ELECTROSTATIC OCTUPOLE LENS CALCULATIONS FOR MEV ION ACCELERATORS

In the application of a tandem electrostatic accelerator (NEC Pelletron) to accelerator mass spectrometry for stable isotopes, various optical elements are needed. These optical components are electrostatic dipoles, quadrupoles and octupoles. Cylindrical configurations of rods of circular cross section have been shown [J. Kelly, Adv. Electron. Electron Phys. 43 (1977) 43] to provide many of these desired features. In the present work, we present new designs using cylinders in a cylindrical arrangement which provide, when appropriately excited, dipoles, quadrupoles and octupoles. These configurations can be excited so as to produce combinations of these multipoles as well, thus permitting correction for aberrations. The results of optimization of the geometry using various eight electrode arrangements are reported and compared to previous four electrode and other geometries.