Physics and control of the afterglow HCI-beam pulsewidths for synchrotron and atomic physics

The afterglow operation modes in the ECR ion source (ECRIS) has found its applications not only in synchrotron accelerators but also in atomic physics, for it can provide a pulsed beam of highly charged ions (HCI) with much higher current than extractable at cw mode. However, control of pulsewidths and optimization of operation conditions are not a trivial matter without knowing the relevant physics. This paper explains several important physics discovered through analysis of ours and others experimental data. Experimentally observable typical ion-pulse waveforms, n/sub i/(t), were successfully simulated, including the timings of hot-electron loss. The time-dependent depth of the ion trapping potential-well, A(t), is only the information needed for the simulation of n/sub i/(t) at nonlinear mode. On the other hand, the electron density (n/sub e/), electron temperature, and charge state (Z) are needed for that of quiescent decay mode. Most importantly, this work has generated the evidences of the interchange instability (ICI), responsible particles for A(t), the presence of a hot-electron shell/ring, rotation of hot electrons, cold-electrons to stabilize ICI, and mass (M) to the Z dependence of the ICI-threshold. ICI theory predicts that a sharp-rising pulse is likely to be produced when M/Z is smaller, because the unstable equilibrium condition (n/sub h//spl ges/n/sub c/) is easily met before turning off the rf-power. The trailing edge of the pulse can be shortened by increasing the Z and n/sub e/, but decreasing the rf-power.