HIGHER-ORDER NONLINEAR RESONANCES IN A PAUL TRAP

We report some detailed investigations on non-linear resonances of hig h order as they appear in a radio-frequency ion trap, whose potential deviates from the ideal quadrupolar shape. The strength and shape of t hese resonances have been measured throughout the first stable region of the trap. Moreover, space charge shifts and also effects of a modul ation of the trapping voltage on the shape of the resonances have been observed. Some of the resonances cannot be explained by the general r ule that the sums of multiples of the ion macrofrequencies n(r) omega( r) + n(z) omega(z) (n(r), n(z) are integers) are multiples of the trap ping held frequency Omega.