Space charge lenses for particle beams

Space charge lenses provide strong cylinder symmetric focusing for low-energy high-perveance particle beams using a stable space charge cloud. They need drastically reduced magnetic and electrostatic field strength compared with conventional systems and are superior for a degree of lens filling above 17%. They can theoretically provide linear transformation in phase space and reduce beam aberrations and space charge forces. The density distribution of the enclosed space charge is given by the transverse and longitudinal enclosures of the cloud. By the use of self-consistent simulations of the space charge cloud, the focusing properties of space charge lenses in the presented design can be forecasted with sufficient quality. The presented simulations show that the theoretical values can be reached locally. The results of our investigations on the beam transport in a high-current test injector equipped with space charge lenses, including emittance measurements, will be presented and discussed. They show that significant improvements of lens operation have been reached by the reduction of the residual gas pressure and a careful design of the external fields using numerical simulation techniques to calculate the local density distributions. Comparisons of the experimental results with the beam transport simulations show good agreement concerning both focusing strength and linearity of phase space transformation. For the lens design used, the observed degree of lens filling is at least 38% of the theoretical value and more than twice the threshold value. (c) 2005 American Institute of Physics.