The SEPAGE diagnostic will detect charged particles (electrons, protons, and ions) accelerated in the interaction of the PETAL (PETawatt Aquitaine Laser) laser with its targets on the LMJ (Laser MegaJoule)-PETAL laser facility. SEPAGE will be equipped with a proton-radiography front detector and two Thomson parabolas (TP), corresponding to different ranges of the particle energy spectra: Above 0.1 MeV for electrons and protons in the low-energy channel, with a separation capability between protons and 12C6+ up to 20 MeV proton energy and above 8 MeV for the high-energy channel, with a separation capability between protons and 12C6+ up to 200 MeV proton kinetic energy. This paper presents the calibration of the SEPAGE's low-energy channel TP at the Tandem facility of Orsay (France) with proton beams between 3 and 22 MeV and carbon-ion beams from 5.8 to 84 MeV. The magnetic and electric fields' integrals were determined with an accuracy of 10-3 by combining the deflections measured at different energies with different target thicknesses and materials, providing different in-target energy losses of the beam particles and hence different detected energies for given beam energies.