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Development of H/sup -/ sources at Brookhaven National Laboratory

Description: Negative hydrogen ion sources have been developed at Brookhaven National Laboratory for several years, with the initial goal to design a source for accelerator applications and later on to design a large unit for applications in neutral beam injectors of magnetic fusion devices. Three types of sources were investigated, a hollow discharge duoplasmatron yielding H/sup -/currents up to 60 mA, a Penning source yielding H/sup -/ currents up to 440 mA, and a magnetron source yielding H/sup -/ currents up to 1 A. All sources operate with a mixture of hydrogen gas and cesium vapors, and H/sup -/ ions are most likely produced on cesium covered electrode surfaces. A larger model of a Penning/magnetron source was constructed and will be tested soon; it incorporates among other new features a system for the cooling of the cathode.
Date: January 1, 1977
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Report on the BNL H/sup -/ ion source development

Description: This paper is a report on H/sup -/ ion source development at BNL over the past ten years, with most emphasis on the selected approach for the design of a steady state operating source. Sources of this kind will be used in neutral beam lines of future fusion devices, for plasma heating and toroidal current drive. In addition to the steady state operation, H/sup -/ ion sources for this application have to show very high gas and power efficiencies. 16 references, 8 figures.
Date: January 1, 1983
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Progress in the development of H/sup -/ ion sources

Description: Charge state of an H/sup -/ ion can be changed easily by either single (neutralization) or double (ionization) electron stripping, in a very wide energy range. Development of H/sup -/ ion sources has been stimulated by several areas of application: production of high power beams of hydrogen atoms with energies of several hundred keV for plasma heating and current drive in fusion devices, production of high brightness beams of hydrogen atoms in the energy range around 100 MeV, and for use in some accelerators where H/sup -/ ions facilitate and improve the injection or ejection processes. This paper will put most emphasis on the accelerator application. Two types of sources will be considered, those where H/sup -/ ions are produced in processes on a low work function surface and those where they are produced in collisions occurring in the plasma. After a short outline of theoretical work and experimental studies of relevant processes and phenomena, a review of existing sources designs will be given, describing their performance.
Date: January 1, 1986
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Progress in the development of steady state negative ion sources for fusion applications

Description: During the past few years or so, the development of steady state sources of negative hydrogen or deuterium ions has made a substantial progress. There are several approaches under investigation, some operating with long pulses and some in a true steady state, and delivering H/sup -/ or D/sup -/ beam currents of several hundred mA up to 1 A. The improvement in the gas efficiency from a few percent for pulsed sources to the range of 5% to 15% and possibly even higher for the new sources, is another advance that was not anticipated only 4 to 5 years ago. A higher gas efficiency has come as the result of using independent plasma generation and geometrical focusing of surface produced negative ions. The power efficiency has not been changed so much, but, in a high energy system, savings of a few kW/A are less important than the reduction of the gas load. It can be expected that within five or so years a small (<1 MW) long pulse or steady state neutral beam system based on negative ions could be put into operation.
Date: January 1, 1982
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Neutral-beam system based on BNL negative-hydrogen-ion sources

Description: Parameters of the conceptual design of the BNL neutral beam system were determined as follows: beam energy, 200 keV; negative ion current, 10A; neutral beam power, 1 MW; pulse length, multisecond to steady state. The completed system study, supported by successful ion source operation at the required level, will serve to evaluate and compare different approaches in the design of a negative ion based system and, eventually, lead to the design and construction of an operational system.
Date: January 1, 1982
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Negative hydrogen ion sources for neutral beam injectors

Description: Negative ion sources offer an attractive alternative in the design of high energy neutral beam injectors. The requirements call for a single source unit capable of yielding H/sup -/ or D/sup -/ beam currents of up to 10 A, operating with pulses of 1 s duration or longer, with gas and power efficiencies comparable to or better than achievable with double electron capture systems. H/sup -/ beam currents of up to 1 A have already been achieved in pulses of 10 ms; gas and power efficiencies were, however, lower than required. In order to increase the H/sup -/ yield, extend the pulse length and improve gas and power efficiencies fundamental processes in the source plasma and on cesium covered electrode surfaces have to be analyzed; these processes will be briefly reviewed and scaling rules established. Based on these considerations as well as on results obtained with 1 A source models a larger model was designed and constructed, having a 7.5 cm long cathode with forced cooling. Results of initial tests will be presented and possible scaling up to 10 A units discussed.
Date: January 1, 1977
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Negative-hydrogen-ion sources

