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Negative lithium emission from a tungsten surface in a plasma

Description: Three possibilities for making Li/sup -/ ions have been considered: electron capture in a suitable gas or vapor, extraction from a lithium plasma, and production on a low work function surface in a plasma. The only quantitative results, so far, have been for electron capture, with the highest yield being about 5% for Li/sup +/ in Cs vapor at 5 keV. Of the other two methods, Leung has seen some Li/sup -/ produced in the volume of a plasma, and we now report the observation of Li/sup -/ from a surface in a He-Li plasma.
Date: October 1, 1984
Creator: Stearns, J.W. & Pyle, R.V.
Partner: UNT Libraries Government Documents Department

H/sup -/ production from partially cesiated surfaces in the presence of a hydrogen plasma

Description: A large source employing a magnetic bucket geometry with a large curved converter surface focused on a single slit extractor is presently being studied at LBL. In order to understand the relationships among the Cs coverage, the high energy (back-scattered) and low energy (desorbed) H/sup -/ beams and the angular and energy distributions of the beams, we have constructed a small version of the LBL source in which the work function of the converter, which is immersed in the plasma (n < 10/sup 11//cm/sup 3/), can be measured by photo emission while the other parameters are varied. In addition, the converter can be rotated and the H/sup -/ beam collimated and analyzed to give a complete energy and angular spectrum.
Date: November 1, 1983
Creator: Wada, M.; Pyle, R.V. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

A neutral-beam diagnostic for fast confined alpha particles in a burning plasma: Application on CIT (Compact Ignition Tokamak)

Description: Diagnostic methods for fast confined alpha particles are essential for a burning-plasma experiment. We review one- and two-electron-capture methods using energetic neutral beams, and provide quantitative estimates of signal level for a two-electron-capture method applicable to CIT. The best probe is a ground-state helium-atom beam because of its relatively good penetration into a CIT plasma and the large cross section for two-electron capture; it can be produced in useful quantities from HeH/sup +/. We calculate a signal level of the order of 10/sup 7/ counts/s for 100 mA of accelerated HeH/sup +/, which is sufficient to allow time-resolved measurements of the alpha-particle velocity distribution. Limited position information could be obtained for appropriate access port geometry. This diagnostic is feasible, and we recommend further research and development leading to implementation on CIT. 39 refs., 16 figs., 5 tabs.
Date: October 1, 1987
Creator: Schlachter, A.S.; Stearns, J.W. & Cooper, W.S.
Partner: UNT Libraries Government Documents Department

Work function dependence of surface produced H/sup -/ in the presence of a plasma

Description: The maximum H/sup -/ flux from a netatively biased converter cathode occurs at the work function minimum. A cesiated hydrogen plasma produces a partially-cesiated surface at the converter. The cesium coverage can be be controlled by the cesium partial pressure, the bias on the converter and the plasma density, while the work function of the converter surface is measured by the photo-electric effect, using a bright light source and a series of filters. The angular dependence is measured by rotating the converter.
Date: November 1, 1983
Creator: Wada, M.; Pyle, R.V. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

Neutral-beam design options. [Design and cost optimization]

Description: The designs and costs of magnetic-confinement experimental devices and reactors can be affected strongly by the choice of parameters for the neutral-beam injection system. To provide the designer with information with which to estimate the physical and cost consequences of variations in energy, neutralizer thickness, ion-species mixtures, etc., we are carrying out parametric studies of the neutralization efficiency. Some of the results are reported here. The data base is too small and uncertain to permit calculations which would optimize all aspects of designs at this time.
Date: April 1, 1976
Creator: Stearns, J. W.; Berkner, K. H. & Pyle, R. V.
Partner: UNT Libraries Government Documents Department

