44 Matching Results

Search Results

Advanced search parameters have been applied.

Beam profiles from multiple aperture sources

Description: Using a rapidly convergent approximation scheme, formulas are given for beam intensity profiles everywhere. In the first approximation, formulas are found for multiple aperture sources, such as a TFTR design, and integrated power for rectangular plates downstream for Gaussian beamlets. This analysis is duplicated for Lorentzian beamlets which should provide a probable upper bound for off-axis loading as Gaussian beamlets provide a probable lower bound. Formulas for beam intensity profiles are found everywhere. In first approximation, formulas are found for downstream intensity of multiple sources and integrated power for rectangular plates.
Date: February 1, 1979
Creator: Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Improvement of gas efficiency of negative ion sources

Description: A modification of the currently operating Calutron, magnetron, and modified duoPIGatron negative ion source is proposed. The modification should improve gas efficiency by more than an order of magnitude in the Calutron, by a factor of 5 in the magnetron, and by a factor of 2 in the duoPIGatron.
Date: August 1, 1981
Creator: Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Ion optics arithmetic and its implications for the positive ion CTR program

Description: This paper discusses ion extraction optics formulations in which presheath ionization is shown to have a negligible effect on ion optics at optimum perveance; otherwise, the examples shown establish an ionization gradient instability. Infinite slot optics as a function of perveance and potential partitioning is delineated for the TFTR tetrode from 2-D considerations; finite slot optics at optimum perveance is delineated from 3-D considerations. Finally, further 2-D considerations yield an end slot design.
Date: January 1, 1980
Creator: Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Revised Theory of Transient Mass Fluctuations

Description: Several publications during the last 10 years by Woodward and colleagues have: (1) indicated a theory based on special relativity, that predicted transient mass fluctuations; (2) cited specific embodiments where a net average force would be present; (3) suggested a few ways that this theory might be tested in the laboratory; and (4) reported such test results incorporating these embodiments, which are interpreted to support theory (1) to (3) above. In this paper we show that: (1) the average force predicted by Woodward's theory occurred only because of a neglected term in a product derivative, and that when the neglected term is correctly returned, the average force identically vanishes; (2) this vanishment of the average force occurs for arbitrary forcing functions, not just the sinusoidal one considered by Woodward; (3) the transient mass fluctuation, predicted by Woodward, was developed in a theory which neglected local gravitational forces which are several dozen orders of magnitude greater; (4) additionally considering the dominant local gravitational forces produces a vastly smaller transient mass fluctuation; (5) several inconsistencies between Woodward's referents and the development of his wave equation lead to a formulation that does not follow from the antecedents even in the absence of the demonstrations (1) to (4) above; (6) there is an alternate interpretation of the Woodward/Mahood experiments that can entirely explain the findings in terms of force contributions due to time varying thermal expansion, without invoking any general relativistic effects; and (7) a laboratory demonstration of the alternate interpretation produced 100 times the Woodward effect without resort to non-Newtonian explanations.
Date: September 4, 2001
Creator: Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Exhaust remediation using non-thermal (plasma) aftertreatments: A review

Description: There are four post combustion (nonthermal) plasma treatments on the table for reducing NOx in exhaust streams. This paper compares these techniques and suggests what appears to be a novel (8 inventions) and optimum path for development of auseful ehaust treatment system. We propose to use 5 GHz microwaves which will have a risetime of 20 ps, 100 times shorter than present state of the art and result in the best chemistry path by reduction ofplasma shielding, greater availability of atomic nitrogen, elimination of surface charging of dielectrics, avoidance of low threshold fields, and higher breakdown limit. We also propose combining a surface intrinsically into the plasma discharge. Novel embodiments are proposed for the pebbel bed discharge allowing an order of amgnitude increase of eidl-volume over the closest packing configuration.
Date: December 31, 1995
Creator: Whealton, J.H. & Graves, R.L.
Partner: UNT Libraries Government Documents Department

Beam steering due to displaced slots

Description: Using a two-dimensional algorithm, steering of triode slots was investigated for the first time with a reasonable accounting of the ion extraction sheath.
Date: September 1, 1979
Creator: Whealton, J.H.; McGaffey, R.W. & Jaeger, E.F.
Partner: UNT Libraries Government Documents Department

