Abstract
A nitrogen cluster beam (neutral particle intensity of 28.6 mAeq) is ionized by electron collisions in a Bayard-Alpert gauge type ionizer. The extraction efficiency of about 65% is obtained at an electron current of 10 mA with an energy of 50 eV. The mean cluster size produced at a pressure of 663 Torr and temperature of 77.3 K is 2×105 molecules per cluster. By the Coulomb repulsion force, multiply ionized cluster ions are broken up into smaller fragments and the cluster ion size reduces to one-fourth at an electron current of 15 mA. Mean neutral cluster sizes depend strongly on the initial degree of saturation Φ0 and are 2×105, 7×104 and 3×104 molecules per cluster at Φ0's of 0.87, 0.66 and 0.39, respectively.
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