Abstract
Linear and nonlinear resonant instabilities of charged-particle beams traveling in periodic quadrupole focusing channels are studied experimentally with a compact non-neutral plasma trap. The present experiments are based on the idea that the collective motion of a beam in an accelerator is physically similar to that of a one-component plasma in a trap. A linear Paul trap system named ``S-POD'' (simulator for particle orbit dynamics) was developed to explore a variety of space-charge-induced phenomena. To emulate lattice-dependent effects, periodic perturbations are applied to quadrupole electrodes, which gives rise to additional resonance stop bands that shift depending on the plasma density. It is confirmed that an $m$th-order resonance takes place when the corresponding tune of an $m$th-order collective mode ${\ensuremath{\Omega}}_{m}$ is close to a half integer.
Highlights
The quality of a charged-particle beam can be seriously deteriorated by collective instabilities originating from space-charge self-fields [1,2,3]
Since data obtained are analogous for other values of Nsp, we only describe results on Nsp 1⁄4 12
A systematic study of coherent betatron resonances was performed with the new experimental tool ‘‘S-POD’’ that approximately reproduces the center-of-mass frame dynamic motion of a charged-particle beam evolving in a periodic focusing lattice
Summary
The quality of a charged-particle beam can be seriously deteriorated by collective instabilities originating from space-charge self-fields [1,2,3]. Paul ion traps have been widely utilized for diverse purposes associated with frequency standards, Coulomb crystals, quantum computing, high-accuracy spectroscopy, and others [12,13,14,15,16,17], we designed and constructed S-POD solely for experimental beam physics. We report on recent S-POD experiments performed to identify the parameter regions in which an intense hadron beam becomes unstable in a periodic quadrupole lattice due to collective resonances. Mechanical errors of the trap somewhat enhance nonlinear resonances, such instability can occur in an intense beam even if the driving force is perfectly linear [23,24].
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