[en] Some properties of emittance, emittance distributions, and measurement techniques are reviewed. In comparing the results of measurements with several different types of H^- sources with each other and with emittance formulae, it is concluded that the emittance of surface-type sources is dominated by the effective ion temperature. Other effects, such as ion-optical distortions, may account for the emittance of volume-type sources

[en] Time variation of space-charge forces in a beam-transport channel will lead to a time-averaged emittance growth of the beam. The Kapchinskii-Vladimirskii (K-V) equations have been used to follow the envelope of a round beam with effective beam current fluctuation i through a transport channel. The area of the ellipse that encloses the varying ellipses at the end has been used as the criterion for emittance growth. Simple formulae give the relation between i, initial emittance epilson, allowable fractional emittance growth Δ eta, effective average current I, average beam radius R, and transport length. For example, for a long transport channel a nominally compensated beam must have i < (βγ epsilon²I₀/R²)Δ eta, where I₀ = 4πepsilon₀Mc³/e, and βγ is the usual relativistic factor. Results for other conditions are presented. A comparison with a numerical calculation from the TRACE code for transport of a 100-keV, 100-mA beam is made. 6 refs., 3 figs

[en] The ratio of electrons to negative ions extracted from Penning surface-plasma sources (SPS) such as the 8X source is low even before any steps are taken to suppress the electrons. For the 8X source the e^-/H^- ratio is typically four or five to one for H^- operation and nine to one for D^- operation. Because the coextracted e^- present a power-loading problem to the 8X source extraction system, methods to dissipate and/or reduce the power in the e^- beam must be developed before extracting a dc H^- or D^- beam. Thus, an experiment was run to see if a collar installed in the near extraction region of the 8X source suppresses the electrons extracted from that source

[en] Up to 160 mA of H^- ions has been extracted at 20 kV from a 10 by 0.5-mm² slit in a Penning surface-plasma source. Typically, 70% of the beam can be transported through a bending magnet to a Faraday cup or emittance scanner. Up to 90% transmission has been observed for some neutralizing gases. Average and pulsed cesium flows from the source were measured with a surface-ionization gauge. Operating parameters of the source and measurements of the emittance are reported

[en] This paper describes three analytic approaches used to model electrostatic accelerator columns in beam-transport codes for low-current beams and compares the results of each approach with the results obtained by numerically calculating the electric field based on charge distribution on equipotential surfaces. The three analytic approaches described are (1) a cubic energy-gain approximation, (2) a cubic longitudinal electric-field approximation, and (3) the aperture equation. The first two approaches calculate impulse approximations at the apertures, whereas the third is an integration of particle trajectories through the column filed. The conditions under which the solutions tend to break down are discussed. 4 refs., 8 figs

[en] Ion-beam extraction systems may be optimized by ray-tracing codes. As a general criterion for comparing the geometry-dependent phase-space distributions, we first calculate the minimum-area ellipse that encloses all particles of any given two-dimensional phase-space distribution. Then, the relation between ellipse area and contained beam fraction is established by systematically finding and eliminating those particles that contribute most heavily to the emittance. Prescriptions for finding the minimum ellipse and beam fractions will be presented. The minimum and rms ellipses are compared for two code-calculated distributions that represent ion-beam extraction geometries. 5 refs., 6 figs

[en] The Los Alamos versions of the Penning Surface-Plasma Source (SPS) routinely generate H^- ion beams with pulsed currents over 100 mA. However, these sources employ geometries that result in the extraction of slit beams (0.5 x 10 mm²). Our modeling with the SNOW code indicates that the beam from a 5.4-mm-diam circular emitter will have lower emittance and divergence for transport to and injection into our radio-frequency quadrupole (RFQ) accelerator. This paper describes a newly constructed Penning SPS that has most of its discharge chamber dimensions scaled up by a factor of 4 to accommodate this circular emitter

[en] The possibility of using a Penning surface-plasma source (SPS) with rotating electrodes to produce dc H^- beams is investigated. In this rotating ion source (RIS), the average power density on the electrodes is reduced by magnetically confining the discharge to a small region near the emission slit while maintaining the geometry and instantaneous power density of the fixed-electrode Penning SPS. H^- beam currents (2.5 mA at 100% duty factor, 104 mA at 1.5% duty factor) and two-dimensional normalized emittances (0.036 π cm.mrad x 0.009 π cm.mrad for 40% of a 1.5-mA, dc H^- beam) similar to those of the fixed-electrode Penning SPS are produced by the uncooled RIS reported in this paper. The scaling to a 100% duty factor, fully cooled RIS is briefly discussed

[en] Circular emission-extractor electrodes are used to extract H^- ions from a Penning surface-plasma source, with the calculated space-charge limited current being observed. Emittance measurements are extended to include emittance as a function of beam fraction. Comparatively noise-free discharge voltages lead to factor of three reduction in emittance. Equal emittances in the transverse phase spaces are observed for the circular geometries

[en] An emissive probe has been developed to study the beam-plasma potential generated by a 20-keV, 30-mA/cm² quiescent H^- beam propagating in Xe background gas. An axial ion trap has been built, and its influence on the measured potentials is reported. The peak plasma potential at 10¹² cm^-3 Xe density increased from +5V to +10V when the ion-trap voltage was increased from zero to +80V. The quiescent H^- beam rms emittance, measured 34 cm from the ion source, increased from 0.012 to 0.023 π x cm x mrad when the Xe density was decreased from 2.2 x 10¹² cm^-3 to zero. 8 refs., 3 figs