A high-power laser ablation ion source for Penning trap studies of rare isotopes.

摘要

A high-power laser ablation ion source has been developed, characterized and implemented as part of the Low Energy Beam and Ion Trap (LEBIT) experiment at the National Superconducting Cyclotron Laboratory. LEBIT was developed to make precision measurements of rare isotopes, including mass measurements with a Penning trap. The system relies on thermalizing nuclear reaction products in a helium-filled cell and then extracting them from the gas through ion-manipulation and differential pumping. Atomic ions and clusters are needed to calibrate various aspects of the entire system such as transport efficiency and the main magnetic field, in addition to understanding properties of the helium-filled gas cell. High-power laser ablation has proven to be a successful method for producing a wide range of ions under various conditions, including atmospheric pressure. Laser ablation studies of C, Al, Ag, Au, Cu, Fe, and Zn were carried out in two separate chambers, one under vacuum conditions and one under buffer gas conditions, with the second harmonic, 532 nm, from a Q-switched Nd:YAG laser. A series of calculations were done to model the ablation process and various ablation parameters of the system, and the ion trajectories of the ablated ions were modeled with the computer program SIMION. Many studies were carried out under vacuum using an ion-drift system and mass analysis in a residual gas analyzer (RGA). The ablation target and laser optics were moved to the gas cell and several ablation studies were performed, including measurements of the extraction time and the ion mobility for ions traveling through the gas cell.