Volume 71, Issue 2, February 2000
Index of content:
- NEGATIVE ION SOURCES FOR ACCELERATORS AND FUSION (I)
71(2000); http://dx.doi.org/10.1063/1.1150387View Description Hide Description
The multi-cusp ion source has been operated with 2 and 13.5 MHz in either pulse or cw mode for positive or negative ion beam production. Application of this type of source includes spallation neutron source,ion implantation,ion beam lithography, focused ion beam systems, radioactive ion beam production, and neutron generators. In order to achieve long life and reliable operation, different antenna arrangements have been explored. It is found that several antenna configurations can provide over 100 h of rf induction discharge operations.
71(2000); http://dx.doi.org/10.1063/1.1150388View Description Hide Description
Due to the development of reliable ion sources,charge-exchange injection into circular accelerators has become routine. For preacceleration of heavy ions tandem generators with a stripping foil are used in order to double the energy with the same high voltage. This article reviews recent developments in negative hydrogen ion sources. The underlying physics, operating parameters, and beam characteristics of selected sources will be described and compared.
Performance of the NANOGUN™ electron cyclotron resonance ion source applied for nuclear astrophysics71(2000); http://dx.doi.org/10.1063/1.1150389View Description Hide Description
A compact low-energy, high current accelerator has been constructed for the study of fusion reactions relevant to the field of nuclear astrophysics. It consists of a modified NANOGUN™, a low-energy beam transport, a windowless gas target, a beam calorimeter, and a detector system. The accelerator and the NANOGUN ion source with a single extraction electrode provides 930 μA of 20 keV at a gas target chamber. A two-electrode extraction has been tested for a few source voltages. The obtained target current is 75, 140, 110, 110, 105, 78, and 80 μA for 20, 25, 30, 35, 38, 40, and 45 kV potential, respectively. The transport efficiency from the source to the target is 5.7%.
71(2000); http://dx.doi.org/10.1063/1.1150390View Description Hide Description
The compact negative ion source having a semiplanotron discharge geometry and the two independently heated cathode inserts was developed and studied. The hot cathode insert supports discharge ignition and operation at low hydrogen pressure, while the cold one provides the glow discharge concentration in its vicinity. The stable production of beams with the current density in the emission hole in the range of about 0.1 A/cm2 was obtained in the pure hydrogen discharge. Negative ion yield at the different parts of the composite sourcecathode was measured. It was maximal in the glow region. An enhanced yield was recorded due to discharge concentration near the inserts. with a decreased work function does not produce a sizable income of surface-produced negative ions to the beam, extracted from the pure hydrogen discharge. The use of inserts as a reliable source of electrons to form the discharge simplifies the surface-plasma source use.
71(2000); http://dx.doi.org/10.1063/1.1150391View Description Hide Description
It is well known that cesium seeding in volume hydrogen negative ion sources leads to a large reduction of the extracted electron current and in some cases to the enhancement of the negative ion current. The cooling of the electrons due to the addition of this heavy impurity was proposed as a possible cause of the mentioned observations. In order to verify this assumption, we seeded the hydrogen plasma with xenon, which has an atomic weight almost equal to that of cesium. The plasma properties were studied in the extraction region of the negative ion source Camembert III using a cylindrical electrostatic probe while the negative ion relative density was studied using laser photodetachment. It is shown that the xenon mixing does not enhance the negative ion density and leads to the increase of the electron density, while the cesium seeding reduces the electron density.