Takizawa, Y

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29th International Cosmic Ray Conference Pune (2005) 8, 213216Development of Elementary Cell module for the EUSO Focal SurfaceDetectorY. Takizawa , Y. kawasaki , M. Sato , M.E. Bertaina , T. Ebisuzaki , H. M. Shimizu , T.Sawabe, F. Kajino, I. Sato, H. Takara, N. Isono, M. Ameri, S. Cuneo, F. Fontanelli,V. Gracco, P. Musico, M. Pallavicini, A. Petrolini, M. Sannino, F. Siccardi, A. Theaand EUSO Collaboration(a) RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan(b) Department of Physics, Konan University, Kobe 658-8501, Japan(c) Meisei Electric Co,Ltd, 2-5-7, Koishikawa, Bunkyo-Ku, Tokyo 112-8511, Japan(d) Dipartimento di Fisica dell’Universita and INFN, 16146 Genova, ItalyPresenter: Y. Takizawa (takky@riken.jp), jap-takizawa-Y-abs1-he15-posterThe Focal Surface detector of EUSO (Extreme Universe Space Observatory) consists of small autonomousfunctional units (elementary cell, EC) assembled in larger modules (Photo Detector Modules, PDM). Each ECis conceived as an array of 4 multianode photomultipliers (MAPMTs). We have developed EC structure for thecurrent baseline of the multianode photomultiplier (MAPMT, R8900-M36). As the mechanical characteristicsof the PDM structure (e.g. robustness to thermal and launch shocks, vibrations at launch) will affect the ECstructure, we have also built a trial PDM, consisting of 36 MAPMTs (9 ECs) arranged in a cartesian layout.The purpose of such trial PDM is to develop and optimize the EC structure.1. IntroductionEUSO is a science mission to detect Extremely High Energy Cosmic Rays at energies E  10eV. It is asuper wide-field telescope that observes UV photons from air showers produced by cosmic rays in the nightside of the Earth. EUSO will be attached to the Columbus module of the International Space Station (ISS).EUSO is a collaborative effort among scientists of Europe, USA, and Japan. The phase-A study (conceptualdesign) under ESA has been successfully finished in July 2004[1] and the international negotiations for phase-B (detailed design) are in progress. The EUSO telescope, which diameter is 2.5m, comprises of a pair ofdouble-sided curved Fresnel lenses with a curved focal surface and the electronics. Its field of view is 60  withf/# = 1.25 and the angular resolution of the optics is at the order of 0.1  in Phase-A baseline design.2. The focal surface detectorThe focal surface detector is a closely packed mosaic of MAPMTs approximating the curved focal surface.Near-ultraviolet photons (300 nm 	 400 nm) are selectively delivered onto the focal surface detector by em-ploying optical filters on top of the detector. Hamamatsu R7600 series MAPMT with UV-glass entrance win-dows had been indicated as baseline photo-detector at the beginning of Phase-A. However, these types ofMAPMT have a large dead area and the sensitive area ratio is only about 45%. The Japan team has developeda new type of MAPMT, Hamamatsu R8900 series, to enlarge the sensitive area ratio of the MAPMT. R8900series are modified from R7600 series by introducing a grid between the photocathode and the first dynode toelectrostatically demagnify the photoelectron image onto the dynode[2]. The average sensitive area increasesup to 83% of its physical dimension. The small dead area can be removed rather easily. One possible methodis to employ a tapered light guide on top of the MAPMT. An example is shown in Figure 1. An estimationobtained using the tapered BG-3 filter gives a sensitive area ratio higher than 93% over the whole elementarycell (EC), which is described in the next section. The entire pixel array on the focal surface will be configured214 Y. Takizawa et alas an array of clustered pixels. The schematic of the focal surface is shown in Figure 2. We refer to the pixelcluster as the Photo Detector Module (PDM). The PDM size will be chosen so that most of the air showertracks will be fully contained in one PDM.Figure 1. Tapered lightguide on the top of mul-tianode photomultiplier.Figure 2. The focal surface detector conguration.3. Development of the Elementary-CellBy the Phase-A definition, ”Each elementary-cell contains four units of MAPMT