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The Telescope Array project is a collaboration between universities and institutions in the United States, Japan, Korea, Russia, and Belgium. The experiment is designed to observe air showers induced by cosmic rays with extremely high energy. It does this using a combination of ground array and air-fluorescence techniques. The array of scintillator surface detectors samples the footprint of the air shower when it reaches the Earth's surface, while the fluorescence telescopes measure the scintillation light generated as the shower passes through the gas of the atmosphere.

The Telescope Array observes cosmic rays with energies greater than 10¹⁸eV. The surface array samples events over 300 square miles of desert. It consists of more than 500 scintillator detectors, each 3 m² located on a 1.2 km (3/4 mile) square grid. In addition, there are three telescope stations on a 30 km triangle. They are instrumented with 12-14 telescopes each. The Telescope Array has been collecting data in the high desert in Millard County, Utah, USA since 2007.

We are currently adding a low energy extension to the Telescope Array which will enable us to study the changes in the energy spectrum and chemical composition over a broader energy range. TALE (the Telescope Array Low Energy extension) will allow the observation of cosmic rays with energies as low as 3x10¹⁶ eV. This is accomplished by adding 10 new high elevation angle telescopes, viewing up to 72°, to one of the telescope stations and adding a graded infill array of scintillator surface detectors.

The higher observation angles are required to view the full development of the air showers since lower energy showers develop higher in the atmosphere. The more densely spaced surface array is necessary since the footprint of lower energy showers is smaller and they could be missed between the more broadly spaced detectors. Finally, the dense surface array must reach close to the telescope station with the high elevation telescopes since the low energy showers will produce less light and we will want to observe the showers with both sets of detectors.

For more information about TALE see the TALE Program Overview.