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; G. Werth

doi:10.1140/epjd/e20020033

EPJ

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^a

Johannes Gutenberg University, Institut fuer Physik, 55099 Mainz, Germany

Received: 11 July 2001
Revised: 12 November 2001
Published online: 15 March 2002

Abstract

We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass resonance suggests that it is a parametric instability of a Mathieu type equation of motion.

PACS: 52.27.Jt – Nonneutral plasmas / 82.80.Qx – Ion cyclotron resonance mass spectrometry