Sputter Type Negative Ion Source Research Articles

Measurement of negative-ion-production efficiencies and development of a dc operation sputter-type negative ion source

For the development of a high current heavy negative ion source, the production efficiency of the negative ions by Xe+ sputtering with cesium and electron detachment cross sections in xenon gas were measured. The maximum efficiency for Cu− was 12.1% and the single-electron detachment cross section was found to be of the order of 0.6–1.4 × 10−15 cm2 in the energy range of 5–50 keV. Based on the results of these fundamental experiments, a plasma-sputter-type heavy negative ion source has been constructed, in which the plasma was generated at a rf-frequency of 13.56 MHz. A total negative ion current of 2.5 mA was obtained without electrons from the source in dc operation, and the Cu− current was detected to be 91% of the total beam. The operation characteristics are described.

The thermophysical characteristics of the ionizer in cesium sputter-type negative ion sources

The thermophysical characteristics of the ionizer in cesium sputter-type negative ion sources is studied by means of the heat transfer theory in this paper. A heat transfer model is given and theoretical calculations are performed. The theoretical calculations are in good agreement with experimental results. Based on the theoretical analysis the configuration of the source is improved and the calorific efficiency is increased, so that the temperature of the ionizer can reach up to 1300 K and the lifetime of the heater core of the ionizer is prolonged. The theoretical model can serve as the basis for the ionizer design of the cesium sputter-type negative ion sources. In addition, the study is also helpful for the design of the heater in the similar ion sources.

Emittance calculations and measurements for a sputter-type negative-ion source

A method for calculating the beam current and emittance of a negative-ion beam from a sputter-type source is described. In this ion source a Cs + beam of up to several mA originates by surface ionization on a hot, high-work-function surface. Cs + ions with an energy of a few keV strike the Cs-coated cathode where they produce by sputtering negative ions of the cathode material. The calculation involves tracing trajectories of the Cs + ions that bombard the cathode surface and also trajectories of the sputtered negative ions. The dependence of the beam current, emittance and average brightness on several ion source parameters is discussed. These parameters include the cathode voltage and details of the ion source geometry such as cathode shape and exit-aperture diameter. Results of the calculations are in good agreement with measurements of emittance for cases in which space charge effects are negligible. For negative-ion currents greater than a few tens of μA and for Cs + currents greater than 1–2 mA the measured emittance generally exceeds the calculated emittance if space charge is neglected in the calculation. The calculations have suggested several improvements in the design of the source that were later implemented experimentally to optimize utilization of the Cs + beam and to increase the negative-ion extraction efficiency. The ion source lifetime, beam energy spread and the effects of cathode erosion are also discussed.

Calculated and Measured Emittance of a Sputter-Type Negative-Ion Source

A method for calculating the beam current and emittance of a negative ion beam from a sputter-type source is described. Calculations are compared to measured emittance. The dependence of the emittance on ion source parameters such as cathode shape, exit aperture diameter, and cathode voltage is discussed.