0000000000352134
AUTHOR
Reinhold Blümel
Fractional frequency collective parametric resonances of an ion cloud in a Paul trap
ion cloud ina Paul trap driven at simple fractions of twice the secular frequency of the trap by an additionally appliedquadrupole field. The fractional resonances are observable only if the excitation field surpasses a criticalstrength. Odd-even staggering of the thresholds is observed.@S1050-2947~98!51307-8#PACS number~s!: 32.80.Pj, 07.75.1h
Nonlinear collective oscillations of an ion cloud in a Paul trap
In an experiment using a Paul trap, we create a ${\mathrm{H}}_{2}^{+}$ ion cloud by electron ionization of the background gas at ${10}^{\ensuremath{-}9}$-mbar residual pressure. Exciting the ions parametrically at twice the frequency of the secular motion of ions in the $r$ or $z$ direction, we observe a narrow resonance at some distance from the motional resonance center if the amplitude of the exciting field exceeds a threshold value. The threshold value decreases with increasing ion number. Since the narrow resonance does not shift with ion number, we interpret it as a collective resonance of the center of mass of the ion cloud. The resonance shape exhibits the typical form of a driven a…