Maximum trapping energy at various L-shells for protons in the inner radiation belt of the Earth

The results of observation of high-energy trapped proton fluxes in the inner radiation belt of the Earth, obtained with the ARINA and the PAMELA magnetic spectrometers, are presented. The energy spectrum of protons has been continuously measured (2006 - 2016) in two complementary energy ranges: 40 - 110 MeV and >80 MeV, respectively. The two detectors were installed on board the Resurs-DK1 Russian satellite (350-600 km orbit altitude and 70 degrees inclination). The PAMELA acceptance pointed to zenith, while the ARINA viewing direction was perpendicular to the orbital plane of the satellite. These instrument orientations allowed to measure the particle fluxes with pitch-angles close to 90 degrees in a wide interval of L-shells, limited to <1.2-1.3 Re and 1.0-3.0 Re, respectively. It will be shown that maximum energy of trapped protons is defined by the adiabatic motion of particles in the geomagnetic field, increasing with decreasing L values, up to about 2 GeV at L=1.12 Re. Furthermore a weak dependence on the level of solar activity has been reported.