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Improved field stability in RFQ structures with vane-coupling rings

Description: The small apertures common in many RFQ linac designs lead to tuning difficulties, primarily because asymmetries in the quadrant fields can arise as a result of small non-uniformities in the vane-to-vane capacitances. Sensitivity to such capacitance or other tuning variation in the quadrants is greatly reduced by the introduction of pairs of vane-coupling rings that provide periodic electrical connections between diametrically opposite vanes. Results of measurements on a cold model RFQ structure with and without vane-coupling rings are presented. The number of rings required for field stabilization and the effect of rings on mode frequencies are discussed.
Date: March 1, 1983
Creator: Schneider, H.R. & Lancaster, H.
Partner: UNT Libraries Government Documents Department

Initial operation of the LBL heavy ion RFQ

Description: The LBL heavy ion RFQ accelerator, a 200 MHz structure that accelerates an ion with q/A greater than or equal to 1/7 from 8.4 to 200 keV/n, has now passed all its acceptance tests. This machine is unique in several respects: it uses coupling rings between vanes to stablize the azimuthal field distribution, it incorporates a vane mounting system that simplifies vane alignment, it uses no end tuners or power distribution manifold, and it needs only one rf feed loop. The beam performance of this machine is reported in this paper.
Date: August 1, 1983
Creator: Staples, J.; Gough, R.; Schneider, H. & Zajec, E.
Partner: UNT Libraries Government Documents Department

Vane-coupling rings simplify tuning of the LBL RFQ accelerator

Description: A new heavy ion RFQ accelerator has been commissioned as part of a Bevalac injector upgrade project. This RFQ is the first four vane type to incorporate vane coupling rings (VCR's) as part of the structure. This paper reports on the simplified tune up procedure made possible by the use of VCR's including field flattening, end tuning, and frequency adjustment. Also included is a discussion of high power performance including conditioning.
Date: August 1, 1983
Creator: Lancaster, H.; Gough, R.; Howard, D. & Schneider, H.R.
Partner: UNT Libraries Government Documents Department


Description: The oxidation of Hg in HNC/sub 3/ was investigated. An empirical rate law, oxidation rates, and Hg species in solution were determined. A reaction mechanism based on the presence of nitrous acid can be interpreted in terms of the rate expression derived. (auth)
Date: November 30, 1957
Creator: Murray, R.F. & Schneider, H.
Partner: UNT Libraries Government Documents Department

Investigation of the effect of natural phenomena and industrial activity on stratospheric ozone trends. Final report, September 1993--June 1998

Description: The long term goal of this work is to separate the effects of natural variability and anthropogenic emissions on the chemical composition of the atmosphere. In particular, the authors are concerned with the variability of ozone in the stratosphere and the supply of ozone from the stratosphere to the upper troposphere. During the first phase of this project the authors developed an interactive two-dimensional (2D) model of the dynamics, radiation, and chemistry of the stratosphere. The most important features of the model are the use of the full primitive equations in two dimensions, small horizontal mixing in the tropical regions and small mechanical damping in the lower stratosphere. As a result, transport in the tropics and the mass exchange between the tropics and midlatitude are controlled advectively.
Date: December 1, 1998
Creator: McElroy, M.B. & Schneider, H.R.
Partner: UNT Libraries Government Documents Department

The ISAC Project at TRIUMF

Description: Development of a facility combining an isotope-separator-on-line (ISOL) with a post-accelerator, to produce energetic ion beams far from the valley of nuclear stability, was originally proposed for installation on one of the beam lines of the TRIUMF cyclotron about ten years ago. A test facility (TISOL) consisting of a target, ion source, and mass separator, but without a post accelerator, was subsequently installed and has been in use to support an experimental program and to aid in development of target/ion source systems. The facility is currently being augmented with the addition of a laser neutral atom trap for a proposed series of {beta} decay and atomic parity non-conservation experiments, using selected radioactive alkali isotopes, to test some symmetry properties of the Standard Model. In addition, work has begun on a new upgraded facility consisting of remotely handleable target/ion source assemblies, a new mass separator with resolution m/{Delta}m = 10,000, and post-acceleration to 1.5 MeV/u, for ions with A {le} 30.
Date: September 1, 1995
Creator: Schneider, H.R.
Partner: UNT Libraries Government Documents Department