Electrode design and performance of the ORNL positive ion sources

Description: The neutral beam development group at ORNL has designed, constructed, and shipped four 50-kV, 100-A sources to PPPL to be used for neutral beam heating of the confined plasma on the PDX tokamak. These sources have higher current capability than scaled-down sources, and they are required to run for 0.5 s as opposed to the 0.3-s requirement for PLT and ISX-B sources. Due to an innovative electrode design, these higher power sources met these requirements and achieved a higher transmission efficiency - 76% of the total input power on target vs 60% for the original ISX-B and modified PLT sources or 40% for the original PLT sources. As a consequence, a power of 2 MW of neutrals to the torus target was achieved; this is a record for measured neutral power and exceeds that of any other power source expected to be used on such advanced tokamaks as TFTR and D-III. A theoretical consideration of the relevant Poisson-Vlasov equations for ions extracted from a plasma was used to optimize the ion optics. Using the same electrode design with a tetraode accelerating structure and a new, indirectly heated cathode, repeatable long pulse, high energy conditions of 70 kV, 7 A, 8 s and 90 kV, 9 A, 5 s were achieved. Grid deformation calculations and Monte Carlo beam line gas deposition algorithms will be discussed. A direct-magnetic-electron-blocking, direct-recovery device is described, and theoretical considerations of it are discussed.
Date: January 1, 1980
Creator: Whealton, J.H.; Gardner, W.L. & Haselton, H.H.
Partner: UNT Libraries Government Documents Department

ORNL positive ion neutral beam program

Description: The neutral beam group at Oak Ridge National Laboratory has constructed neutral beam generators for the ORMAK and PLT devices, is presently constructing neutral beam devices for the ISX and PDX devices, and is contemplating the construction of neutral beam systems for the advanced TNS device. These neutral beam devices stem from the pioneering work on ion sources of G. G. Kelley and O. B. Morgan. We describe the ion sources under development at this Laboratory, the beam optics exhibited by these sources, as well as some theoretical considerations, and finally the remainder of the beamline design.
Date: January 1, 1978
Creator: Whealton, J.H.; Haselton, H.H. & Barber, G.C.
Partner: UNT Libraries Government Documents Department

ICRF Faraday shield plasma sheath physics: The Perkins paradigm

Description: Using a 2-D nonlinear formulation which considers the plasma edge near a Faraday shield in a self consistent manner, progress is indicated in the modeling of the ion motion for a Perkins embodiment. Ambiguities in the formulation are also indicated, the resolution of which will provide significant insight into the impurities generation for ICRH antennas. 6 refs., 3 figs.
Date: January 1, 1989
Creator: Whealton, J.H.; Ryan, P.M. & Raridon, R.J.
Partner: UNT Libraries Government Documents Department

3-D analysis on arbitrarily-shaped ICRF antennas and Faraday shields

Description: Cavity antennas with Faraday shields are proposed to couple ion cyclotron radio frequency power for heating fusion plasmas. This application requires small, high-power, low-frequency antennas. The results are presented of a theoretical study of the ICRF antennas being developed for this purpose at the Radio Frequency Test Facility (RFTF). The objectives of this work are to optimize experimental designs and to confirm test results. (MOW)
Date: January 1, 1986
Creator: Chen, G.L.; Whealton, J.H.; Baity, F.W.; Hoffman, D.J. & Owens, T.L.
Partner: UNT Libraries Government Documents Department

Extraction induced emittance growth for negative ion sources

Description: Nonlinear emittance growth produced by ion extraction is considered by a 3-D analysis in a Vlasov-Poisson-Boltzmann formulation. Phenomena considered include: presheath effects, including electron depletion, electron sheath accumulation (for large transverse magnetic fields), nonlinear sheath fields (obtained by a self-consistent solution with an assumed quasi-equilibrium positive ion distribution and at least one Vlasov distribution), nonlinear fringe fields produced by the accelerator-extractor itself obtained self-consistently with item 3 above, nonlinear space charge of the beam itself, and beam in conjunction with extracted electrons. For specific volume negative ion source configurations, an investigation of the contribution of aberrations caused by an electron trap and electron accumulation in the extraction sheath are studied. Either of these effects can contribute significantly to the beam emittance, possibly dominating the contribution of the negative ion temperature in the source. 2 refs., 10 figs.
Date: January 1, 1989
Creator: Whealton, J.H.; Meszaros, P.S.; Raridon, R.I. & Rothe, K.E.
Partner: UNT Libraries Government Documents Department

