Search Results (5 total)

Longitudinal bunching factors in excess of 70 of a 300-keV, 27-mA K⁺ ion beam have been demonstrated in the neutralized drift compression experiment [P. K. Roy , 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.

Electron cloud and gas measurements were conducted in a solenoid lattice with a 10  μs, singly charged K⁺ ion bunch at an ion energy of 0.3 MeV and currents of 26 and 45 mA. The principal objective of these experiments is to control electrons and understand their impact on the beam dynamics. Electron clearing measurements indicate an electron density close to 1% of the beam density in the solenoid lattice is enough to partially neutralize the beam and cause the emittance to grow ≥40%. A new method of measuring the dynamics of beam-induced gas desorption, ionization, and electron emission for normal incidence is also presented. Stainless steel and copper targets exposed to a beam intensity of 1.6×10¹²  ions/pulse show ionized gas and electron densities approach the beam density in a single pulse. These measurements also show the gas cloud expands as a function of time and the dynamics are dependent upon the incident material and the bias voltage.

An experiment to inject and match a 10  μs, singly charged K⁺ ion bunch at an ion energy of 0.3 MeV, current of 45 mA, and dimensionless perveance of 10^-3 into a solenoid lattice has been carried out at LBNL. The principal objective of this experiment is to match and transport the space-charge dominated ion beam and compare predicted and measured emittance. Initial investigation also presented the opportunity to study electron cloud effects and the effects of misalignments. A qualitative comparison of experimental and calculated results are presented, which include time resolved current density, transverse distributions, and phase space of the beam at different diagnostic planes.

In a first beam dynamics validation experiment for a new Pulse Line Ion Acceleration (PLIA) concept, the predicted energy amplification and beam bunching were experimentally observed. Beam energy modulation of -80 to +150  keV was measured using a PLIA input voltage waveform of -21 to +12  kV. Ion pulses accelerated by 150 keV, and bunching by a factor of 4 were simultaneously achieved. The measured longitudinal phase space and current waveform of the accelerated beam are in good agreement with 3D particle-in-cell simulations.

Heavy ion drivers for heavy ion fusion and high energy density physics applications use space-charge-dominated ion beams which must undergo longitudinal bunch compression in order to meet the requisite beam intensities desired at the target. The Neutralized Drift Compression Experiment-1A (NDCX-1A) at Lawrence Berkeley National Laboratory is used to determine the effective limits of neutralized drift compression, which occurs due to an imposed longitudinal velocity tilt on the drifting beam and subsequent neutralization of the beam’s space charge with background plasma. The accurate and temporally resolved measurement of the ion beam’s current and pulse length, which has been longitudinally compressed to a few nanoseconds duration at its focal plane, is a critical diagnostic. This paper describes the design and experimental results for a fast and accurate ion beam probe, which reliably measures the absolute beam current in the presence of high density plasma at the focal plane as a function of time. A particle-in-cell code has been used to model the propagation of the intense ion beam and to design the diagnostic probe.