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Review of negative ion source technology

Description: H/sup -/ or D/sup -/ ions are required for generating high energy neutral beams in heating fusion plasmas. Two distinct types of H/sup -/ ion sources can be identified: (1) surface sources - in which the H/sup -/ ions are generated by particle collisions with low work function metal surfaces; and (2) volume sources - in which the H/sup -/ ions are produced by electron-molecules and electron-ion collision processes in the volume of a hydrogen discharge. Recent experiments demonstrate that reasonable H/sup -/ ion current density can be obtained from both types of sources. However, further technology must be developed on the control of cesium and the reduction of electron drain before these sources become practical units of a multi-ampere neutral beam injection system.
Date: December 1, 1983
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

Development of high current and high brightness negative hydrogen ion sources

Description: Negative hydrogen ions have found important applications in particle accelerators and in fusion research. These ions can be generated from two different types of ion sources---the surface conversion source and the volume production source. Recent experiments demonstrate that H/sup /minus// current exceeding 1 A can be obtained from both types of ion sources. Because of the lower H/sup /minus// ion temperature and the fact that they can be operated without cesium, volume H/sup /minus// sources are highly desired. However, further technology must be developed on the control of electrons and the reduction of gas flow before this type of sources become practical units of a multiampere neutral beam injection system.
Date: April 1, 1988
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

Directly heated LaB/sub 6/ cathodes for ion source operation

Description: Some physical properties of lanthanum hexaboride ''filaments,'' when operated as cathodes in a gas discharge, are presented. These directly heated hairpin shaped filaments have been tested in different types of ion sources and are shown to be capable of long pulse or cw discharge operations. The characteristics of a shaped lanthanum hexaboride filament for the purpose of further extension of lifetime is described. The design and operation of a magnetic-field-free, directly-heated, coaxial LaB/sub 6/ cathode is also discussed.
Date: March 1, 1986
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

High-intensity sources for light ions

Description: The use of the multicusp plasma generator as a source of light ions is described. By employing radio-frequency induction discharge, the performance of the multicusp source is greatly improved, both in lifetime and in high brightness H{sup +} and H{sup {minus}} beam production. A new technique for generating multiply-charged ions in this type of ion source is also presented.
Date: October 1, 1995
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

H/sup -/ ion formation from a surface conversion type ion source

Description: Volume-produced H/sup -/ ions have been extracted from a multi-cusp ion source by using a standard extraction system. In addition, a molybdenum converter is installed in the source to generate surface-produced H/sup -/ ions. The H/sup -/ ion yield is measured by a mass spectrometer. Without cesium, the production of H/sup -/ ions by the surface process is very small compared with those generated by volume production. However, the presence of cesium can greatly enhance the surface production yield. The energy spectrum shows that the surface-generated H/sup -/ ions contain two distinct groups when cesium is added to the discharge. The energy of one group is essentially that of the sheath potential and appears to be produced by a desorption process. The second group of H/sup -/ ions have slightly higher energies and appear to be formed by a reflection process. Different types of converter materials have also been tested.
Date: October 1, 1980
Creator: Leung, K.N. & Ehlers, K.W.
Partner: UNT Libraries Government Documents Department

Negative ion formation due to hydrogen plasma surface interaction

Description: Negative ions can be produced by a desorption process when energetic positive hydrogen ions impinge on the surface of reactor walls. The relative yield of different negative ions generated from various surface materials (such as Mo, Pt, Pd, Rh, Cu, Ta, Au, C, TiC and stainless-steel) have been compared in a multicusp plasma source. The negative ions generated are self-extracted from the source, and are identified by a mass spectrometer. The total negative ion current is measured by a Faraday cup.
Date: May 1, 1984
Creator: Leung, K.N. & Ehlers, K.W.
Partner: UNT Libraries Government Documents Department

H/sup -/ production from different metallic converter surfaces

Description: The relative yield of H/sup -/ ions generated from various metallic surfaces (such as Mo, Ti, V, Nb, Pt, Pd, Rh, Cu, Ta, Al, Au and stainless steel) are compared in a multicusp source with and without the presence of cesium. Result of the investigation shows that one can optimize the H/sup -/ yield and formation process by choosing the proper converter material for a given range of source operating conditions.
Date: November 1, 1983
Creator: Leung, K.N. & Ehlers, K.W.
Partner: UNT Libraries Government Documents Department

H/sup -/ formation process in a multicusp ion source

Description: In recent years, H/sup -/ ions have been found important applications in high energy accelerators and in neutral beam heating of fusion plasmas. There are different techniques for producing the H/sup -/ or D/sup -/ ions. The most attractive scheme is the direct extraction of H/sup -/ ions from a hydrogen discharge. This technique requires no cesium and it utilizes the existing large area positive ion source technology. This paper investigates this techniques. 14 refs.
Date: July 1, 1987
Creator: Leung, K.N. & Kunkel, W.B.
Partner: UNT Libraries Government Documents Department

