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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 -/ 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

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

Mini RF-driven ion source for focused ion beam system

Description: Mini RF-driven ion sources with 1.2 cm and 1.5 cm inner chamber diameter have been developed at Lawrence Berkeley National Laboratory. Several gas species have been tested including argon, krypton and hydrogen. These mini ion sources operate in inductively coupled mode and are capable of generating high current density ion beams at tens of watts. Since the plasma potential is relatively low in the plasma chamber, these mini ion sources can function reliably without any perceptible sputtering damage. The mini RF-driven ion sources will be combined with electrostatic focusing columns, and are capable of producing nano focused ion beams for micro machining and semiconductor fabrications.
Date: August 2, 2002
Creator: Jiang, X.; Ji, Q.; Chang, A. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

Proceedings of the workshop on ion source issues relevant to a pulsed spallation neutron source: Part 1: Workshop summary

Description: The workshop reviewed the ion-source requirements for high-power accelerator-driven spallation neutron facilities, and the performance of existing ion sources. Proposals for new facilities in the 1- to 5-MW range call for a widely differing set of ion-source requirements. For example, the source peak current requirements vary from 40 mA to 150 mA, while the duty factor ranges from 1% to 9%. Much of the workshop discussion centered on the state-of-the-art of negative hydrogen ion source (H{sup {minus}}) technology and the present experience with Penning and volume sources. In addition, other ion source technologies, for positive ions or CW applications were reviewed. Some of these sources have been operational at existing accelerator complexes and some are in the source-development stage on test stands.
Date: October 1, 1994
Creator: Schroeder, L.; Leung, K.N. & Alonso, J.
Partner: UNT Libraries Government Documents Department

Compact neutron source development at LBNL

Description: A compact neutron generator based on D-D or D-T fusion reactions is being developed at the Lawrence Berkeley National Laboratory. The deuterium or tritium ions are produced in a radio-frequency (RF) driven multicusp plasma source. Seven beamlets are extracted and are accelerated to energy of 100 keV by means of a three-electrode electrostatic accelerator column. The ion beam then impinges on a titanium coated copper target where either the 2.4 MeV D-D or 14 MeV D-T neutrons are generated by fusion reaction. The development of the neutron tube is divided into three phases. First, the accelerator column is operated at hydrogen beam intensity of 15 mA. Second phase consists of deuterium beam runs at pulsed, low duty cycle 150 mA operation. The third phase consists of deuterium or tritium operation at 1.5 A beam current. Phase one is completed and the results of hydrogen beam testing are discussed. Low duty cycle 150 mA deuterium operation is being investigated. Neutron flux will be measured. Finally the phase three operation and the advance neutron generator designs are described.
Date: July 25, 2001
Creator: Reijonen, Jani; Lou, Tak Pui; Tolmachoff, Bryan & Leung, K.N.
Partner: UNT Libraries Government Documents Department