Electron-radiation interaction in a Penning trap: beyond the dipole   approximation
  We investigate the physics of a single trapped electron interacting with a radiation field without the dipole approximation. This gives new physical insights in the so-called geonium theory. 
Ana M. Martins (Instituto Superior Tecnico, Lisboa, Portugal), Stefano   Mancini and Paolo Tombesi (Dpt. Matematica e Fisica...