Correlated oscillations and their rf spectra detectabilities of two oppositely charged thermal ion clouds in a Paul trap

A symmetric expression is derived for the coulombic interaction between two species of thermal ions trapped in a r.f. trap. Consequently, the oscillation frequencies of the weak and the strong oscillation modes of the system and their relevant conditions are expressed quantitatively. When two kinds of oppositely charged ions are trapped, a strong coupling region near a strong correlation line always exists, so that the coupling type can be controlled by selecting a suitable operation point. The detectability and the evolution of the electrical signals by r.f. resonance absorption detection are also discussed.