The PAMELA experiment was part of the Russian Italian Mission (RIM) program, which included several space missions with different scientific programs. The RIM-1 experiment studied the isotopic composition of cosmic nuclei by means of the silicon telescope NINA carried by the russian polar orbit satellite Resource-04. The NINA instrument was launched successfully from Bajkonur on July 10th, 1998 and had been taking data for about an year. The RIM-2 mission was the PAMELA experiment while the RIM-3 project, called GILDA, was proposed to study high energy cosmic gamma rays.
The PAMELA apparatus, installed on-board of the Russian Resource-DK1 satellite, was launched on June, 15 2006. The sun-synchronous, 680 km polar orbit allowed studying the low energy cosmic rays, close to the poles. The main scientific objectives of the experiment were the precise measurement of the cosmic-ray composition and energy spectra with a focus on the positron and antiproton fluxes at energies from 100 MeV to above 100 GeV, as well as the search for antihelium with a sensitivity of 10-7 in the antiHe/He ratio.
Initially planned for three years, PAMELA operation lasted until January 2016 when the data transmission from the satellite to the ground station in Moscow was interrupted because of technical problems with the satellite. The experiment, making long duration measurements of the cosmic radiation over an extended energy range, represented a major step forward in cosmic-ray studies providing an order of magnitude improvement in statistics respect to previous experimental data. Especially significant have been the results obtained by the PAMELA experiment concerning antiparticles such as antiprotons and positrons. Together the antiproton and positron results have been cited by more than 2000 other papers and hundreds of theoretical works have been put forward to explain the results. Furthermore, data concerning cosmic-ray acceleration and propagation mechanisms, solar modulation, solar flares and Earth’s Magnetosphere have generated a significant amount of theoretical work. For example, in 2011 the PAMELA collaboration published in “Science” new results on the cosmic-ray proton and helium spectra that challenged the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy.
The PAMELA apparatus, shown below, has an overall height of about 1.2 m and consists of:
- a spectrometer based on a permanent magnet equipped with a silicon microstrip tracker to measure particle tracks and momenta;
- an imaging calorimeter, which was responsibility of our group;
- a Time of Flight (TOF) and first level trigger system based on plastic scintillators;
- an anticoincidence system , also based on plastic scintillators;
- a scintillator tail catcher;
- a neutron detector.