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Figure 2. Rapid conversion of an ultracold gas of Rydberg atoms into an ultracold plasma. The number of free ions is plotted as a function of time, starting with 3.3 x 105 Rydberg rubidium atoms in the n = 40 state. The Rydberg atoms are created at time t = 0 and slowly ionize until enough electrons are present for the avalanche to begin.