High energy refers to the energy imparted to particles, high intensity refers to the number of particles (presumably of the particle beams), at least if the terminology is anything similar to synchrotrons.
So a high intensity 3GeV beam would be one where the average particle energy is 3GeV, with a larger number of particles comprising the beam than a low/medium intensity one.
So a high intensity 3GeV beam would be one where the average particle energy is 3GeV, with a larger number of particles comprising the beam than a low/medium intensity one.