High-intensity Negative Ion Sources Research Articles

A review of diagnostic techniques for high-intensity negative ion sources

Plasma and beam diagnostic methods for high-current-density negative ion sources are reviewed. The pulse laser–induced photodetachment method was widely used to measure negative ion density in the ion source plasma. The method was used to understand fundamental processes of negative hydrogen (H−) ion formation and destruction in hydrogen plasmas. Species composition and plasma parameters in H− ion sources can be estimated from optical emission spectroscopy data, while electrostatic probes are utilized to obtain local plasma parameters in the ion source. Plasma transport toward the extractor is studied by combining a laser beam for photodetachment and a structured electrostatic probe to visualize a flow pattern of H− ions. Spatial distributions of large-area H− ion beams are monitored by infrared thermography images, showing interactions among multiple beamlets. These diagnostic methods deepen the understanding of how H− ions are produced and extracted through beam-forming apertures. The acquired knowledge on ion source plasma and beam transport improves the ion source design of the next-generation H− ion sources for fusion experiments and accelerators. The essence of research and development for negative ion source study is summarized through briefly tracing the history.

A compact multi-sample high-intensity negative ion source

A high-intensity cesium sputter negative ion source was designed for accelerator mass spectrometry. The source was developed and built in Triumf and is currently being used at the Rehovot pelletron tandem. The source features an internal cesium oven and simplified target insulation. A pneumatically actuated sample changer contains a 28-target wheel but allows manual loading of a single target as well. Negative ion beam currents obtained match or exceed those of ion sources of similar designs; the current remains constant for hours and low memory effects are observed as the targets are cycled.

The emittances and brightnesses of high-intensity negative ion sources

The emittances of high-intensity ion beams extracted from cesium sputter negative ion sources equipped with cylindrical and ellipsoidal solid tungsten and spiral-wound tantalum (General Ionex Corporation, Model 860) cesium surface ionizers have been measured for several ion species, including 12C −, 28Si −, 58Ni −, and 197Au −. While certain sets of data from the ellipsoidal and cylindrical geometry ionizer sources suggest a moderate growth in emittance with increasing negative ion beam intensity I over the range of intensities investigated (5 ⩽ I ⩽ 60 μA) of perhaps 20%, not all data exhibit this dependence, especially those from the Model 860 source. As well, no evidence of a monotonic dependence of emittance on ion mass was found. The emittances of ion beams at the 80% intensity levels from the Model 860 source are found to be higher on the average by factors of 1.8 and 1.7, respectively, than those from sources equipped with ellipsoidal and cylindrical geometry cesium surface ionizers. Brief descriptions of the emittance-measuring device and the sources investigated are given. Emittance and brightness data for dc operation of each of the sources considered are presented and comparisons made of the results.

Development of a high current negative ion source for fusion application.

Negative ion based neutral beam injector is one of the most attractive heating system in future fusion reactors. In realizing the system, the crucial device which has to be developed is a high intensity negative ion source. Significant progress has been made on the negative ion source in these years. Among them, a few ampere negative ion beam were produced stably, while the divergence of negative ion beams becomes to be as low as<10 mrad. We consider these results are demonstrating the potential of the negative ion source for the heating device in future reactors.

Emittance studies of high intensity negative ion sources equipped with continuous surface cylindrical and spherical geometry tungsten ionizers

A digitally controlled emittance measurement, data acquisition and processing system has been designed, implemented and used to determine emittances of negative ion beams extracted from high intensity negative ion sources equipped with cylindrical and spherical geometry cesium surface ionizers. Comparative studies indicate that the emittances of ion beams extracted from the source equipped with a spherical geometry ionizer are lower by 13–21% than those extracted from the source equipped with a cylindrical geometry ionizer. This difference may be attributable to geometric factors rather than differences in the sizes of the emission areas at the points of negative ion generation. Studies reveal that the emittances of these sources are independent of ion mass for most of the materials investigated and independent of ion current over the range of ion currents used in these investigations (4–12 μA).

Possible use of synchrotrons as post-acceleration boosters for tandems

The recent development of a high intensity negative ion source and the demonstration that intense heavy ion beam bursts can be accelerated by a large tandem make synchrotrons a possibly attractive alternative when considering different types of tandem injected heavy ion booster accelerators.

Studies associated with the development of a modified university of Aarhus negative ion source

A high intensity negative ion source, based in principle on a source developed at the University of Aarhus, has been designed and constructed. This source demonstrates a high degree of reliability, operational stability and long lifetime. The plasma generation mechanism produces a uniform plasma density and thus uniform sputter probe wear. The results of studies associated with the source development are given which establish relationships between negative ion yield and certain operation parameters - principally oven temperature and sputter probe voltage. The parameters for maximizing yields from a number of elemental materials were observed to occur at oven temperatures of ∼ 200°C and sputter probe voltages between −900 and −1200 V depending upon the cathode material. Negative ion yields are observed to increase with sputter probe voltage according to a theoretically predictable V 5 2 law. The important design aspects of the source and negative ion yields observed to-date are given. Application of the Langmuir-Saha theory is made to the yield data and changes in work function necessary to produce observed negative ion yields are computed. The measured changes in work function agree in several instances with the theoretical formulation of Broeder et al. 22).

635. Design considerations for high intensity negative ion sources: K W Ehlers, Nuclear Instrum Methods, 32 ( 2), Feb 1965, 309–316

635. Design considerations for high intensity negative ion sources: K W Ehlers, Nuclear Instrum Methods, 32 ( 2), Feb 1965, 309–316

Design considerations for high-intensity negative ion sources

An attempt has been made to improve the output of negative hydrogen ions, which are extracted directly from a hot-cathode Philips-ion-gauge type of discharge. The discharge chamber has been modified to accord with assumptions made as to the probable formation mechanism of the negative ions observed. Negative hydrogen ion currents in excess of 5 mA have been obtained. Ion source operating parameters, as well as considerations for the utilization of this discharge geometry by negative ion cyclotrons, are discussed.

Design Considerations for High-Intensity Negative Ion Sources

The production of negative hydrogen ions (H-) by an ion source similar to that employed in many cyclotrons has been studied. The negative ions are extracted directly from the arc plasma in a direction normal to the magnetic field without use of a charge-exchange medium. In an attempt to improve the negative-ion yield, the arc-discharge chamber has been modified to conform to assumptions made as to the probable formation mechanism of the observed negative ions. Outputs of negative hydrogen ions in ex cess of 5 mA have been obtained. Ion-source operating parameters are discussed, as well as considerations for the utilization of this discharge geometry by negative-ion cyclotrons.

High-intensity negative ion sources

The production of beams of negative deuterium ions has been studied with two ion sources with geometries that could be employed in a cyclotron. The negative ions were extracted directly from the arc in a direction normal to the magnetic field without using a charge-exchange medium. With a high gas pressure in the arc and an current of 5 A, a 2-mA beam of D − ions was obtained.