FT-ICR studies of high mass (C\sb>150) carbon clusters have brought insight to the controversial structures of carbon fullerenes. Laser vaporization followed by supersonic beam technique produced carbon clusters that directly injected into the bore tube of a 6 Tesla magnet. Mass spectra of the trapped cluster ions reveal the presence of only even-numbered clusters in the low mass regions, thus verifying the predominance of graphite closed shells. It is believed that the larger clusters also exist as aggregates loosely bound to each other on their surfaces and will readily disaggregate upon evaporation. When clusters of size C\sb300 or larger are fragmented by excimer laser, the products are mostly even-numbered ions resulting from C\sb2 loss which satisfy the retention of a fullerenes structure. In addition, there are distributions of multiply-charged high mass positive clusters detected as the photofragments undergo thermionic emission. This fragmentation experiment is currently used to compare the hypotheses of (1) giant fullerenes model where carbon condenses to form empty hollow cages of large radii, (2) aggregation of small clusters by van der Waals forces to form high mass clusters, and (3) "Russian-egg" model where high mass clusters exist as concentric closed shells.