Growth and Characterization of Quantum Dots and Quantum Dots Devices

Description: Quantum dot nanostructures were investigated experimentally and theoretically for potential applications for optoelectronic devices. We have developed the foundation to produce state-of-the-art compound semiconductor nanostructures in a variety of materials: In(AsSb) on GaAs, GaSb on GaAs, and In(AsSb) on GaSb. These materials cover a range of energies from 1.2 to 0.7 eV. We have observed a surfactant effect in InAsSb nanostructure growth. Our theoretical efforts have developed techniques to look at the optical effects induced by many-body Coulombic interactions of carriers in active regions composed of quantum dot nanostructures. Significant deviations of the optical properties from those predicted by the ''atom-like'' quantum dot picture were discovered. Some of these deviations, in particular, those relating to the real part of the optical susceptibility, have since been observed in experiments.
Date: April 1, 2003
Partner: UNT Libraries Government Documents Department

Simulation of Diffusive Lithium Evaporation Onto the NSTX Vessel Walls

Description: A model for simulating the diffusive evaporation of lithium into a helium filled NSTX vacuum vessel is described and validated against an initial set of deposition experiments. The DEGAS 2 based model consists of a three-dimensional representation of the vacuum vessel, the elastic scattering process, and a kinetic description of the evaporated atoms. Additional assumptions are required to account for deuterium out-gassing during the validation experiments. The model agrees with the data over a range of pressures to within the estimated uncertainties. Suggestions are made for more discriminating experiments that will lead to an improved model.
Date: December 9, 2010
Creator: Stotler, D. P.; Skinner, C. H.; Blanchard, W. R.; Krstic, P. S.; Kugel, H. W.; Schneider, H. et al.
Partner: UNT Libraries Government Documents Department

RFQ development at LBL

Description: The radio frequency quadrupole (FRQ) is a structure which can efficiently focus, bunch and accelerate low velocity ion beams. It has many features which make it particularly attractive for applications in the biomedical and nuclear sciences. There are two projects in progress at LBL where the incorporation of heavy ion RFQ technology offers substantial benefits: in the upgrade of the Bevatron local injector, and in the design of a dedicated heavy ion medical accelerator. In order to meet the requirements of these two important applications, a 200 MHz RFQ structure has been designed for ions with charge to mass ratios as low as 0.14, and a low rf power scale model has been built and tested. Construction of the high power model has begun. The status of this project is reviewed and a summary of technical specifications given.
Date: November 1, 1982
Creator: Abbott, S.; Brodzik, D.; Gough, R.A.; Howard, D.; Lancaster, H.; MacGill, R. et al.
Partner: UNT Libraries Government Documents Department

Improvement in Plasma Performance with Lithium Coatings in NSTX

Description: Lithium as a plasma-facing material has attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Dramatic effects on plasma performance with lithium-coated plasma-facing components (PFCOs) have been demonstrated on many fusion devices, including TFTR, [1] T-11M, [2] and FT-U. [3] Using a liquid-lithium-filled tray as a limiter, the CDX-U device achieved very significant enhancement in the confinement time of ohmically heated plasmas. [4] The recent NSTX experiments reported here have demonstrated, for the first time, significant and recurring benefits of lithium PFC coatings on divertor plasma performance in both L- and H- mode regimes heated by neutral beams.
Date: September 12, 2008
Creator: Kaita, R; Ahn, J -W; Allain, J P; Bell, M G; Bell, R; Boedo, J et al.
Partner: UNT Libraries Government Documents Department

Transition to ELM-free Improved H-mode by Lithium Deposition on NSTX Graphite Divertor Surfaces

