Ion beam transport and focusing experiments

The CASTOR accelerator has been fitted with an applied Br extractor diode for use in ion beam transport and focusing experiments. The beam, composed mainly of protons, is accelerated to 300–400 keV. Beam propagation in vacuum is observed to be consistent with divergences of 50 mrad HWHM in the radial direction and 125 mrad HWHM in the azimuthal direction and is observed to be constant through the beam pulse. Collective focusing of protons and electrons by a solenoidal lens is observed. The radial profile of the focus is as expected for the measured divergences. Improved focusing due to a two lens system that simultaneously compensates for radial divergence and beam energy spread [J. C. Olson and B. R. Kusse, J. Appi. Phys. 70(10)5719] has yet to be demonstrated. Long time scale conductivities of 0.5–1.0 × 10¹³ s⁻¹ are measured in beam ionized nitrogen plasmas.