Abstract
Longitudinal bunching factors in excess of 70 of a 300-keV, 27-mA ${\mathrm{K}}^{+}$ ion beam have been demonstrated in the neutralized drift compression experiment [P. K. Roy et al., Phys. Rev. Lett. 95, 234801 (2005)] in rough agreement with particle-in-cell source-to-target simulations. A key aspect of these experiments is that a preformed plasma provides charge neutralization of the ion beam in the last one meter drift region where the beam perveance becomes large. The simulations utilize the measured ion source temperature, diode voltage, and induction-bunching-module voltage waveforms in order to determine the initial beam longitudinal phase space which is critical to accurate modeling of the longitudinal compression. To enable simultaneous longitudinal and transverse compression, numerical simulations were used in the design of the solenoidal focusing system that compensated for the impact of the applied velocity tilt on the transverse phase space of the beam. Complete source-to-target simulations, that include detailed modeling of the diode, magnetic transport, induction bunching module, and plasma neutralized transport, were critical to understanding the interplay between the various accelerator components in the experiment. Here, we compare simulation results with the experiment and discuss the contributions to longitudinal and transverse emittance that limit the final compression.
Highlights
Heavy ion fusion (HIF) and ion-driven warm dense matter (WDM) physics applications require short duration, high power ion pulses delivered to small radius targets [1
A simulation with the more realistic 3-eV initial plasma temperature and Tk 0:02 eV resulted in an increase in the beam emittance of 25%. This increase in k will have an impact on compression in the neutralized drift compression experiment (NDCX) experiment possibly reducing CR up to 25%
Given an ion source temperature of 0.1 eV at the anode, longitudinal cooling of the beam as it accelerates in the diode produces Tk < 0:01 eV
Summary
Heavy ion fusion (HIF) and ion-driven warm dense matter (WDM) physics applications require short duration, high power ion pulses delivered to small radius targets [1–. Neutralized drift compression (NDC) of these intense space-charge-dominated ion beams makes use of a temporal velocity tilt and neutralizing background plasma to achieve short pulse lengths and small radial spot. In both HIF and WDM scenarios, transverse and longitudinal focusing forces are applied to the individual ion beams outside of the target chamber. Avoiding the usual problems of numerical heating on the computational grid With these algorithms we can efficiently explore the tightly coupled physics of ion acceleration, compression, and focusing of both recent and planned experiments on the NDCX. In the Appendix, a procedure for determining the optimum tilt waveform for axial compression is discussed
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