Design study of a multipole ion trap for beam physics applications

A unique linear Paul trap is designed for a systematic experimental study of nonlinear beam dynamics with the tabletop apparatus 'S-POD' at Hiroshima University. S-POD is the abbreviation of 'Simulator of Particle Orbit Dynamics' where we can produce a non-neutral plasma physically equivalent to a charged-particle beam in an alternating-gradient focusing channel. Unlike a regular Paul trap with four quadrupole rods, the present trap configuration includes extra electrodes that enable us to control the strengths and time structures of low-order nonlinear fields independently of the linear focusing potential. We here consider the insertion of thin metallic plates in between the quadrupole rods. The size and arrangement of those extra electrodes are optimized by using a Poisson solver. Simple scaling laws are derived to make a quick estimate of the sextupole and octupole field strengths as a function of the plate dimension. Particle tracking simulations are performed to demonstrate the controlled excitation of nonlinear resonances in the modified Paul trap. (author)