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  • 1
    Digitale Medien
    Digitale Medien
    Investigation of the electron fluid equations in a hydrodynamic model of the negative ion source : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2720-2722 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The "hydrodynamic model'' developed by Haas, Holmes, and Lea has been extended to include all elastic collision processes between the species. The properties of the electron momentum equations are investigated in detail; the solution of these equations revealing a critical point along the source axis at which the electron drift velocity reverses direction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1142834
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  • 2
    Digitale Medien
    Digitale Medien
    Intense negative ion sources at Culham Laboratory (invited) : Proceedings of the 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1153-1158 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Over the past 20 years, Culham Laboratory has been involved in the development of ion sources. Initially these were positive ion systems using magnetic multipole sources for neutral beam heating in the fusion program. However, the development of high proton yield sources with a magnetic filter at Culham has led to a major program in negative ion sources based on the so-called volume-type source which has a similar design. This work has been the basis of a range of negative ion sources for industrial, defence, and fusion applications, all of which are described. A significant part of this work lies in the basic physics of these sources, both for modeling and ion beam acceleration. Numerical models of these are presented. Recently the effects of catalysts such as cesium on the discharge has been shown to cause considerable enhancement in H− and D− yield. The cesium itself also acts as a discharge component and a large source and accelerator for a pure cesium diagnostic beam has been developed. This technique is applicable to other vapors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1145043
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  • 3
    Digitale Medien
    Digitale Medien
    Development of a high proton yield plasma source with multipole confinement and a magnetic filter (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1369-1381 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Proton yields in magnetic multipole sources can be increased by the creation of a magnetic "filter'' within the discharge volume, although this may introduce nonuniformity in the plasma. We have investigated the properties of a filter which can satisfy the requirements of plasma uniformity and discharge electrical efficiency and creates a proton yield of 87% when a 60-A beam is extracted at 80 keV. A model describing the behavior of the filter is also described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139417
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  • 4
    Digitale Medien
    Digitale Medien
    Edge effect correction for small planar Langmuir probes (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2628-2631 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: One problem inherent in the use of small planar Langmuir probes to analyze low-density plasma is expansion of the space-charge sheath with increased probe potential due to the departure from planarity caused by a nonnegligible sheath edge. Experimental evidence showing the existence of significant edge effects in the ion saturation region of the characteristic obtained from such probes is presented. The extra ion current ΔI+ collected as a result is shown to depend on the (negative) probe potential V according to the empirical relation ΔI+∝V0.75. A theoretical justification for this is obtained. Finally, the effectiveness of the technique in eliminating the edge effect for this type of probe is demonstrated by the equivalence of ion and electron densities measured in a helium discharge.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1141849
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  • 5
    Digitale Medien
    Digitale Medien
    The suppression of electrons extracted from a negative-ion source : International conference on ion sources (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 409-411 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: When a suitable accelerating voltage is applied to extract negative ions from a volume production source, electrons are also extracted. If no means of suppression is utilized, the electron current in a hydrogen plasma would typically be of the order of 80–100 times the negative-ion current. In the accelerator designs in use at Culham Laboratory, electrons entering the accelerator are dumped in a trap within the second electrode at a small fraction of the beam energy. Even using this technique, a considerable amount of power would be expended unnecessarily in accelerating electrons to the trap. The suppression of electrons at the source/accelerator interface can be achieved by means of a magnetic field applied across the extraction aperture. This traps electrons, which are then collected on an electrically biased subsection of the first electrode. Experiments performed with an electromagnet configuration have shown that the electron flux entering the accelerator can be reduced as approximately the reciprocal of the square of the magnetic field strength.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1141255
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  • 6
    Digitale Medien
    Digitale Medien
    Negative hydrogen ion extraction and electron control in a multipole ion source (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2396-2401 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A dc negative ion facility has been built to study both the mechanisms controlling H− production in multipole volume sources and the design of accelerators for negative ion beams. After a 7.5-cm movement of the extraction aperture position within the ion source, the arc current and source gas pressure were optimized, and an H− current of 10 mA was extracted from a 0.5-cm2 circular aperture in a 30-s pulse from a 100-A, 90-V discharge run at 18.8 mT. This is the first operation of such sources to provide a quasi-dc current of 20 mA cm−2. The installation of an octupole electron trap in the beam forming electrode has lowered the electron current extracted simultaneously with the H− beam by approximately a factor of 4, and this has led to a low H− beam divergence. The application of a small bias voltage of up to 2 V between the beam forming electrode and the anode has reduced this electron current still further (by more than a factor of 10) while maintaining the extracted ion current. It is now possible to extract ion currents from such a source/accelerator configuration that are larger than the accompanying electron current.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139084
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  • 7
    Digitale Medien
    Digitale Medien
    Transport of negative ions produced at a barium surface located within a multicusp ion source (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 539-546 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An experimental study on the production of negative ions at a pure barium surface mounted in a multicusp bucket source is presented. The conversion efficiency, i.e., the ratio of the extracted negative-ion current and the positive-ion current incident on the surface, for deuterium and for hydrogen, have been measured as a function of source pressure, converter bias, and distance between conversion surface and extraction aperture. The conversion efficiency for deuterium is somewhat larger when compared to hydrogen. The conversion efficiencies obtained agree with a model, taking into account the concentration of hydrogen in the barium surface layers. The cross sections which were measured for the stripping of negative ions by neutral gas agreed well with values from literature. The experimentally determined divergence of the surface-produced beam was 4.5° for hydrogen and 3.6° for deuterium at an energy of 100 eV. At a source pressure of 5 mTorr, the volume-produced negative-ion current could be enhanced by 10%; for 1 mTorr this enhancement was of the order of 25%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1140360
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  • 8
    Digitale Medien
    Digitale Medien
    Recent results on negative ion production and extraction from the Culham Ion Source Test Stand : International conference on ion sources (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 412-414 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The plasma characteristics of a volume negative ion source are described. An indirect measurement of the negative ion current density in the source has been made. Beam extraction measurements are used to attempt to verify the measurement in the source. The two are found to be in proportion. The difference between the two is briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1141256
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  • 9
    Digitale Medien
    Digitale Medien
    H− beam extraction experiments on the Culham small multipole source (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 895-901 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Beam extraction experiments have been carried out on a multicusp volume H− ion source operated in a dc mode. With an extraction aperture of 16-mm diameter, negative ion beams of up to 15 mA cm−2 have been extracted. Some experiments have been performed to investigate the physics of beam extraction from the plasma that indicate a fixed plasma boundary. The beam emittance has been measured as a function of various arc and accelerator parameters. The negative ion temperatures inferred from the emittance measurements cannot at present be explained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139799
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  • 10
    Digitale Medien
    Digitale Medien
    Extraction of H− and D− ions from a large magnetic multipole source (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 223-234 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Results are presented on the production of H− ions in a large (55×31×20 cm3) magnetic multipole discharge, which is sufficiently large to act as the plasma generator for a neutral beam injector. H− ion current densities up to 57 mA/cm2 have been extracted in pulses up to 3 s in length at low energies. When the discharge is operated in deuterium, a maximum D− current density of 27 mA/cm2 is obtained. The scaling laws of the H− production are consistent with production by dissociative attachment to rovibrationally excited molecules and loss by mutual recombination.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139312
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