Production of low energy positive ions suitable for double electron capture systems

Description: Single aperture beam extraction studies have been made of a new technique to produce low divergence beams of about 0.4/sup 0/ HWHM at about 15 keV to 40 keV. Computer calculations show that this technique of coating the plasma side of the plasma grid with about 0.01'' of Al/sub 2/O/sub 3/ can also be extended to the 0.5 keV to 5 keV range with beam optics less than 1/sup 0/. Source performance including results from multiaperture source operation will be discussed.
Date: January 1, 1977
Creator: Whealton, J H; Tsai, C C; Grisham, L R & Stirling, W L
Partner: UNT Libraries Government Documents Department

Alpha particle diagnostic beam line system to generate an intense Li/sup 0/ beam with an ORNL SITEX source

Description: The Oak Ridge National Laboratory (ORNL) SITEX (Surface Ionization with Transverse Extraction) negative ion source utilizes a 100-V/20-A reflex arc discharge in a 1300-gauss magnetic field to generate Cs+ ions and H+ or D+ ions, depending on the beam required. A shaped molybdenum plate is placed directly behind the arc column. Cesium coverage on this plate is used to minimize the surface work function, which requires two-thirds of a monolayer coverage. Cesium coverage ia adjusted both by cesium flow control into the arc discharge chamber and by temperature control of the converter using gaseous-helium cooling channels in the converter plate. Normal converter operational temperatures are 300/sup 0/ to 500/sup 0/C H/sup -//D/sup -/ beams are generated at the biased converter surface (-150 V with respect to the anode) by Cs/sup +/ sputtering of absorbed hydrogen or deuterium and by the reflection-conversion mechanism of H/sup +//D/sup +/ ions which strike the converter surface at 150 eV. The negative ions are accelerated through the 150-V plasma sheath at the converter surface and are focused by the converter geometry and magnetic field so as to pass through the exit aperture with minimum angular divergence. The ion optics of the SITEX accelerator has been calculated using the ORNL 3-D optics code and results in a divergence perpendicular to the slot of theta/sub perpendicular rms/ = 0.35/sup 0/ and parallel to the slot of theta/sub parallel rms/ = 0.18/sup 0/. This beam divergence should be adequate for injection into a radio frequency quadrupole (RFQ) for further acceleration.
Date: January 1, 1985
Creator: Dagenhart, W.K.; Stirling, W.L.; Tsai, C.C. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Toward a realistic and tractable model for negative ion extraction from volume sources

Description: A new negative ion source extraction model has been formulated and implemented that explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that (1) for high-beam currents, the beam current is limited by a transverse space charge limit, meaning that an increase in negative ion density at the extraction sheath will result in a lower beam current; (2) there is a saddle point with a potential barrier preventing most volume produced negative ions from being extracted; (3) introduction of cesium may cause an increase in the transverse space charge limit; (4) cesium also results in an increase in the fraction of volume produced negative ions which are extracted; (5) cesium may also result in reduction of extracted electrons by producing a less negative bias on the plasma electrode with respect to the plasma, thus allowing the transverse space charge limit budget to be taken up virtually totally by the ions; (6) a strong ion time scale sheath instability due to violation of the Bohm criteria produces an anomalous ion temperature which increases with beam current as routinely seen in measurements; and (7) introduction of cesium may result in a reduction in this instability. These insights may lead to improvements in volume negative ion sources.
Date: December 1, 1997
Creator: Whealton, J.H.; Olsen, D.K. & Raridon, R.J.
Partner: UNT Libraries Government Documents Department

First results from a double Vlasov model for negative ion extraction from volume sources - the possibility of an enhanced transverse space charge limit

Description: A new negative ion source extraction model has been formulated and implemented which explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that (1) for high-beam currents, the beam current is limited by a transverse space charge limit, meaning that an increase in negative ion density at the extraction sheath will result in a lower beam current (this result is universally observed at high beam currents); (2) there is a saddle point with a potential barrier preventing the most volume produced negative ions from being extracted (the combination of 1 and 2 indicates that most of the negative ions being created do not find their way into the beam); (3) introduction of cesium may cause, most importantly, an increase in the transverse space charge limit (there is an abundance of experimental data supporting this effect); (4) cesium may also result in an increase in the fraction of volume produced negative ions which are extracted; (5) cesium may also result in a reduction of extracted electrons by dint of a less negative bias on the plasma electrode with respect to the adjacent plasma, thus allowing the transverse space charge limit budget to be taken up wholly by the ions. (The combination of 3-5 represents the way an actual increase in the beam current can be achieved); (6) a strong ion time scale sheath instability due to violation of Bohm criteria produces an anomalous ion temperature that increases with beam current routinely seen in experiments; and (7) introduction of cesium may result in a reduction in this instability. These insights may lead to improvements in volume negative ion sources, and the most important finding of an increased space charge limit has apparently been verified experimentally by reinterpretation of the findings of Bacal, Allison and ...
Date: December 1, 1997
Creator: Whealton, J.H.; Olsen, D.K. & Raridon, R.J.
Partner: UNT Libraries Government Documents Department

Results from a double Vlasov model for negative ion extraction from volume sources

Description: A new negative ion source-extraction model has been formulated and implemented which explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that: (1) for high-beam currents, the beam current is limited by a transverse space-charge limit, not an emission limit; (2) there is a saddle point with a concomitant potential barrier preventing most volume produced negative ions from being extracted (the combination of 1 and 2 indicates that in some interesting cases there is the opportunity to increase extraction currents above values presently observed); (3) introduction of cesium may cause an actual increase in the transverse space-charge limit by accumulation of positive ions of cesium in the presheath.
Date: July 1, 1998
Creator: Olsen, D.K.; Raridon, R.J. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Separation of beam and electrons in the spallation neutron source H{sup {minus}} ion source

Description: The Spallation Neutron Source (SNS) requires an ion source producing an H{sup {minus}} beam with a peak current of 35 mA at a 6.2% duty factor. For the design of this ion source, extracted electrons must be transported and dumped without adversely affecting the H{sup {minus}} beam optics. Two issues are considered: (1) electron containment transport and controlled removal; and (2) first-order H{sup {minus}} beam steering. For electron containment, various magnetic, geometric and electrode biasing configurations are analyzed. A kinetic description for the negative ions and electrons is employed with self-consistent fields obtained from a steady-state solution to Poisson`s equation. Guiding center electron trajectories are used when the gyroradius is sufficiently small. The magnetic fields used to control the transport of the electrons and the asymmetric sheath produced by the gyrating electrons steer the ion beam. Scenarios for correcting this steering by split acceleration and focusing electrodes will be considered in some detail.
Date: December 1, 1997
Creator: Whealton, J.H.; Raridon, R.J. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

Separation of beam and electrons in the spallation neutron source H{sup -} ion source

Description: The Spallation Neutron Source (SNS) requires an ion source producing an H{sup {minus}} beam with a peak current of 35mA at a 6.2 percent duty factor. For the design of this ion source, extracted electrons must be transported and dumped without adversely affecting the H{sup {minus}} beam optics. Two issues are considered: (1) electron containment transport and controlled removal; and (2) first-order H{sup {minus}} beam steering. For electron containment, various magnetic, geometric and electrode biasing configurations are analyzed. A kinetic description for the negative ions and electrons is employed with self-consistent fields obtained from a steady-state solution to Poisson`s equation. Guiding center electron trajectories are used when the gyroradius is sufficiently small. The magnetic fields used to control the transport of the electrons and the asymmetric sheath produced by the gyrating electrons steer the ion beam. Scenarios for correcting this steering by split acceleration and focusing electrodes will be considered in some detail.
Date: December 1, 1997
Creator: Whealton, J.H.; Raridon, R.J. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

Increasing the Space Charge Limit and Other Effects of Cesium Seeding in Hydrogen Negative Ion Sources

Description: The role of cesium seeding in increasing the negative ion current in volume sources is described. By a reduction in the local plasma potential the current of extracted electrons is vastly reduced. As a result, cesium increases the fraction of the transverse space charge limit available to the ions by as much as a factor of three. In addition, cesium can increase the total space charge limit by injection of Cs+ into the presheath-a newly recognized phenomenon consistent with experimental measurements and determined from application of a Double-Vlasov model for negative ion extraction.
Date: September 6, 1999
Creator: Bacal, M.; Bruneteau, J.; Raridon, R.J. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Radio frequency vacuum feedthroughs for high-power ICRF heating applications

Description: Frequently, high-power pulsed ion cyclotron range of frequency experiments are limited by breakdown at the vacuum feedthrough. This paper describes the development and testing of vacuum feedthroughs to increase both reliability and capability. The ultimate goal of the program is to develop a continuous-wave feedthrough for the next generation of fusion experiments. A feedthrough concept currently under investigation consists of a simple, cylindrical alumina ceramic brazed between tapered coaxial conductors. A prototype has been tested to voltage levels in excess of 100 kV for 100-ms pulses and 70 kV for 5-s pulses at 28 MHz. Insertion-voltage-standing-wave ratios are <1.15:1 for frequencies below 450 MHz. An upgraded water-cooled version being fabricated for use on TEXTOR will be described.
Date: January 1, 1985
Creator: Owens, T.L.; Baity, F.W.; Hoffman, D.J. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

ICRF wave propagation and absorption in tokamak and mirror magnetic fields: a full-wave calculation

Description: Global solutions for the ion cyclotron resonant frequency (ICRF) wave fields in a straight tokamak with rotational transform and a poloidally symmetric mirror are calculated in the cold plasma limit. The component of the wave electric field parallel to vector Bis assumed zero. Symmetry in each problem allows Fourier decomposition in one ignorable coordinate, and the remaining set of two coupled, two-dimensional partial differential equations is solved by finite differencing. Energy absorption and antenna impedance are calculated using a simple collisional absorption model. When large gradients in vertical barBvertical bar along vectorB are present in either geometry, ICRF heating at the fundamental ion cyclotron resonance is observed. For the mirror, such gradients are always present. But for the tokamak, the rotational transform must be large enough that vectorB . delB greater than or equal to 0(1). For smaller transforms more typical of real tokamaks, only heating at the two-ion hybird resonance is observed. This suggests that direct resonant absorption at the fundamental ion cyclotron resonance may be possible in stellarators where vectorB . delB approx. 0(1) + 11.
Date: January 1, 1985
Creator: Jaeger, E.F.; Batchelor, D.B.; Weitzner, H. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department

Beam dynamics of a liquid metal ion source

Description: RMS emittance growth of liquid metal ion sources is studied. Processes included are nonlinear expansion through extractor and accelerator fringe fields, nonlinear beam space charge, plasma effects near needle, and waves (either ion-acoustic or space charge limited as considered by V.I. Dudnikov). This investigation consists of 2-D analysis of appropriate Vlasov-Poisson equations in both steady-state and time-dependent formulations. Various geometries will be considered such as some used by G. Alton of ORNL. 2 refs., 7 figs.
Date: January 1, 1989
Creator: Whealton, J.H.; Meszaros, P.S.; Rothe, K.E.; Raridon, R.J. & Ryan, P.M.
Partner: UNT Libraries Government Documents Department

Determination of fields near an ICRH antenna using a 3D magnetostatic Laplace formulation

Description: In the vicinity of an ICRH antenna strap, where there are no volume currents and a free-space wavelength is much longer then the dimensions of interest, Ampere's law reduces to a curl-free conditions on the magnetic field, allowing a magnetic scalar potential to be defined. This scalar potential is a solution of the three-dimensional (3D) Laplace equation and satisfies the following boundary conditions on the magnetic field: the line integral of the magnetic field around the current strap is equal to the current flowing in the strap and the perpendicular component of the magnetic field vanishes at conductor surfaces (no flux penetration of perfect conductors). This formulation allows for the magnetic field solution of quite complex 3D geometries, such as poloidal current straps with asymmetric radial feeds or detailed Faraday shield geometries. 5 figs.
Date: January 1, 1989
Creator: Ryan, P.M.; Rothe, K.E.; Whealton, J.H. & Swain, D.W.
Partner: UNT Libraries Government Documents Department

QUARTZ: a numerical simulation of an asymmetric electrostatic accelerator

Description: The physics and numerical aspects of the development of the computer code QUARTZ are given. This code includes the (1) use of a finite element code to obtain solutions of Poisson's equation in an asymmetric, three-dimensional volume; (2) inclusion of space charge neutralization by electrons; and (3) inclusion of ion space charge through an iterative procedure. (GHT)
Date: January 1, 1979
Creator: Wooten, J.W.; Drooks, L.J.; McCollough, D.H.; McGaffey, R.W. & Whealton, J.H.
Partner: UNT Libraries Government Documents Department