Description: There are two main areas of negative hydrogen ion applications: injection into high energy accelerators and production of beams of energetic hydrogen atoms for fusion devices. In both cases, the ease with which the charge state of negative ions can be changed by either single or double electron stripping is the reason that made their application attractive. In tandem accelerators, the final energy of H/sup +/ ions is twice as high as it would correspond to the terminal voltage, in circular accelerators (synchrotrons, storage rings) injection of H/sup +/ ions by full stripping of H/sup -/ ions in a foil inside the ring is not limited by the Liouville's theorem and results in a higher phase space density than achieved by direct H/sup +/ injection. Finally, beams of hydrogen atoms at energies above 100 keV, which will be required for plasma heating and current drive in future fusion devices, can efficiently be produced only by acceleration of negative ions and their subsequent neutralization.
Date: January 1, 1983
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Source options for RHIC

Description: Conceptual designs of the RHIC facility are matched to the parameters of existing tandem Van de Graaff accelerators at Brookhaven National Laboratory. It has been shown that tandems could produce many ion species up to gold with sufficient intensities for injection into the BNL booster and further acceleration and storage in AGS and RHIC synchrotrons. There have been, however, questions about the long-term performance of tandem accelerators, in view of their reliability, cost of maintenance, and expected requests for higher intensities than they could provide. A study was done in 1986 to investigate the possibility of replacing the tandems with a more compact preinjector situated close to the booster. This report will review the options for such a preinjector. 5 refs., 4 tabs.
Date: January 1, 1988
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

A volume H/sup /minus// ion source with a toroidal discharge chamber

Description: A new volume H/sup /minus// ion source has been designed with the objective to reach a current of 50 mA in 1 ms pulses, to be eventually used on the new RFQ preinjector at BNL's Alternating Gradient Synchrotron. Its main feature is a full rotational symmetry, with a toroidal discharge chamber separated from the central extraction region by a conically shaped dipole field. Preliminary studies consisted of measurements of the H/sup /minus// yield and the accompanying electron component as a function of the discharge current, discharge voltage, pressure, and extraction voltage for several geometries of the conical field; effects of the filament heating current were also studied, both for dc and ac cases. So far, it was possible to extract an H/sup /minus// current of 30 mA through an aperture of 1 cm/sup 2/, with an electron component of about 750 mA. 4 refs., 6 figs.
Date: January 1, 1989
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

BNL development of H/sup -//D/sup -/ sources for fusion reactor neutral beam lines

Description: The long range program of the BNL Neutral Beam Development Group is to design a neutral beam system based on neutralization of negative ions, with an energy of 200 keV or higher, a D/sup -/ beam current of 10 A and operating in pulses of 5 s duration or longer; the beam system would be used on fusion devices for plasma heating. Presently, work is concentrated on the development of an H/sup -/ or D/sup -/ ion source, to deliver about 1 A of beam current, at an energy of at least 10 keV and operating in pulses longer than 5 s. A source of the magnetron type was designed and fabricated and is to be tested soon; the paper describes the background experiments that were necessary for the source design, the source parameters and design features, as well as a method under consideration that would improve the gas efficiency by an order of magnitude.
Date: January 1, 1980
Creator: Prelec, K
Partner: UNT Libraries Government Documents Department

Progress in the development of high current, steady state H/sup -//D/sup -/ sources at BNL

Description: Several recent studies have shown that negative ion based neutral beam systems may become competitive at energies as low as 50 keV/nucleon. As part of its long range program, the Neutral Beam Development Group at BNL is actively engaged in the development of an H/sup -//D/sup -/ ion source capable of delivering about 1 A of beam current, at an energy of several tens of keV, operating in long pulses (5 to 30 s; thermodynamically this corresponds to a steady state operation) and having properties that would allow a scaling up to 10 A and subsequent use in a neutral beam line. Of the two models recently designed and fabricated, a Penning and a magnetron, the latter is the more promising one and efforts will be concentrated on its studies.
Date: January 1, 1980
Creator: Prelec, K
Partner: UNT Libraries Government Documents Department

