Neutral gas filled transport cells for high current electron beams

Applications of high current energetic electron beams often require reliable ways to transport and center them for injection into accelerator or beam steering systems. Magnetic transport has been successfully used in the past, but these systems require a coil system for high magnetic fields. Passive transport systems can be a much simpler way to accomplish the same result. The authors are conducting a series of experiments with a passive electron beam transport and centering system consisting of a conducting tube filled with neutral gas. The object is to study the transport and centering properties of the cell as a function of input beam current, transport cell length, cell diameter, fill pressure, and fill gas type. The electron beam is generated by NRL's Super IBEX accelerator which produces a 5.0-MeV, 50-kA, 40-nsec FWHM electron beam. The electron beam diode consists of a 6-mm diameter cold cathode and a 5-mil thick Titanium foil anode. The injected beams are < 2.0 cm diameter and have low divergence (<50 mrad). The experiments cover a wide range of parameters. The beam current is varied from 10--40 kA, the pressure from 0 to 100 mTorr, the transport length from 40--120 cm, the cell diameter from 5--10 cm and several gases (Ar,He) are used to examine the effects of ionization potential. The results of the experiments will be compared to computer simulations of SuperIBEX beams in the gas filled transport cells