Abstract
The crossover electron beam ion source (XEBIST) without confining magnetic field has made an important step towards higher electron beam energies. By proper matching using a magnetic lens system, a high compression of the electron beam has been achieved. The importance of reducing the lens aberrations by partial neutralization of the beam space charge in the lens section has been demonstrated. The effective current density in the trap region has been further increased by self-pinching in connection with space-charge neutralization. In our first experiments at an electron energy of 22 keV, the average current density in the trap increased from 10 to 150 A/cm2 at 40 ms neutralization time. Highly charged ions like Ar17+ were produced in this way. The combined Penning ion trap and electron beam source (PITEBIS) was operated successfully by radio-frequency modulating the current of the electron beam. This new kind of modulation could be used not only for cleaning EBIS sources from unwanted ion species but also to enhance the yield of highly charged ions by ion cooling. The effect of selective rf heating is demonstrated.
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