Design of long pulse/steady state negative hydrogen ion sources for fusion applications

Description: By using parameters of ion sources when operating in a pulsed mode and without cooling (pulse length < 0.1 s), requirements have been determined for a long pulse (several seconds) or steady state operating mode and two sources have been designed and fabricated. First of the two is a penning source, designed for a steady state operation with a cathode power density of 1 kW/cm/sup 2/. For the range of cathode power densities between 0.2 kW/cm/sup 2/ and 1 Kw/cm/sup 2/, nucleated boiling has to be used for heat removal; below 0.2 kW/cm/sup 2/ water flow cooling suffices. Although this source should deliver 0.3 to 0.5 A of H/sup -/ ions in a steady state operation and at full power, the other source, which has a magnetron geometry, is more promising. The latter incorporates two new features compared to first designs, geometrical focusing of fast, primary negative hydrogen ions from the cathode into the extraction slit, and a wider discharge gap in the back of the source. These two changes have resulted in an improvement of the power and gas efficiencies by a factor of 3 to 4 and in a reduction of the cathode power density by an order of magnitude. The source has water cooling for all the electrodes, because maximum power densities will not be higher than 0.2 kW/cm/sup 2/. Very recently a modification of this magnetron source is being considered; it consists of plasma injection into the source from a hollow cathode discharge.
Date: January 1, 1980
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Studies of pulsed volume sources of H/sup -/ ions

Description: As part of the improvement program at the BNL Alternating Gradient Synchrotron (AGS), a new RFQ preinjector and its beam line are being assembled. While the modified H/sup -/ magnetron source of the plasma-surface type is the first choice to be used in the new preinjector, work is in progress to develop a 50 mA, low emittance volume-type H/sup -/ ion source that would not require a continuous injection of cesium vapors into the source chamber. Studies of the effect of different cusp configurations were done on a source model with a diameter of 12.5 cm and a length of 20 cm. Highest yields were obtained with linear and circular cusps, while the performance of checkerboard cusps was inferior. More than 20 mA of H/sup -/ beam current was recorded on a Faraday cup, corresponding to a current density in the extraction aperture of more than 25 mA/cm/sup 2/. A second model was then designed, constructed, and initial tests performed. It features a very low length-to-radius ratio of 0.6, cusps covering the whole discharge chamber, and the possibility to use a conical dipole field separating the outside, toroidal discharge chamber and the central extraction chamber. So far, an H/sup -/ beam current of close to 10 mA was obtained, at an arc current of 200 A. Further tests, with the objective of optimizing the magnetic field configuration, will be performed this year. 6 figs., 1 tab.
Date: January 1, 1988
Creator: Prelec, K.
Partner: UNT Libraries Government Documents Department

Intense negative hydrogen ion source for neutral injection into tokamaks

Description: In this scheme negative ions are extracted from a plasma source, accelerated to the required energy and then neutralized by stripping in a gas, metal vapor or plasma jet. One of the most promising direct extraction sources is the magnetron source, operating in the mixed hydrogen-cesium mode. In the present source cathode current densities are up to 20 A/cm$sup 2$ at arc voltages between 100 V and 150 V. In order to utilize the discharge more efficiently multislit extraction geometry was adopted. Highest currents were obtained by using six slits, with a total extraction area of 1.35 cm$sup 2$. At an extraction voltage of 18 kV negative hydrogen ion currents close to 1 A were obtained, which corresponds to current densities of about 0.7 A/cm$sup 2$ at the extraction aperture. Pulse length was 10-20 ms and the repetition rate 0.1 Hz. The total extracted current was usually 2-3 times the H$sup -$ current. (auth)
Date: January 1, 1975
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department

