Beam-energy distribution measurements of liquid gallium field-ion sources

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Abstract
Measurements are reported on the energy distribution of the ion beam produced by Ga liquid metal ion sources, for a range of emission currents, i approximately 1-50 mu A. The full width at half-maximum (FWHM). Delta E1/2, of the energy distribution curves varies from approximately 4.5-5 eV at approximately 1 mu A to approximately 35 eV at 50 mu A. Three regions can be detected in the Delta E1/2 versus i curve. In the first region, between approximately 0.6 and 2 mu A, Delta E1/2 varies very slowly with current. In the second region, above approximately 2 mu A and extending up to approximately 25 mu A, the curve rises steeply with current, in fairly good agreement with the predicted Delta E1/2 varies as i2/3 relation. For i>or approximately=25 mu A the curve deviates markedly from this relation, and tends to flatten. Although a tentative explanation for the deviation from theory at high currents may be given in terms of gross instabilities of the anode, the deviation at very low currents (where Delta E1/2 is almost constant with i) is not understood.

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