We report the observation of the first ten collective parametric reson
ances of an uncooled N-2(+) ion cloud in a Paul trap driven at simple
fractions of twice the secular frequency of the trap by an additionall
y applied quadrupole field. The fractional resonances are observable o
nly if the excitation field surpasses a critical strength. Odd-even st
aggering of the thresholds is observed.