Individual and center-of-mass resonances in the motional spectrum of an electron cloud in a Penning trap P. Paasche, T. Valenzuela, D. Biswas, C. Angelescu and G. Werth Eur. Phys. J. D, 18 3 (2002) 295-300 Published online: 15 March 2002 DOI: 10.1140/epjd/e20020033