Operational characteristic of a compact microwave ion source

Description: A small microwave ion source has been fabricated from a quartz tube with one end enclosed by a two grid accelerator. The source is also enclosed by a cavity operated at a frequency of 2.45 GHz. Microwave power as high as 500 W can be coupled to the source plasma. The source has been operated with different geometries and for various gases in a cw mode. For hydrogen, ion current density of 200 mA/cm/sup 2/ with atomic ion species concentration as high as 80% has been extracted from the source. It has also been demonstrated that low energy oxygen ion beams (5 to 10 eV) can also be extracted from the source.
Date: March 1, 1986
Creator: Walther, S.R. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

State of H sup minus source development

Description: The status of H{sup {minus}} ion source development is reviewed. There are new and important advancement in both surface- and volume-production H{sup {minus}} sources. It is shown that high brightness H{sup {minus}} beams are generated by ion sources which utilize both surface and volume production processes. 27 refs., 6 figs.
Date: May 1, 1991
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

Volume H/sup -/ ion production experiments at LBL

Description: H/sup -/ ions formed by volume processes have been extracted from a multicusp ion source. It is shown that a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H/sup -/ ions available for extraction. A further reduction in electron current is achieved by installing a pair of small magnets at the extraction aperture. An H/sup -/ ion current density of 38 mA/cm/sup 2/ was obtained with a discharge current of approximately 350 A. Different techniques to increase the H/sup -/ ion yield have also been investigated.
Date: November 1, 1983
Creator: Leung, K.N. & Ehlers, K.W.
Partner: UNT Libraries Government Documents Department

Characteristics of a self-extraction negative ion source

Description: A multi-cusp, self-extraction, negative hydrogen ion source has been designed and constructed. Several diagnostic techniques have been applied to study the operating characteristics of this type of source. Negative H/sup -/ and D/sup -/ ions are produced on a negatively biased converter surface, and are self-extracted from the system. With the addition of cesium, the source has been operated at a neutral pressure of 1 x 10/sup -3/ Torr to generate a steady-state H/sup -/ ion current greater than 400 mA. The generation of impurity negative ions has been investigated, as have methods for reducing the presence of background electrons in the ion exit region. Plans for a larger, next-generation device will be discussed.
Date: October 1, 1980
Creator: Ehlers, K.W. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

H/sup -/ ion production from different converter materials

Description: For heating plasmas and for current drive in some fusion reactors, high energy neutral beams may be required. The high neutralization efficiency of H/sup -/ or D/sup -/ ions makes them favorable to form neutral atoms with energies in excess of 160 keV. It has been shown that a steady-state H/sup -/ ion beam with current greater than 1 A can be generated by a surface conversion type source with Mo being used as the converter material. In order to achieve the proper cesium coverage and thereby increasing the H/sup -/ ion yield, the application of porous cesium-dispensing converters is being investigated. It is also possible to optimize the H/sup -/ production by choosing the proper converter material. In this paper, we compare the negative ion yield generated by different materials (such as Mo, Ti, V, Nb, Pt, Pd, Rh, Cu, Ta, Al, Au, LaB/sub 6/ and stainless-steel) in the pure hydrogen and cesium-hydrogen modes of operation.
Date: October 1, 1984
Creator: Leung, K.N. & Ehlers, K.W.
Partner: UNT Libraries Government Documents Department

High current short pulse ion sources

Description: High current short pulse ion beams can be generated by using a multicusp source. This is accomplished by switching the arc or the RF induction discharge on and off. An alternative approach is to maintain a continuous plasma discharge and extraction voltage but control the plasma flow into the extraction aperture by a combination of magnetic and electric fields. Short beam pulses can be obtained by using a fast electronic switch and a dc bias power supply. It is also demonstrated that very short beam pulses ({approximately} 10 {micro}s) with high repetition rate can be formed by a laser-driven LaB{sub 6} or barium photo-cathode.
Date: August 1, 1996
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

Enhancement of volume H/sup /minus// production by vibrationally pre-exciting the hydrogen molecules

Description: H/sup /minus// and D/sup /minus// ions have useful applications in high-energy accelerators and in neutral beam heating, or for current drive of fusion plasmas. Among the different techniques for producing H/sup /minus// ions, direct extraction from a hydrogen discharge is the most attractive. This method requires no cesium and the H/sup /minus// ions generated by volume processes have lower average energy than those formed by surface conversion or by charge exchange processes. For this reason, intensive research and development of volume H/sup /minus// sources are now being conducted at various accelerator and fusion laboratories.
Date: February 1, 1988
Creator: Leung, K.N.; Walther, S.R. & Kunkel, W.B.
Partner: UNT Libraries Government Documents Department

