The technology behind the next generation very-high energy gamma-ray detector

»CTA's three classes of telescope will provide a broad energy coverage from billions to trillions the energy of visible light.«

CTA Technology

CTA is the next generation ground-based observatory for gamma-ray astronomy at very-high energies in the range from 20 GeV to 300 TeV. CTA’s detection of high-energy gamma rays is based on the imaging air Cherenkov technique (see How CTA Works). Three classes of telescope types are required to cover the full CTA energy range (20 GeV to 300 TeV). For its core energy range (100 GeV to 10 TeV), CTA is planning 40 Medium-Sized Telescopes (MSTs). Eight Large-Sized Telescopes (LSTs) and 70 Small-Sized Telescopes (SSTs) are planned to extend the energy range below 100 GeV and above 10 TeV, respectively.

From Left: The SST prototype design, the two medium-sized prototype designs (SCT and MST) and the LST prototype design. Image credit: Gabriel Pérez Diaz, IAC.

The MSTs and LSTs will be installed on both sites, while the SSTs will only be installed on the southern hemisphere site. The below graphic illustrates the proposed layout for both sites:



Once the mirrors reflect the light, the CTA cameras capture and convert it into data. Each telescope has its own variation of camera, but the designs are all driven by the brightness and short duration of the Cherenkov light flash. A Cherenkov light flash lasts only a few billionths of a second and is extremely faint. The cameras are sensitive to these faint flashes and use extremely fast exposures to capture the light. Photomultiplier tubes (PMTs) or silicon photomultipliers (SiPMs) will convert the light into an electrical signal that is then digitised and transmitted.

Further Reading

Download the CTA Telescope Specifications (PDF / 176 KB)



Beyond performance specifications such as light collection power, point spread function (PSF), pixel size and field of view, emphasis is placed on improved reliability and good maintainability compared to current generations of telescopes. The below table includes the detailed specifications of the proposed telescopes as of December 2019:



CTA Performance


CTA will provide very wide energy range and excellent angular resolution and sensitivity in comparison to any existing gamma-ray detector. Energies up to 300 TeV will push CTA beyond the edge of the known electromagnetic spectrum, providing a completely new view of the sky. To learn more about CTA’s expected baseline performance based on detailed Monte Carlo simulations of the facility, go to the CTA Performance page.

Telescope Prototype Construction Webcams


Prototypes exist for all of the proposed telescope designs and are now undergoing testing before they are considered for acceptance by the CTA Observatory. Check out the LST in La Palma on the left and the SCT in Arizona on the right: