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 30 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-Size Telescopes (MSTs). Eight Large-Size Telescopes (LSTs) and 70 Small-Size Telescopes (SSTs) are planned to extend the energy range below 100 GeV and above 10 TeV.

From Left: Three different SST prototype designs, the MST prototype design and the LST prototype design.

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.


The final arrays will combine LSTs, MSTs (and perhaps Schwarzschild Couder Telescopes) and a mixture of SST designs.


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.


Telescope Prototype Construction Webcams


Prototypes exist for all of the proposed telescope designs except for the LST and SCT, which are under construction. Watch their progress live on their respective construction webcams (LST construction in La Palma on left; SCT construction in Arizona on right):