29th International Cosmic Ray Conference Pune (2005) 00, 101-104

Telescope Array; Progress of Surface Array
H.Kawaia, T.Nunomuraa, N.Sakuraia, S.Yoshidaa, H.Yoshiib, K.Tanakac, F.Cohend,M.Fukushimad, N.Hayashidad, M.Ohnishid, H.Ohokad, S.Ozawad, H.Sagawad, T.Shibatad,
H.Shimodairad, M.Takedad, A.Taketad, M.Takitad, H.Tokunod, R.Toriid, S.Udod, H.Fujiie,T.Matsudae, M.Tanakae, H.Yamaokae, K.Hibinof, T.Bennog, M.Chikawag, T.Nakamurah,
M.Teshimai, K.Kadotaj, Y.Uchihorik, Y.Hayashil, S.Kawakamil, K.Matsumotol,
Y.Matsumotol, T.Matsuyamal, S.Ogiol, A.Ohshimal, T.Okudal, D.R.Bergmannm,
G.B.Thomsonm, N.Inouen, Y.Wadan, K.Kasaharao, J.W.Belzp, M.Fukudaq, T.Iguchiq,
F.Kakimotoq, R.Minagawaq, Y.Tamedaq, Y.Tsunesadaq, J.A.J.Matthewsr, T.Abu-Zayyads,
R.Cadys, Z.Caos, P.Huentemeyers, C.C.H.Juis, K.Martenss, J.N.Matthewss, J.D.Smiths,P.Sokolskys, R.W.Springers, S.B.Thomass, L.R.Wienckes, T.Doylet, M.J.Taylort,
V.B.Wickwart, T.D.Wilkersont, K.Hashimotou, K.Hondau, T.Ishiiu, T.Kanbeu(a) Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi, Chiba, 263-8522 Japan(b) Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan(c) Hiroshima City University, 3-4-1 Ozuka-Higashi, Asa-Minami-Ku, Hiroshima, 731-3194 Japan(d) ICRR, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8582 Japan(e) Institute of Particle and Nuclear Studies, KEK, 1-1 Oho, Tsukuba, Ibaraki, 305-0801 Japan(f) Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa, 221-8686 Japan(g) Kinki University, 3-4-1 Kowakae, Higashi-Osaka City, 577-8502 Japan(h) Kochi University, 2-5-1 Akebonocho, Kochi, 780-8520 Japan(i) Max-Planck-Institute for Physics, Foehringer Ring 6, 80805 Muenchen, Germany(j) Musashi Institute of Technology, 3-3-1 Ushikubo-Nishi, Tsuzuki-ku, Yokohama, Kanagawa, 224-0015 Japan(k) National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba-shi, 263-8555 Japan(l) Osaka City University, 3-3-138 Sugimotocho, Sumiyoshi-ku, Osaka, 558-8585 Japan(m) Rutgers University, 136 Felinghuysen Road, Piscataway, NJ 08854, USA(n) Saitama University, 255 Shimo-Okubo, Saitama, 338-8570 Japan(o) Shibaura Institute of Technology, 307 Fukasaku, Minuma-ku, Saitama, 337-8570 Japan(p) Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550 Japan(q) University of Montana , 32 Campus Drive, Missoula, MT 59812, USA(r) University of New Mexico, Albuquerque, NM 87131 USA(s) University of Utah, 115 S 1400 E, Salt Lake City, UT 84112, USA(t) Utah State University, Logan UT 84322, USA(u) Yamanashi University,4-4-37 Takeda, Kofu, Yamanashi, 400-8510 Japan

Presenter: H.Sagawa (hsagawa@icrr.u-tokyo.ac.jp), jap-sagawa-H-abs1-HE15-oral
The telescope Array (TA) experiment, currently under construction in Utah, USA, is an array of surface
detectors with air fluorescence telescopes to study the highest energy cosmic rays of energy beyond 1020eV.
The TA surface detector array will consist of 576 plastic scintillation counters, on a square grid with 1.2 km
spacing, covering the ground area of 760 km2. Each surface detector is outfitted with two layers of
scintillators of 3m2 area, readout electronics, and wireless LAN communication system, which are poweredby solar system. The test of an Engineering Array with 18 surface detectors is currently operating after being
deployed in December 2004. Here we present the design and the progress of the surface detectors of TA,
focusing on the status of the Engineering Array.

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1. Introduction
The purpose of the TA experiment is to measure the cosmic ray spectrum in the GZK cutoff region
decisively and to pin down the nature of cosmic rays exceeding 1020 eV. The surface detector consists of anarray of 576 plastic scintillators deployed in a grid of 1.2 km spacing covering the ground area of ~760 km2.
For energies greater than 1020eV, more than 90% of the primary energy is transferred to the electroniccomponent (e+, e－and γ) at the end of the shower development. The plastic scintillator is sensitive to thecharged particles in the air shower and the energy measurement is less affected by the difference of the detailof unknown hadronic interactions and the primary composition.. The detector acceptance is approximately 9times that of AGASA. The detector efficiency is 100% for cosmic rays with energies more than 1019.5 eVentering the detector with zenith angles less than 45o.

