Highly Charged Ions Generated in a Pinched Electron Beam

Usually in an electron beam ion source (EBIS) the electrons are radially confined by a strong magnetic field, resulting in a constant electron density. In a XEBIST (X = crossover, T = trap) without confining magnetic field the current density is determined by beam spreading due to the beam space charge and optimized by proper matching with a lens system. By continuous production of ions and the increase of their charge states the space charge neutralization of the electron beam increases until a stationary state is reached Therefore, the effective current density in the trap will increase. Caused by the magnetic self field of the electron beam a further compression can be observed. According to this relativistic pinching effect even higher current densities may be expected at electron energies of some 100 keV than with magnetic confining field. In order to demonstrate this behavior we have set up an XEBIST to operate up to 65 keV and observed in first experiments at 22 keV an increase of the average current density from 10 to 150 Acm^-2 at 40 ms neutralization time. Highly charged ions like Ar¹⁶⁺ could be produced in this way.