Negative-hydrogen-ion production by backscattering from alkali-metal targets

Description: Measurements have been made of the total backscattered D/sup -/ and H/sup -/ yields from Cs, Rb, K, Na and Li surfaces bombarded with D/sub 2//sup +/, D/sub 3//sup +/, H/sub 2//sup +/ and H/sub 3//sup +/ in the energy range 0.15 to 4 keV/nucleus. All measurements were made at a background pressure less than 10/sup -9/ Torr and the alkali-metal surfaces were evaporated onto a substrate in situ to minimize contamination of surfaces. For each target, the D/sup -/ and H/sup -/ yields exhibited maxima (as high as 8% per incident deuteron or proton for Cs); the maxima occurred at incident energies between 300 and 1000 eV/nucleus and always occurred at a lower incident energy for H than for D for a given target. Both the H/sup -/ and D/sup -/ yields decreased, at any measured energy, in going from Cs to Li in the order given above. Measurements of the H/sup -/ yield were also made for H/sub 3//sup +/ bombarding a W substrate, as a function of the work function of the target, as Li was deposited on the W. The work function of the target showed a minimum as the Li coverage was increased and the H/sup -/ yield showed a corresponding maximum which was almost two orders of magnitude higher than the H/sup -/ yield for a thick Li target.
Date: November 1, 1979
Creator: Schneider, P.J.; Berkner, K.H.; Graham, W.G.; Pyle, R.V. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

Neutralization of a fast negative-ion beam

Description: Neutralization of a fast negative-ion beam, primarily H/sup -/, is discussed in terms of competing one- and two-electron detachment processes in a variety of media: gas (vapor), plasma, liquid sheet, solid foil.
Date: January 1, 1986
Creator: Schlachter, A.S.; Mowat, J.R.; Stearns, J.W.; Gohil, P. & Pyle, R.V.
Partner: UNT Libraries Government Documents Department

D- PRODUCTION BY CHARGE TRANSFER OF 0.3-10 keV D+, D0, AND D- IN CESIUM, RUBIDIUM, AND SODIUM VAPOR TARGETS

Description: Equilibrium charge-state fractions for 0.3-10-keV D ions and atoms in cesium-, rubidium-, and sodium-vapor targets are reported. The D{sup -} yield from charge transfer in a thick cesium-vapor target exceeds 30 percent at energies below 800 eV. The high D{sup -} yield in cesium vapor is consistent with recent calculations of the cross sections {sigma}{sub 0-} and {sigma}{sub -0} at low energies; at energies above 2.5 keV, the D{sup -} yield is consistent with our measurements of {sigma}{sub 0-} and {sigma}{sub -0}. The D{sup -} yield from charge transfer in rubidium vapor is similar to that for cesium vapor. For sodium vapor, however, there is a broad maximum of about 10 percent D{sup -} yield at about 3 keV, with slight structure at lower energies, implying structure in one of the charge-transfer cross sections.
Date: April 1, 1980
Creator: Schlachter, A.S.; Stalder, K.R. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

A high-charge-state plasma neutralizer for an energetic H/sup -/ beam

Description: A high-charge-state plasma neutralizer for a beam of energetic H/sup -/ ions offers the potential of high optimum neutralization efficiency (approx.85%) relative to a gas target (50 to 60%), and considerably reduced target thickness. We have calculated cross sections for charge-changing interactions of fast H/sup -/ and H/sup 0/ in collision with highly charged ions using a semiclassical model for H/sup -/, and the Classical-Trajectory Monte Carlo method plus Born calculations, to obtain correct asymptotic cross sections in the high-energy limit. Charge-state fractions as a function of plasma line density, and f/sub 0//sup max/, the maximum H/sup 0/ fraction, are calculated using these cross sections; we find that f/sub 0//sup mx/ approx. = 85% for ion charge states in the range 1+ to 10+, and that target ion line density for f/sub 0//sup max/ decreases approximately as the square of the plasma ion charge state. The maximum neutral fraction is also high for a partially ionized plasma. We have built a small multicusp plasma generator to use a a plasma neutralizer; preliminary results show that the plasma contains argon ions with an average charge state between 2+ and 3+ for a steady-state discharge.
Date: October 1, 1986
Creator: Schlachter, A. S.; Leung, K. N.; Stearns, J. W. & Olson, R. E.
Partner: UNT Libraries Government Documents Department

Photoelectric work function measurement of a cesiated metal surface and its correlation with the surface-produced H/sup -/ ion flux

Description: For application in plasma heating, fueling, and current drive of magnetic fusion devices, high current negative deuterium ion sources for intense neutral beam injectors are being developed using efficient production of negative hydrogen isotope ions on low work function metal surfaces imbedded in hydrogen plasmas. In order to investigate the correlation between work function and negative hydrogen ion production, photoelectron emission from a cesiated metal surface, which is immersed in a hydrogen plasma with an electron density less than 5 x 10/sup 10//cc, was measured in the photon energy range of 1.3 to 4.1 eV. The work function determination was based on Fowler's analysis, and at the optimum coverage a work function of less than 1.5 eV was observed for a Cs-Cu surface. Measured values of work functions for different Cs coverages were compared to the negative hydrogen currents produced at the metal surface in the discharge; the surface production of negative hydrogen ion current is monotonically increasing with decreasing work function.
Date: September 1, 1982
Creator: Wada, M.; Berkner, K.H.; Pyle, R.V. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

D- production by backscattering from clean alkali-metal surfaces

Description: Measurements have been made of the total back-scattered D/sup -/ yields from Cs, Rb, K, Na and Li surfaces bombarded with D/sub 2//sup +/ and D/sub 3//sup +/ in the energy range 0.05 to 3.5 keV/nucleon. All measurements were made at a background pressure less than 10/sup -9/ Torr and the alkali-metal surfaces were evaporated onto a substrate in situ to assure uncontaminated surfaces. For each target, the D/sup -/ yield is at a maximum (as high as 12% per incident deuteron for Cs) between 150 and 300 eV/nucleon, and at any measured energy, the D/sup -/ yield decreases from Cs to Li in the order given above.
Date: September 1, 1977
Creator: Schneider, P. J.; Berkner, K. H.; Graham, W. G.; Pyle, K. V. & Stearns, J. W.
Partner: UNT Libraries Government Documents Department

Collisional pumping for the production of intense spin-polarized neutral beams: target considerations. Revision

Description: Polarized beams at intensity levels heretofore not considered feasible have recently been proposed for heating and fueling fusion plasmas. Polarized-beam fueling could increase fusion rates by 50% as well as allow control of the directionality of the fusion products. A process which we have recently described, and called collisional pumping, promises to produce beams of polarized ions vastly more intense than producible by current methods.
Date: April 1, 1985
Creator: Stearns, J.W.; Burrell, C.F.; Kaplan, S.N.; Pyle, R.V.; Ruby, L. & Schlachter, A.S.
Partner: UNT Libraries Government Documents Department

Electron-spin-polarized targets for a collisionally-pumped polarized-ion source

Description: Collisional pumping has been proposed as a mechanism for producing polarized ion beams more intense by orders of magnitude than those from the best existing sources. One implementation of this method employs a very thick electron-spin-polarized alkali-vapor target in a low magnetic field, and is characterized by a predicted 100% spin-transfer efficiency from the target to the beam. Target characteristics and design constraints are discussed.
Date: May 1, 1985
Creator: Kaplan, S.N.; Burrell, C.F.; Pyle, R.V.; Ruby, L.; Schlachter, A.S. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

Collisional pumping for the production of intense spin-polarized, neutral beams: target considerations

Description: We have recently proposed a new method for the production of nuclear-spin-polarized ions and atoms. A fast beam of atoms is pumped to a single spin state by means of successive capture of a spin-polarized electron followed by the loss of an electron, in a highly electron-spin-polarized medium. This process, which we call collisional pumping, is characterized by the transfer of the electron spin to the nucleus through hyperfine interactions whenever the atom is in a neutral state. We anticipate that fast polarized beams of 1A or more can be produced, with possible applications to accelerators and fusion research. This process can be accomplished by passage of a low-energy (approx. 1 keV/u) H/sup +/ (D/sup +/,T/sup +/) beam through a polarized alkali-metal-vapor target of about 10/sup 16/ electron-spin-polarized atoms/cm/sup 2/. The only bound state of a negative hydrogen ion is a singlet state, which provides a selection mechanism by making electron attachment impossible when the projectile and target electrons have the same spin.
Date: October 1, 1984
Creator: Stearns, J.W.; Burrell, C.F.; Kaplan, S.N.; Pyle, R.V.; Ruby, L. & Schlachter, A.S.
Partner: UNT Libraries Government Documents Department

