Thirty years of surface plasma sources for efficient negative ion production

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  • Vadim Dudnikov
    Fermi National Accelerator Laboratory, Batavia, Illinois 60510

Abstract

<jats:p>Thirty years ago, July 1, 1971, significant enhancement of negative ion emission from a gas discharge following a small admixture of cesium was observed for the first time. This observation became the basis for the development of the Surface Plasma Source (SPS) for efficient production of negative ions. In the SPS, negative ions are produced from the interaction of plasma particles with electrodes on which adsorbed cesium reduces the surface work function. Following this discovery, the emission current density of negative ions increased rapidly from j∼0.01 A/cm2 to 3.7 A/cm2 with a flat cathode and up to 8 A/cm2 with optimized geometrical focusing in a long pulse SPS and up to 1 A/cm2 for a dc SPS. Charge-exchange cooling decreases a negative ion temperature below 1 eV and increases the negative ion brightness by many orders to a level compatible with the best proton sources, B=j/T&gt;1 A/cm2 eV. The intensity of negative ion beams was increased from mA to tens of amperes. Features of different SPS’s, negative ion beam formation, transportation, space-charge neutralization over neutralization and instability damping are considered. Practical aspects of SPS operation and high brightness beam production will be discussed.</jats:p>

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