Single-ring magnetic cusp ion source

Journal Article · Tue Nov 01 00:00:00 EST 1983 · Rev. Sci. Instrum.; (United States)

DOI:https://doi.org/10.1063/1.1137275· OSTI ID:5667497

Brainard, J P; O'Hagan, J B

The single-ring cusp ion source discussed in this paper was developed to provide a dc ion beam in a nonpumped D--T neutron generator. The source operates at 0.25 Pa and produces a uniform-density beam through an aperture of 1.3-cm diameter. At the standard operating voltage of 150 V and arc current of 10 A, the atomic ion content of the 200-mA deuterium ion beam is about 60%, and the ion impurity level is less than 0.5%. The ion output of the source was examined at arc currents of up to 40 A and found to be a linear function; in addition, very high D/sup +/ yields were realized. With the aid of a shielded Langmuir probe, we have determined such plasma properties as electron energy, plasma potential, floating potential, and current density throughout the volume of the source. It was observed that the plasma is effectively confined by the magnetic field and there is evidence of an electron energy filtering mechanism similar to that found in multicusp ion sources. Electron energy on the filament side of the cusp has been determined to be about 75 eV and on the aperture side about 12 eV. Since the electron impact cross section for ionizing diatomic deuterium is maximum at 75 eV and the cross section for dissociating D/sup +//sub 2/ to D/sup +/ is greatest near 12 eV, we believe that a very effective two-step ionization process accounts for the high D/sup +/ yield of the single-ring magnetic cusp source. Plasma potentials measured have values close to the voltage of the anode, and the floating potentials are seen to be directly related to electron energy values. The floating potential is near cathode voltage where electron energies are high, and close to anode voltage where electron energies are low.

• Research Organization: Sandia National Laboratories, Albuquerque, New Mexico 87185
• OSTI ID: 5667497
• Journal Information: Rev. Sci. Instrum.; (United States), Vol. 54:11
• Country of Publication: United States
• Language: English

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