Conceptual design of a neutral-beam injection system for the TFTR

Description: The neutral-beam injection requirements for heating and fueling the next generation of fusion reactor experiments far exceed those of present devices; the neutral-beam systems needed to meet these requirements will be large and complex. A conceptual design of a TFTR tokamak injection system to produce 120 keV deuterium-ion beams with a total power of about 80 MW is given. (auth)
Date: November 1, 1975
Creator: Ehlers, K.W.; Berkner, K.H.; Cooper, W.S.; Hooper, E.B.; Pyle, R.V. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

Collisional pumping in polarized sodium vapor

Description: Collisional pumping has been proposed as a mechanism for efficient transfer of spin from an electron-spin-polarized target to the nuclei of a fast atom or ion beam. Collisional pumping takes place in low magnetic fields, can give polarization transfer approaching 100%, and offers the potential for producing polarized beams orders of magnitude more intense than presently achieved. Recently reported calculations of electronic spin-exchange cross sections at useful ion-source energies suggest significantly greater rates of pumping than first estimated, and give cause for increased optimism about sucessful implementation. Collisional pumping is described, and beam characteristics are given for prototype polarized source parameters.
Date: January 1, 1986
Creator: Kaplan, S.N.; pyle, R.V.; Ruby, L.; Schlachter, A.S.; Stearns, J.W. & Anderson, L.W.
Partner: UNT Libraries Government Documents Department

Design data for calculating neutral beam penetration into Z/sub eff/ > 1 plasmas

Description: Impurities such as C, N, O, Fe, and Mo in a confined plasma reduce the penetration of the energetic neutral deuterium or hydrogen beam injected for heating or fueling the plasma, thus affecting the energy- and fuel-deposition profiles. New calculations, confirmed by recent experimental results, show that previous estimates of the reduction of neutral beam penetration due to impurities in the plasma were overly pessimistic. Until recently, the cross sections used to calculate beam attenuation had been assumed to be q/sup 2/times the cross section for H/sup +/ + H obtained from the Born approximation, where q is the charge state of the ion. This led to very large cross sections for large values of q, and thus to very stringent requirements on the acceptable level of impurity ions in the plasma.
Date: January 1, 1978
Creator: Olson, R.E.; Berkner, K.H.; Graham, W.G.; Pyle, R.V.; Schlachter, A.S. & Stearns, J.W.
Partner: UNT Libraries Government Documents Department

Atomic hydrogen density measurements in an ion source plasma using a vacuum ultraviolet absorption spectrometer

Description: A system to determine the density and temperature of ground state hydrogen atoms in a plasma by vacuum ultraviolet laser absorption spectroscopy is described. The continuous tunability of the spectrometer allows for analysis at any of the Lyman transitions. The narrow bandwidth of the laser system allows for the accurate determination of the absorption lineshape and hence the translational temperature. The utility of the system is exemplified by data obtained on an ion-source plasma. The measurements demonstrate the quality of the data as well as illustrating the behavior of this ion source under varying discharge conditions. 9 refs., 5 figs., 1 tab.
Date: January 1, 1989
Creator: Stutzin, G.C.; Young, A.T.; Schlachter, A.S.; Stearns, J.W.; Leung, K.N.; Kunkel, W.B. et al.
Partner: UNT Libraries Government Documents Department

Measurement of H and H/sub 2/ populations in-situ in a low-temperature plasma by vacuum-ultraviolet laser-absorption spectroscopy

