Numerical simulations and experiments of simultaneous acceleration of positive and negative ions in a radio frequency quadrupole

A continuous dc beam can be gradually bunched into a series of buckets in radio frequency quadrupole (RFQ) accelerators. For positive and negative ions, there are two buckets in every rf period, respectively. If both ions are mixed and simultaneously injected into the RFQ, they can be bunched into their own buckets 180 degrees apart in the same rf period. When positive and negative ions are homogeneously mixed, neutralization of space charge is automatically realized in the region between the bending magnet for beam mixing and the bunching section of the RFQ; then the emittance growth of the mixed beams is restrained, because the space charge fields are weakened by full or partial charge neutralization. However, as the continuous beam begins to be bunched and accelerated, the ions with a different sign of charge exert forces that resist the separation of the ions, so the transmission efficiency is not improved compared with single beam acceleration [1-3]. However, it is still attractive in some applications that the total output beam flux can be easily doubled by simultaneous acceleration of ions injected from a positive and a negative ion source. The integral split ring (ISR) RFQs have been developed at Peking University since the 1980s in collaboration with the Institute of Applied Physics (IAP) at Frankfurt University [4]; up to now two ISR RFQs have been commissioned [5,6]. To investigate the feasibilities and advantages of the simultaneous acceleration of positive and negative oxygen ions in an ISR RFQ, numerical simulations and dual beams acceleration experiments have been carried out.Physics, NuclearPhysics, Particles & FieldsSCI(E)0ARTICLE2null