High Reliability, Long Lifetime H- Ion Source

In this work, a long lifetime (greater than 6 months) H- ion source capable of reliably delivering current greater than 10 mA will be designed. The immediate DoE need for this technology is a reliable DC H- ion source that will inject an ion beam into the proposed Project X particle accelerator at Fermi National Laboratory. There are several other basic science, medical, energy, and industrial applications for which this technology will enhance capabilities if the technical approach proves successful. Existing H- ion sources embed the H- production in a plasma environment. Inevitability, these H- production processes lead to transport and extraction complications. Disadvantages of existing H- sources relative to H+ sources are power and gas inefficiencies, leading to pulsed (low duty factor) operation and large vacuum facilities to maintain injector pressure. Larger duty factor and continuous wave H- sources have comparatively short lifetimes before ion source refurbishment is required. A mechanism to produce hyperthermal hydrogen atoms (2-5 eV) via the interaction of molecular hydrogen ions with electrons generated in a 2.45 GHz microwave source (MWS) will be developed. These atoms will then be converted to H- ions via surface and volume conversion mechanisms. Recent advances in positive ion sources using the resonant interaction of 2.45 GHz microwaves in hydrogen gas in the presence of an 875 Gauss magnetic field have led to intense DC positive ion beams. Twenty five percent efficiency in converting hydrogen gas into positive ions using 1 kW of microwave power has been routinely observed. MWSs are becoming increasingly common in commercial use due their inherent DC operating capability. Theoretical studies imply that positive ion sources can be modified to be good sources of atomic hydrogen and negative ion beams. Though H- ion sources enjoy several advantages over positive ion sources, their commercial use has been limited by their short lifetime. In this work, a modified 2.45 GHz microwave proton source will be used as a source of hydrogen atom beams that will be surface converted to H- ions. The anticipated result will be an extremely reliable DC H- ion source capable of producing high beam currents (greater than 10 mA), which will enable a wide range of government and commercial applications including isotope production and separation, silicon cleaving for semiconductor applications, cyclotron injectors, and ion injectors for magnetic confinement fusion energy.