Further aspects of enhanced ion scattering near 180 degrees.
The role of rainbow scattering in enhanced ion scattering near 180{degree} was explored by comparing calculated enhancements for protons and antiprotons. Since the rainbow effect does not occur for negative particles and since the enhancement was much smaller for them than for positive particles, this comparison demonstrated in a more direct way than previously done the importance of rainbow scattering in producing the enhancement. A procedure for calculating a similarity factor between the ingoing and outgoing portions of a trajectory was developed, and its use showed that trajectories returning near 180{degree} differ in nature from random-return trajectories. A discussion is given of the possible relationship of the enhancement to phenomena such as the correlation effect in self-diffusion by the vacancy mechanism in solids and surface-structure studies by impact-collision ion-scattering spectrometry.
Role of reversibility in enhanced ion backscattering near 180° scattering angle
Computer simulations show that recently measured enhanced ion scattering near 180\ifmmode^\circ\else\textdegree\fi{} originates in the reversibility property of ion trajectories. The simulation results explain the observed angular and depth dependence of the effect and predict a slight deficit in scattering at angles beyond the enhancement region that was not found experimentally. Collision-induced recoils of the target atoms and the depth resolution of the detector each produce sizable reductions in the effect, and their inclusion in the calculations in necessary for satisfactory agreement with experiment. The observed dependence on atomic number of the target is shown to be partly due to the nuclear charge and partly due to the dependence of target-atom recoils on mass. A calculation is also given of an enhancement to be expected under channeling conditions.
Magnetic plasma confinement for laser ion source.
A laser ion source (LIS) can easily provide a high current beam. However, it has been difficult to obtain a longer beam pulse while keeping a high current. On occasion, longer beam pulses are required by certain applications. For example, more than 10 micros of beam pulse is required for injecting highly charged beams to a large sized synchrotron. To extend beam pulse width, a solenoid field was applied at the drift space of the LIS at Brookhaven National Laboratory. The solenoid field suppressed the diverging angle of the expanding plasma and the beam pulse was widened. Also, it was observed that the plasma state was conserved after passing through a few hundred gauss of the 480 mm length solenoid field.