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The article represents a review of direct extraction sources of negative hydrogen ions. During the past year or so interest in this method of producing high intensity beams of negative ions has increased considerably because of new developments resulting in currents of more than 20 mA. The first part of the article deals with inelastic collisions between particles which lead to the creation or destruction of negative ions. The knowledge of such elementary processes is relevant because the intensity of extracted H− currents is determined primarily by the equilibrium between the competing processes of creation and destruction. Attempts by several authors to analyze theoretically the production of H− ions in the plasma of a discharge will be explained subsequently and their results compared with experiments. Four types of direct extraction sources will be described next: duoplasmatrons, hollow discharge duoplasmatrons, Penning sources, and magnetron sources. Details of their design and beam characteristics will be given, as well as suggestions for further improvements.

, and greater than 55nC total extracted ion charge. The Test EBIS utilizes the full electron beam power but has only half the trap length and operates at a reduced duty factor compared with an EBIS for RHIC, which would produce at least 85nC total ion charge in 10-40 microsecond pulses, containing ~3x10 9 particles/pulse of Au 32+ ions. Normalized rms emittance values for 1-3mA extracted ion beams have been in the range of 0.08-0.1 pi mm mrad. Present development of the source is focused on establishing operational reliability and facilitating future upgrades in ion intensity and species, since the major emphasis is now on integrating the EBIS into a pre-injector facility, including an RFQ and linac. Recent progress towards this goal includes the following: 1) An IrCe electron gun cathode and modified anode have been installed in an electron gun chamber separable from the source ionization region by a gate valve. A very low loss 10A, electron beam has been propagated with the new configuration, with 100kW peak power dissipation at the electron collector. 2) A new electron collector power supply configuration has been tested which can lower the cost compared to our present setup, while improving the stability of the electron beam launch. This is an important first step towards placing the EBIS on a nominal 50kV platform, necessary for efficient highly charged ion transport to the RFQ. 3) A hollow cathode ion source obtained from CEA Saclay, [1] has been tested and is being installed. This will allow us to provide a variety of ion species to the RHIC and NASA Space Radiation Laboratory facilities, and is valuable at the present project stage for beamline development and emittance studies of heavy and light ion beams of highly charged ions from the EBIS. 4) An electron collector for RHIC has been designed which would allow operation exceeding 10A electron beams at 100% duty factor. The RHIC collector design could allow upgrades to 300kW electron beam power.[2] 5) Controls for pulse to pulse switching and diagnostics for charge state and charge fraction verification have been developed.

A retarding potential technique has been employed to select electrons for extraction from a hollow cathode discharge. In ‘‘normal’’ operating pressures, the electron distribution function is Gaussian like with a superthermal tail. At low operating pressures, the electron distribution function has an additional distinct component of electrons with a very low thermal spread of 0.13 eV and an energy corresponding to the cathode potential.

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