Emittance measurements of gallium liquid metal ion sources

The emittances of momentum-analyzed 69Ga+ ion beams extracted from a needle-type liquid-metal ion source (LMIS) are found to be approximately twice as large in the dispersive plane (x-direction) as in the orthogonal, nondispersive plane (y-direction). This effect is principally attributable to dispersion of the beam in the x-direction by the mass analyzing magnet used in the experiments. This dispersion results from space charge effects and other sources of intrinsic energy spread within the ion beams. In addition, the growth of emittance with beam intensity is less dramatic in the y direction, also suggesting the effect of energy dispersion. It is argued that y-direction emittance values should be considered as representative of the gallium LMIS whenever energy dispersive devices are not incorporated in the beam transport system. Brief descriptions of the experimental hardware are given and x- and y-direction emittance data are presented in this report. 37 refs., 3 figs