Description: A new technique, vacuum-ultraviolet laser-absorption spectroscopy, has been developed to quantitatively determine the absolute density of H and H/sub 2/ within a plasma. The technique is particularly well suited to measurement in a plasma, where high charged particle and photon background complicate other methods of detection. The high selectivity and sensitivity of the technique allows for the measurement of the rotational-vibrational state distribution of H/sub 2/ as well as the translational temperature of the atoms and molecules. The technique has been used to study both pulsed and continuous H/sup /minus// ion-source plasma discharges. H/sub 2/ state distributions in a multicusp ''volume'' H/sup /minus// ion- source plasma show a high degree of internal excitation, with levels up to v = 5 and J = 8 being observed. The method is applicable for a very wide range of plasma conditions. Emission measurements from excited states of H are also reported. 17 refs., 9 figs.
Date: December 1, 1988
Creator: Schlachter, A.S.; Young, A.T.; Stutzin, G.C.; Stearns, J.W.; Doebele, H.G.; Leung, K.N. et al.
Partner: UNT Libraries Government Documents Department

Development of 120 keV neutral beam injectors

Description: Recent development efforts on 120-keV ion sources for neutral-beam systems for the fusion program have focused on producing pulse-lengths longer than the 0.5-sec originally specified for TFTR and improvement of the atomic-ion fraction of the beam. From heat-load measurements of the accelerator grids we deduce that our edge cooled grids should be capable of operation for pulse lengths of the order of 2 seconds; we have operated our 8- x 10-cm accelerator for 1.5-seconds and have fabricated a water-cooled accelerator for longer pulse operation. A multi-cusp ion source has been used to produce 65A beams with D/sup +/ fractions of about 75%.
Date: November 1, 1979
Creator: Berkner, K.H.; Burrell, C.F.; Cooper, W.S.; Ehlers, K.W.; Lietzke, A.F.; Owren, H.M. et al.
Partner: UNT Libraries Government Documents Department

H/sup -/ and D/sup -/ production by backscattering from surfaces

Description: Three experiments are described in which H/sup -/ or D/sup -/ ions have been produced by backscattering from surfaces coated with alkali metals: (1) Backscattering of H/sup -/ and D/sup -/ produced by 0.15- to 4-keV/nucleus H/sub 2//sup +/, H/sub 3//sup +/, D/sub 2//sup +/, and D/sub 3//sup +/ bombarding clean targets of Cs, Rb, K, Na, and Li. For each target, the H/sup -/ and D/sup -/ yields were maximized at incident energies between 300 and 1200 eV/nucleus and always at a lower incident energy for H than for D on a given target. At any given incident energy, both the H/sup -/ and D/sup -/ yields decreased in going from Cs to Li in the order given above. (2) A Mo surface was bombarded by a low-energy flux of H atoms produced in a tungsten furnace. As the surface work function was reduced by evaporating Cs onto the target, a small fraction (10/sup -9/) of the incident hydrogen atoms was observed as backscattered H/sup -/ ions. (3) Surfaces of Mo, W, Pt, Ni, Cu, Re, Ta, and Pd were bombarded by hydrogen ions produced in a discharge. Two classes of H/sup -/ ions were observed when Cs was added to the discharge - H/sup -/ ions leaving the surface with approximately < 10 eV and H/sup -/ ions leaving the surface with approximately 50 to 100 eV.
Date: April 1, 1981
Creator: Berkner, K.H.; Ehlers, K.W.; Graham, W.G.; Leung, K.N.; Pyle, R.V.; Schneider, P.J. et al.
Partner: UNT Libraries Government Documents Department

Neutral-beam research and development at LBL, Berkeley

Description: The neutral-beam research and development effort at LLL has been concerned mainly with design, construction, and testing of ion sources needed in present and planned experiments, chiefly at LLL. Development of techniques for producing reactor-type neutral beam systems with higher voltage, current, and duty cycle proceeds as resources permit. An important part of this program is the attempt to increase the physics understanding and technology needed for the design of beams with precisely controlled trajectories, e.g., converging beams. (auth)
Date: November 1, 1973
Creator: Baker, W.R.; Berkner, K.H.; Cooper, W.S.; Ehlers, K.W.; Kunkel, W.B.; Pyle, R.V. et al.
Partner: UNT Libraries Government Documents Department