Description: Lithium evaporated onto plasma facing components in the NSTX lower divertor has made dramatic improvements in discharge performance. As lithium accumulated, plasmas previously exhibiting robust Type 1 ELMs gradually transformed into discharges with intermittent ELMs and finally into continuously evolving ELM-free discharges. During this sequence, other discharge parameters changed in a complicated manner. As the ELMs disappeared, energy confinement improved and remarkable changes in edge and scrape-off layer plasma properties were observed. These results demonstrate that active modification of plasma surface interactions can preempt large ELMs.
Date: May 14, 2009
Creator: Mansfield, D. K.; Kugel, H. W.; Maingi, R.; Bell, M. G.; Bell, R.; Kaita, R. et al.
Partner: UNT Libraries Government Documents Department

Lithium Surface Coatings for Improved Plasma Performance in NSTX

Description: NSTX high-power divertor plasma experiments have shown, for the first time, significant and frequent benefits from lithium coatings applied to plasma facing components. Lithium pellet injection on NSTX introduced lithium pellets with masses 1 to 5 mg via He discharges. Lithium coatings have also been applied with an oven that directed a collimated stream of lithium vapor toward the graphite tiles of the lower center stack and divertor. Lithium depositions from a few mg to 1 g have been applied between discharges. Benefits from the lithium coating were sometimes, but not always seen. These improvements sometimes included decreases plasma density, inductive flux consumption, and ELM frequency, and increases in electron temperature, ion temperature, energy confinement and periods of MHD quiescence. In addition, reductions in lower divertor D, C, and O luminosity were measured.
Date: February 19, 2008
Creator: Kugel, H W; Ahn, J -W; Allain, J P; Bell, R; Boedo, J; Bush, C et al.
Partner: UNT Libraries Government Documents Department

NSTX Plasma Response to Lithium Coated Divertor

Description: NSTX experiments have explored lithium evaporated on a graphite divertor and other plasma facing components in both L- and H- mode confinement regimes heated by high-power neutral beams. Improvements in plasma performance have followed these lithium depositions, including a reduction and eventual elimination of the HeGDC time between discharges, reduced edge neutral density, reduced plasma density, particularly in the edge and the SOL, increased pedestal electron and ion temperature, improved energy confinement and the suppression of ELMs in the H-mode. However, with improvements in confinement and suppression of ELMs, there was a significant secular increase in the effective ion charge Zeff and the radiated power in H-mode plasmas as a result of increases in the carbon and medium-Z metallic impurities. Lithium itself remained at a very low level in the plasma core, <0.1%. Initial results are reported from operation with a Liquid Lithium Divertor (LLD) recently installed.
Date: January 21, 2011
Creator: Kugel, H. W.; Bell, M. G.; Allain, J. P.; Bell, R. E.; Ding, S.; Gerhardt, S. P. et al.
Partner: UNT Libraries Government Documents Department

Status and Plans for the National Spherical Torus Experimental Research Facility

Description: An overview of the research capabilities and the future plans on the MA-class National Spherical Torus Experiment (NSTX) at Princeton is presented. NSTX research is exploring the scientific benefits of modifying the field line structure from that in more conventional aspect ratio devices, such as the tokamak. The relevant scientific issues pursued on NSTX include energy confinement, MHD stability at high beta, non-inductive sustainment, solenoid-free start-up, and power and particle handling. In support of the NSTX research goal, research tools are being developed by the NSTX team. In the context of the fusion energy development path being formulated in the US, an ST-based Component Test Facility (CTF) and, ultimately a high beta Demo device based on the ST, are being considered. For these, it is essential to develop high performance (high beta and high confinement), steady-state (non-inductively driven) ST operational scenarios and an efficient solenoid-free start-up concept. We will also briefly describe the Next-Step-ST (NSST) device being designed to address these issues in fusion-relevant plasma conditions.
Date: July 27, 2005
Creator: Columbia University
Partner: UNT Libraries Government Documents Department