Space Charge Dominated Ion Beams Research Articles

Feasibility study of the magnetic beam self-focusing phenomenon in a stack of conducting foils: Application to TNSA proton beams

AbstractThis paper investigates prospects of utilizing a high-power laser-driven target-normal-sheath-acceleration proton beam for the experimental demonstration of the magnetic self-focusing phenomenon in charged particle beams. In the proposed concept, focusing is achieved by propagating a space-charge dominated ion beam through a stack of thin conducting and grounded foils separated by vacuum gaps. As the beam travels through the system, image charges build up at the foils and generate electric field that counteracts the beam's electrostatic self-field — a dominant force responsible for expansion of a high current beam. Once the electrostatic self-field is “neutralized” by the image charges, the beam currents magnetic self-field will do the focusing. The focal spot size and focal length depends on the choice of a number of foils and distance between foils. Considering the typical electrical current level of a target-normal-sheath-acceleration proton beam, we conclude that it is feasible to focus or collimate a beam within tens of millimeters distance, e.g., using 200–1000 Al foils, 0.5 µm thick each, with foil spacing ranging from 25 µm to 100 µm. These requirements are within technical capabilities of modern target fabrication, thus allowing the first possible demonstration of the pinch effect with heavy ion beams.

A new non-invasive approach for the measurement of ion beam energy

A non-invasive approach for the measurement of the kinetic energy of space-charge dominated ion beams is proposed based on measurements of beam current signals at two different positions. We found that the evolution of space-charge waves, which are generated by weak voltage variations in induction accelerator gaps, can be computed precisely by Fourier analysis of the current signals. The beam energy profile can then be derived from the current signals including the effect of transient space-charge waves. Through analytic studies of the space-charge wave propagation, confirmed by 3-D PIC simulations, we show that the current signals are remarkably sensitive to the weak voltage variations.

Ion optics of RHIC electron beam ion source

RHIC electron beam ion source has been commissioned to operate as a versatile ion source on RHIC injection facility supplying ion species from He to Au for Booster. Except for light gaseous elements RHIC EBIS employs ion injection from several external primary ion sources. With electrostatic optics fast switching from one ion species to another can be done on a pulse to pulse mode. The design of an ion optical structure and the results of simulations for different ion species are presented. In the choice of optical elements special attention was paid to spherical aberrations for high-current space charge dominated ion beams. The combination of a gridded lens and a magnet lens in LEBT provides flexibility of optical control for a wide range of ion species to satisfy acceptance parameters of RFQ. The results of ion transmission measurements are presented.

Matching and transporting an intense ion beam through a solenoid focusing channel

An experiment to inject and match a $10\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, singly charged ${\mathrm{K}}^{+}$ ion bunch at an ion energy of 0.3 MeV, current of 45 mA, and dimensionless perveance of ${10}^{\ensuremath{-}3}$ 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.

Simulation and Observation of the Long-Time Evolution of the Longitudinal Instability in a Cooler Storage Ring

In the ESR heavy-ion cooler storage ring at GSI the exponential growth and the subsequent saturation phase of the longitudinal instability in space charge dominated ion beams can be monitored with high resolution. Kinetic simulations together with the experimental data lead to a new insight into the effects of space charge and electron cooling on the long-time evolution of the instability. In the simulations we observe the continuous excitation of long-lived collective modes generated by particle trapping in the self-excited potential, which suggest that previous ``overshoot'' concepts need revision.

New design method for the extraction electrodes of high-brightness space charge dominated ion beams

A nonideal potential distribution inside an ion gun gives rise to emittance growth of the beam. The aberrations caused by the lens system (extractor) and the space charge of the beam can be reduced to a minimum by appropriately modifying the shape of the anode. For an intense Cs+ beam this was reached in a computer experiment and realized with the aid of numerically controlled machines. Experimentally the brightness of the beam could be shown to exceed the value at the conventional design by a factor of about 3.

Envelope instability in low-energy proton synchrotrons

In this paper we investigate the limits on beam intensity in low-energy proton synchrotrons due to the instability of the beam envelope. This instability has been previously examined in the context of space charge dominated ion beams, in particular for inertial confinement fusion applications. We generalize the formalism of beam envelope evolution to include effects found in circular accelerators, i.e. curvature focusing and momentum dispersion. Several example lattices are analyzed to determine intensity limits imposed by onset of envelope instability; it is found that the instability can occur without depressing the phase advance below 90° per cell.