2. Apparatus of Surface Detector
Each detector consists of plastic scintillators, photomultipliers (PMTs), wave length shifter fibers,
electronics system, a communication system, and a solar power system. A simple and robust counter design
will make the system easy to deploy and maintain in the desert.
We install wave length shifter fibers of 1 mm diameter in the grooves at 2 cm interval on the surface of thescintillator compouned by C.I. Industry Inc. Scintillation counter consists of two layers of plastic scintillatorof 1.2 cm thickness with the area of 3 m2. Scintillation light is read out by a separate PMT (Electrontubes9124SA), each connected to the edge of the bundle of fibers on each scintillator layer. A coincidence istaken between 2 layers for obtaining a stable trigger condition against environmental background and PMT
noise. Please refer to [1] and [2] for an explanation of the performance of the surface scintillation detector
and PMT for the TA experiment.
Signals from PMTs will be continuously digitized with a 12-bit flash ADC with 50 MHz sampling. For aPMT signal exceeding 1/3 of the muon peak, a complete wave form of ~4µs is stored locally in a memory
with a time stamp supplied by the Global Positioning System (GPS). We chose Motorola M12+ Timing
Oncore Receiver. The rate of local buffering is expected to be less than 1 kHz for the 3 m2 counter. The
relative timing between remotely separated counters should be maintained within 20 ns by the GPS for thegood resolution of arrival direction. A list of triggered events containing the pulse height and timing
information of the hits is sent to a central DAQ system every second. If a trigger condition of 3 or moremuons is adopted, the trigger list would contain ~100 events. An air shower event is identified by the central
DAQ software by requiring clustered hits of counters with a good timing of coincidence. The air shower
event rate will be significantly less than 1 Hz when we require at least 3 counters are hit at the same time.
The data acquisition system will be composed of a wireless local area network (LAN) using 2.4 GHz spread
spectrum technology. Considering a limited reach of the presently available models, two stages of data
concentration will be necessary to reach the central DAQ from individual counters. The speed of less than 1
Mbps is, however, sufficient for the expected trigger rate and DAQ throughput even when 2 or more stagesof data collection are necessary. Five communication towers would be needed: three for nearby telescope
stations and two for the places where communication may be difficult by only three towers. More details ontrigger and data acquisition electronics are found in reference [3].
The total electrical power consumed by PMT, ADC, GPS and wireless LAN will be of ~5W. It is locallygenerated by one solar panel of ~120W and stored in one lead acid battery of 100 Ah for deep cycle
applications and supplied through a charge controller.

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To check the stability and detection efficiency, we monitor single muon peak and the trigger rate. For thequick check of dynamic range and linearity, we attach two LEDs (NSPB320BS made by NICHIA Corp.) toeach layer.
Scintillator platforms are to be constructed of 2 inch square tubular steel legs and frame. Scintillators withfibers and PMTs will be contained in a 2.3m x 1.7 m x 10cm high stainless steel box, which lies on top of
the platform and is covered with a thin steel roof in order to avoid sunlight and rain. The solar panel isinstalled on top of the platform at a 60 degree angle. Behind and below the solar panel will be a metal
enclosure containing the storage battery and electronics boards. A lightweight 10 ft. antenna would be
attached to each platform. The over-all dimensions of each detector is 7 ft. wid, 12 ft. long, and 6 ft hight(not including the antenna).

Figure 1. A scintillation surface detector deployed in the field for the Engineering Array test.

3. An Engineering Array Test and Prospects
On December in 2004, 18 scintillation surface detectors were placed as an engineering array. The purpose isto test the deployment and technical designs. Figure 2 shows the location of 18 detectors and the single
temporary communication tower. The detectors were assembled in Delta City near the site. All the detectorswere moved by trucks first to the staging area which is located alongside of an existing road. Each detector
was picked up from there by helicopter and taken to the position to be deployed. Data transfer is successful
between the detector and the temporary communication tower. The wave form distributions of signals fromtwo PMTs by cosmic rays are successfully recorded through wireless LAN communication system as shownin Figure 3. Based on the engineering array and the basic performance test, we chose Sharp solar panel NDL3EJE, DYNASTY battery DCS-100L, and decided to produce homemade charge controller for solarsystem. The electronics are being revised to the final version for mass production. We started mass assemblyof scintillators in Japan and mass production of the platforms in Utah. We purchased or started purchasing
commercial products such as PMTs, solar panels, batteries, and GPS. The mass deployment of the detectors
will begin late in 2005. The surface detectors will be completed and operational by the spring of 2007.

4. Conclusions
On December in 2004, 18 scintillation surface detectors were deployed as an engineering array. Data transfer
is successful between the detector and the communication tower, and the wave form distributions of signals

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by cosmic rays are successfully recorded. We started mass production of the detectors. The mass deploymentof the detectors will begin late in 2005 and will be completed by the spring of 2007.

Figure 2. Location of the Engineering Array of surface detectors. 18 detectors and single temporary communication
tower are shown as blue dots.

Figure 3. The wave form distributions of signals from two PMTs of the scintillator detector by a cosmic ray.

5. Acknowledgements
The discussion with colleagues in AGASA, HiRes and TA collaborations is highly appreciated. TheTelescope Array is being constructed by the support of Grant-in-Aid for Scientific Research (Kakenhi) on
the Priority Area "The Highest Energy Cosmic Rays" by the Ministry of Education, Culture, Sports, Scienceand Technology of Japan.

References[1] S. Kawakami for the Telescope Array experiment, these proceedings[2] S. Yoshida for the Telescope Array experiment, these proceedings[3] S. Ozawa for the Telescope Array experiment, these proceedings