CALET: A stopover at CERN before flying to space

The CALorimetric Electron Telescope (CALET) will be flying to the ISS this year. Calibration tests are currently being completed on a replica of the instrument at CERN’s H8 beam line. The final payload will then be transported on board a Japanese transfer vehicle and docked on the JEM-EF platform to take data and explore the high-energy cosmos.

The CALET calorimeter is preparing for installation in the flight module that will bring it to its final destination on the ISS.

The CALET calorimeter is preparing for installation in the flight module that will bring it to its final destination on the ISS (Image: JAXA/IA)

The detector was designed by a Japanese-led international collaboration to identify cosmic electrons, nuclei and gamma rays and to provide high-resolution measurements of their energy. Using two calorimetric instruments and a particle identification system, CALET will perform high-precision measurements of the electron energy spectrum from 1 GeV to 20 TeV. “By detecting electrons with an energy above 1 TeV, CALET might be able to identify the astronomical sources from which they originate,” says Shoji Torii of Waseda University in Tokyo, principal investigator of CALET. “There are currently many candidates but there is no experimental confirmation yet.”

The energy spectrum of the high-energy electrons could also reveal signatures of dark matter. “According to several dark matter theoretical models, the shape of the spectrum could be linked to the nature of dark matter,” says Pier Simone Marrocchesi, co-principal investigator of the CALET collaboration and head of the Italian team involved in the experiment. “Thanks to CALET’s excellent energy resolution and ability to distinguish between hadrons and electrons, and between charged particles and gamma rays, we are confident that CALET will contribute to shed light on these outstanding questions.”

CALET builds on the data from other space-based experiments, including Fermi, PAMELA, AMS, balloon instruments and ground-based Atmospheric Cherenkov Telescopes (ACT). Since its uniqueness resides in its ability to measure the energy of impinging cosmic particles, the energy calibration of the two calorimetric instruments is the key to the whole experiment. This is why calibration tests are being performed on a replica of CALET – basically, this is the same instrument except for some flight related control systems – installed at the H8 SPS beam line in the North Area at CERN's Prévessin site. “CERN offers us a unique opportunity to use high-energy beams of relativistic ions,” says Marrocchesi. “Even if the maximum beam energy during the current test at CERN is limited to 150 GeV/n for elements from deuterium to argon while once in space we want to detect higher-energy particles, these measurements will provide us with the necessary information on how our detector works.”

After the calibration tests, the focus will move to Japan where the Japanese Aero-Space Agency (JAXA) is finalising the preparation of the H-II transfer vehicle (HTV) that will fly CALET to the ISS. A robotic arm on the ISS will then position the instrument on the external platform of the Japanese module (KIBO). CALET is expected to take data for about five years.