BNL neutral beam development group. Progress report, FY 1979

Description: The objective of the BNL Neutral Beam Program is to develop a 250 keV neutral beam system suitable for heating experiments in toroidal or mirror plasma devices. The system will be based on acceleration and neutralization of negative hydrogen ions produced in and directly extracted from a source. The objective of source studies is to develop a unit delivering 10 A of negative ion currents in pulses of 1 s duration or longer, operating with extracted current densities of at least 0.5 A/cm/sup 2/ and having acceptable power and gas efficiencies and good beam optics. The 250 keV accelerator development work covers different structures, including those separated from the source by a bending magnet or a beam transfer system. During FY 1979 substantial progress was achieved toward the objectives of the program; in the same period the BNL program was reviewed by a panel, resulting in suggestions for a better orientation toward prospective users' requirements and in establishment of contacts with Princeton Plasma Physics Laboratory (TFTR Project) and Lawrence Berkeley and Livermore Laboratories (MFTF Project). A cooperative effort with Westinghouse was initiated in the second half of FY 1979 in order to utilize industrial facilities and expertise.
Date: January 15, 1980
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department

BNL Neutral-Beam Development Group. Progress report FY 1981

Description: The Brookhaven High Energy Neutral Beam Development Group is developing injector systems, particularly for the next generation of fusion mirror and tokamak experiments. These injectors are based on the acceleration and neutralization of negative deuterium ions, to utilize their high neutralization efficiency which is nearly independent of energy above 50 keV/nucleon.
Date: January 15, 1982
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department

BNL neutral-beam development group. Progress report FY 1982

Description: Efforts were concentrated on the development of H/sup -//D/sup -/ sources capable of delivering about 1A of beam current, operating steady state at an energy of several tens of keV and having properties that would allow a scaling up to 10A and their use in a high energy neutral beam line. In the seventies we have developed negative ion sources of the plasms surface type with extracted current densities of several hundred mA/cm/sup 2/. Particularly successful was the development of the magnetron source, from which pulsed beam currents in excess of one ampere have been obtained and accelerated up to 120 kV. These magnetrons have become standard sources in high energy accelerator laboratories around the world and they are candidates for application in polarized H/sup -/ ion sources as well. Work on hollow cathode deuterium sources and neutraizers is reported.
Date: January 17, 1983
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department

BNL neutral beam development group. Progress report FY 1980

Description: The objective of the BNL Neutral Beam Program is to develop a 250 keV neutral beam system suitable for heating and other experiments in toroidal or mirror plasma devices. The system is based on acceleration and neutralization of negative hydrogen ions produced in and directly extracted from a source. The objective of source studies is to develop a module delivering 10 A of negative ion currents, with pulse lengths ranging from several seconds duration up to a steady-state operation. The extracted current density should be several hundred mA/cm/sup 2/, and the source should operate with power and gas efficiencies acceptable from the beam line point of view. The objective of beam extraction and transport studies is to design a system matching the 10 A source module to the acceleration stage. The 250 keV acceleration studies cover several options, including a d.c. close-coupled system, a large aperture d.c. system matched to the source by a bending magnet, a multiaperture d.c. system following a multiaperture strong focusing transport line, and a MEQALAC structure.
Date: January 15, 1981
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department

BNL Neutral Beam Development Group. Progress report, FY 1983 and final report

Description: The BNL Neutral Beam Development Group has been active in the program for the development of high energy, high power neutral beam systems since 1973. These injectors are based on the production, acceleration and neutralization of negative hydrogen or deuterium ions and are supposed to be used for plasma heating and current drive in the next generation of fusion devices. Over the span of 10 years the group has studied plasma-surface type of negative hydrogen ion sources, transport and acceleration of negative ion beams and neutralization of negative ions in gases and plasmas. As the required source parameters (current, pulse length, efficiency) were changing over this period of time, the group developed several types of sources, resulting finally in the design of a steady state device operating with an excellent gas efficiency and having the possibility of scaling-up to the size necessary for a high power neutral beam system. The funding of this program was, however, terminated in FY 83 before the neutral beam performance of the source could be shown. This report will present a summary of the BNL effort over the past ten years, with most emphasis on achievements in FY 83, including the description of the 2 A steady state H/sup -/ or D/sup -/ ion source for use in a neutral beam line and of the plasma neutralizer capable to achieve neutralization efficiencies above 80%.
Date: March 16, 1984
Creator: Prelec, K. & Sluyters, T.
Partner: UNT Libraries Government Documents Department