS Series, RIBER SA. B 268E 7/80. [12] P. Giubellino et al., Nucl. Instr. and Meth. A 279 (1989) 259.
[1] N. Antoniou et al., Letter of intent for a large ion collider experiment, CERN/LHCC/93-16,LHCC/I 4,1 March 1993.
X. SPECIAL DETECTORS