Influence of extraction grid on ion beam characteristics

This work is a part of the development of a laser ion source (LIS) for multiply charged ion injectors. This experiment is devoted to the investigation of the effect of a metal grid on the extracted ion characteristics. The energy spectra of the ions in the plasma expanding into a drift tube with and without a grid have been compared. Plasmas of two different target materials, carbon and tungsten, were generated by the CO₂ laser pulses with the focal power density on the target of about 10¹¹ W/cm². The time-of-flight method with an electrostatic energy analyzer installed just behind the grid is used to measure the charge states and energy distributions of ions. A significant effect of the grid on the ion energy distributions has been observed. This effect depends strongly on the ion mass and should be taken into account when designing a LIS, especially in the case of heavy ions.