The Telescope Array project is an international collaboration involving research and educational institutions in Japan, Taiwan, China, Russia, South Korea, and the United States. The experiment is designed to observe ultra-high-energy cosmic ray air showers using a combination of ground array and air-fluorescence techniques. It is located in the high desert in Millard County, Utah, USA at about 1400m above sea level.
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The TA observatory is a hybrid detector system consisting of both an array of 576 scintillation surface detectors which measure the distribution of charged particles at the Earth's surface, and three fluorescence stations which observe the night sky above the SD array.[1] Each fluorescence station is also accompanied by a LIDAR system for atmospheric monitoring.[2] The SD array is much like that of the AGASA group, but covers an area that is nine times larger. The hybrid setup of the Telescope Array project allows for simultaneous observation of both the longitudinal development and the lateral distribution of the air showers.
At the center of the ground array is the Central Laser Facility which is used for atmospheric monitoring and calibrations.
The Lon and Mary Watson Millard County Cosmic Ray Center was dedicated on March 20, 2006.[3] The center is located in Delta - the seat of Millard County. The building serves as a headquarters and data processing center for the TA Project.
The surface detectors are evenly distributed across a 762 km2 grid array with 1.2 km between each unit. Each surface detector has an assembled weight of 250 kg and consists of a power supply, two layers of scintillation detectors and electronics. Power is generated by a 120W solar panel and stored in a sealed lead-acid battery. The system has the capacity to operate for one week in complete darkness. Each scintillation detector layer is made of extruded plastic scintillator that is 1.2 cm thick and has an area of 3m2. The photo multiplier tube is connected to the scintillator via 96 wave length shifting fibers.
The Telescope Array has three fluorescence detector stations. The stations are located on a triangle about 35 km apart from one another. Each station has 12-14 telescopes viewing the range from 3 to 33 degrees in elevation. The three sites are named Black Rock Mesa (BRM), Long Ridge (LR), and Middle Drum (MD).[4]
Each telescope has a fluorescence light camera made up of 256 PMTs.
TALE is the Telescope Array Low Energy extension. It is designed to observe cosmic rays with energies between 3x1016eV and 1019eV. TALE has two fluorescence sites, one of which is located about 5 km away from the Black Rock Mesa FD site, and another which is about 5 km away from the Long Ridge FD site.[5]
The TALE tower is a tower of fluorescence telescopes looking from near zenith to near horizon. These telescopes have 3m diameter mirrors to push the energy threshold of observable events as low as possible.
The TALE project also has an infill array of scintillator ground array stations spaced about 500m apart. These stations measure charged particle densities (the shower footprint) at the Earth's surface for lower energy events approaching 3x1016eV