R8900, additional opticaladapters to increase the its physical detection area, HV/LV power connectors, one HV voltage divider forany of the MAPMT units, common heat dissipation facilities, common miscellaneous services and monitoringdevices, all of the Front-End electronics plus as much as possible of the trigger/read-out electronics integratedin the EC and connectors for signal transmission and control lines.”INFN team has developed successfully the EC Prototype by using R7600 in the Phase-A work[3][1]. The fourMAPMT units are located on a base-board together with the passive electronics of the voltage dividers, andthe MAPMT can be inserted in the upper part of the socket. The lower part of the socket contains a ball gridarray (BGA) that is soldered to the EC board. INFN’s method will be suitable for the Flight model. As theadditional step, we are searching other possibility of EC design as a backup solution. So, Japan team andMeisei electric co.,ltd. are developing the EC module structure for the current base line R8900-M36 MAPMTunder the supervision of the INFN team. Additionally, we have developed the trial PDM, ”trial” means thisPDM is not prototype model, because it is necessary to know the characteristics of PDM to decide the structureof EC. The specifications of the EC and trial PDM are described in the followings and Figure 5:1. The four R8900-M36 MAPMT units are located on a EC board.2. The vibration tolerance level of EC is random 20 G rms, 120 sec, for X, Y and Z axis. A method of MAPMTmount is that MAPMT bottom surface touches EC base surface. Pins of MAPMT go through holes on the ECbase. This method staves off glass seals of pins being broken by vibration. See Figure 3.3. The distance of each optical adaptor’s top is 0.5 mm.4. EC has flexible readout cables to connect the PDM daughter circuit board. We selected the easy readoutmethod by using flexible cables connection, because the BGA connecting technique was established by Italianteam. The ASIC has to be as close as possible to the MAPMT, because we need a fast time response andthe connections have a non-negligible capacitance. So, The BGA connecting method will be suitable for theEUSO Flight model.5. The vibration tolerance level of trial PDM is random 20 G rms, 120 sec, for X, Y and Z axis.6. Trial PDM has 3  3 ECs (9ECs = 36 MAPMTs).Development of Elementary Cell ... 2157. Trial PDM has a HV supply circuit, which distributes to high voltage to 36 MAPMTs[4].8. Trial PDM has 3 daughter circuit board.9. A daughter board takes in 3 ECs, has 3 HV divider circuits and readout connecters. Each divider circuittakes in 1 EC (4 MAPMTs).Prototypes of the EC and trial PDM were built as shown in Figure 4 and Figure 6. We will test these perfor-mance in the FY 2005. The overall vibration test was done on 20 June, 2005. EC and trial PDM survived fromrandom 20 G rms vibration test, 120 sec, for X, Y and Z axis.Figure 3. How to x MAPMT on the EC base. MAPMTbottom surface touches EC base surface to withstand random20 G rms vibration level.Figure 4. EC and exible read out cables.Figure 5. Schematic picture of Trial PDM module and EC designFigure 6. Trial X-Y layout PDM4. ConclusionsWe have developed successfully EC prototype development by using R7600 in the Phase-A work. As supportedwork, we are developing the EC module structure for the current baseline R8900-M36 MAPMT and the trialPDM model. the EC and trial PDM survived from random 20 G rms vibration test, 120 sec, for X, Y and Z216 Y. Takizawa et alaxis. And furthermore, we will test (e.g. robustness to thermal and launch shocks) in the FY 2005. The resultswill be reflected in the Phase-B detail design.5. AcknowledgementsThis study is partially supported by the ” Grants-in-aid President’s Discretionary Fund” promoted by RIKEN.References[1] EUSO Collaboration, EUSO Report on the Phase A study (2004).http://www.euso-mission.org/.[2] Y. Kawasaki et al, This conference proceedings (2005).[3] M. Ameri et al, 28th ICRC proceedings,939-942 (2003).[4] F. Kajino et al, This conference proceedings (2005).

Development of Elementary Cell module for the EUSO Focal Surface Detector

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