Compact microwave ion source

Description: A small microwave ion source has been fabricated from a quartz tube with one end enclosed by a two grid accelerator. The source is also enclosed by a cavity operated at a frequency of 2.45 GHz. Microwave power as high as 500 W can be coupled to the source plasma. The source has been operated with and without multicusp fields for different gases. In the case of hydrogen, ion current density of 200 mA/cm/sup -2/ with atomic ion species concentration as high as 80% has been extracted from the source.
Date: May 1, 1985
Creator: Leung, K.N.; Walther, S. & Owren, H.W.
Partner: UNT Libraries Government Documents Department

A high charge state multicusp ion source

Description: Attempts have been made to generate high charge state ion beams by employing a multicusp plasma source. Three experimental investigations have been performed at LBL and at GSI to study the charge state distributions and the emittance of the extracted beam. Results demonstrate that charge state as high as +7 can be obtained with argon or xenon plasmas. The brightness of a 11 mA xenon ion beam is found to be 26 A/({pi}-mm-mrad){sup 2}. 6 refs., 6 figs.
Date: June 1, 1989
Creator: Leung, K.N. & Keller, R.
Partner: UNT Libraries Government Documents Department

Status of greater than or equal to 1 ampere H/sup -/ ion source development at the Lawrence Berkeley Laboratory

Description: This paper summarizes the effort to improve the operation of the approx. 1 A surface-production H/sup -/ ion source developed by K.W. Ehlers and K.N. Leung. The plasma chamber consists of a large magnetic bucket of oval cross section. A concave cylindrical converter surface is suspended in the plasma chamber to direct any surface-produced negative ions through the exit aperture. The ion source has been mated to a tetrode accelerator for the proof-of-principle tests. Most of the problems discovered in the tests were associated with difficulties in controlling the production process. This paper describes the plasma chamber in greater detail and illustrates the quality of the presnet ion production. The acceleration difficulties have been deferred until a better test-stand is completed.
Date: November 1, 1983
Creator: Lietzke, A.F.; Ehlers, K.W. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

Volume production of Li/sup -/ in a multicusp ion source

Description: A neutral 100kev Li beam has been used as a diagnostic tool for determining current, plasma density, and magnetic pitch angle on the Texas EXperimental Tokamak. Scale up of this diagnostic for the Tokomak Fusion Test Reactor would require use of a Li/sup -/ beam because of the inefficiency of neutralizing Li/sup +/ at the high energies required. This paper discusses effects to generate Li/sup -/ beams from a plasma discharge. 8 refs.
Date: July 1, 1987
Creator: Walther, S.R.; Leung, K.N. & Kunkel, W.B.
Partner: UNT Libraries Government Documents Department

A Sealed-Accelerator-Tube Neutron Generator for Boron Neutron Capture Therapy Application

Description: Radio-frequency (RF) driven ion sources are being developed in Lawrence Berkeley National Laboratory (LBNL) for sealed-accelerator-tube neutron generator applications. By using a 2.5-cm-diameter RF-driven multicusp source and a computer designed 100 keV accelerator column, peak extractable hydrogen current exceeding 1 A from a 3-mm-diameter aperture, together with H{sup +} yields over 94% have been achieved. These experimental findings together with recent moderator design will enable one to develop compact 14 MeV neutron generators based on the D-T fusion reaction. In this new neutron generator, the ion source, the accelerator and the target are all housed in a sealed metal container without pumping. With a 120 keV and 1 A deuteron beam, it is estimated that a treatment time of {approx} 45 minutes is needed for boron neutron capture therapy.
Date: June 1, 1998
Creator: Leung, K.-N.; Leung, K.N.; Lee, Y.; Verbeke, J.M.; Vurjic, J.; Williams, M.D. et al.
Partner: UNT Libraries Government Documents Department

Generation of oxygen, carbon and metallic ion beams by a compact microwave source

Description: A small microwave ion source fabricated from a quartz tube and enclosed externally by a cavity has been operated with different geometries and for various gases in a cw mode. This source has been used to generate oxygen ion beams with energy as low as 5.5 eV. Beam energy spread has been measured to be less than 1 eV. By installing different metal plates on the front extraction electrode, metallic ion beams such as (Be, Cu, Al, etc.) can be produced.
Date: July 1, 1986
Creator: Walther, S.R.; Leung, K.N.; Ehlers, K.W. & Kunkel, W.B.
Partner: UNT Libraries Government Documents Department