The thermalization of fast moving ions plays a pivotal role in the ability of projectile fragmentation facilities such as the National Superconducting Cyclotron Laboratory (NSCL) to provide experimenters with low-energy ion beams for precision experiments. The NSCL produces radioactive ion beams (RIBs) with kinetic energies of the order ~100 MeV/u and velocities of up to half the speed of light. More than ten years ago, the NSCL first proposed and demonstrated a beam thermalization technique for projectile fragments. In order to provide beams with energies on the order of ~10 keV, the fast RIBs first pass through a dispersive ion-optical system, solid degraders, and then a monoenergetic wedge to remove the bulk of their kinetic energy. The remaining kinetic energy of ~1 MeV/u is then dissipated through collisions with the buffer gas atoms in a large volume linear gas cell. The original NSCL gas cell was compact (5 cm wide x 50 cm long), ran at a high pressure (760 torr), and used a DC drag field and gas flow to guide and extract the ions. The new, large volume linear gas cell constructed by Argonne National Lab (ANL), is larger (25 cm x 120 cm), operates at medium pressures (55 to 100 torr), and employs an elaborate electrode structure with both static and dynamic electric fields as well as gas flow to guide and to extract the thermalized ions. The present work describes a series of commissioning experiments for the NSCL's large volume linear gas cell that were conducted using 76Ga beams produced at approximately 90 MeV/u in the A1900. Since the commissioning experiments, numerous additional ion beams have been thermalized and extracted from this gas cell, and some of the results are also presented here. The fast beams were delivered to the large volume linear gas cell in a new momentum compression beam line, and the range distributions, extraction efficiency, and the overall efficiency of the system were measured as a function of the incident intensity. The data from the commissioning runs were compared to predictions from the stopping and range of ions in matter (SRIM) code and the LISE++ code. Particle-in-cell (PIC) calculations were carried out to evaluate the space charge produced by the stopping of the energetic fragments, and finally, SIMION calculations of the ion migration in the gas cell were performed to evaluate the effectiveness of the changes and upgrades from the previous cell. Results from these studies revealed that the larger size, upgraded electrode structure, and additional dynamic potential on the walls and cone of the NSCL's large volume linear gas cell did, in fact, improve the extraction efficiency of the system when compared to previous generation devices.
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