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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

Three-dimensional simulation of rotary latch assembly in seismic response and interactions

Description: The finite element method has been used to investigate the stress field in mechanical suspension systems. The critical seismic loads are depended on three-dimensional dynamic response of vacuum vessels and interactions of the equipment supporting structures to the vacuum vessels and supporting system. In this study of the optics assembly equipment (15 to 27 Hz), it was shown that the pressure vessel systems which supports the optics assembly systems (6.5 to 13 Hz) have significant influence in the seismic response of the rotary latch assembly. A potentially critical failure location is identified. An axisymmetrical elastic analysis predicts stress at the inner radius of the lower housing can be reduced by 60% with simple design modification. Use of three-dimensional dynamic model and static model to evaluate the combined complex stress permits prediction of the rotary latch assembly operating life and seismic safety.
Date: March 2, 1998
Creator: Leung, K.K.
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

Eddy current and quench loads and stress of SSC collider 4-K liner and the bore tube during magnet quench

Description: This paper describes the response of the eddy current and quench loads on a proposed Superconducting SuperCollider 4-K liner system. The liner within a bore tube is designed to remove the radiated power and the photodesorbed gas that impair the beam tube vacuum. The bimetallic liner tube is subjected to cooldown and eddy current loads. The square liner tube is a two-shell laminated Nitronic-40 steel is used for strength and a copper inner layer for low impedance to the image currents. Perforated holes are used to remove the photodesorbed gases for vacuum maintenance. The holes are located in a low-stress area of the liner. Rectangular holes in a four-pole symmetry pattern are required for beam dynamic stability. The liner is conductivity cooled by the round steel bore tube with a 2-mm wall. The copper layer must not be stressed over the yield strength limit because copper properties such as conductivity are known to change when the copper is stressed over yield strength. This analysis will address liner system response under thermal, eddy current, and vaporized liquid helium loads in a quenching dipole magnet.
Date: July 1, 1993
Creator: Leung, K.K. & Shu, Q.S.
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

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

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

Beam emittance measurements on multicusp ion sources

Description: Multicusp ion sources are used for various applications. Presently, the implementation of this type of ion source planned for the development of an ion beam lithography machine, which will be used for the projection of sub-0.2 {mu}m patterns onto a wafer substrate. Since, for this application, a very good beam quality and a small ion energy spread are required, emittance measurements have been performed on a multicusp ion source for various source conditions. It is shown that the installation of proper capacitors between the extraction electrodes is necessary to avoid rf-pickup, which otherwise leads to a distortion of the beam emittance. The influence of the magnetic filter field on the beam emittance has been investigated, and the beam emittance of a dc filament-discharge plasma has also been compared to that of an rf-generated plasma.
Date: August 1, 1995
Creator: Sarstedt, M.; Lee, Y. & Leung, K.N.
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

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

Performance Improvements of a Tritiated Water Recovery System

Description: Tritium processing equipment is installed inside gloveboxes. Leaks of tritium, normal and accidental, are captured by a tritium stripping system using an oxidation-absorption process. Tritium is captured as tritiated water in zeolite beds and is recovered by desorption and reduction. The regenerated zeolite beds are reused. Reduction of the tritiated water is accomplished by a zeolite bed recovery system using hot magnesium beds. The system has been in operation for about 10 years and met original design requirements. Recent expansion of the facility requires a higher capacity of the system. Operation data are collected and analyzed. Ways to increase the system capacity are discussed.
Date: August 16, 2004
Creator: Heung, Leung K.; Hsu, R. H.; Rice, J. L. & McGee, T. S.
Partner: UNT Libraries Government Documents Department

Geothermal Energy Databook for the Western United States (Draft Copy)

Description: The National Geothermal Information Resource (GRID) project of the Lawrence Berkley Laboratory was initiated in 1974 with the objective of compiling both basic and site-specific data on major aspects of geothermal energy utilization. During the past ten years much progress has been made in the United States to develop geothermal energy and to construct power plants. Current electrical power produced is 608 MWe at The Geysers in California which obtains steam to drive turbines from steam wells. However, the major new sources of geothermal energy in the next decade are expected to be hot brine systems located in the Western United States. Data on the power potential and progress toward utilization is needed for these new areas to identify impediments to utilization and to forecast power on-line in the next decades. However, the data is widely scattered and largely unevaluated, thereby impeding the analysis for predictions of power production in the decades 1980, 1990, and beyond the year 2000. The objective of this work is to provide a single, comprehensive database containing evaluated reference data useful in assessing geothermal sites for their potential to produce electrical power. The compilation and evaluation constitute a databook of current information for plant construction, modeling, research and development for conversion of geothermal energy to electric power production. The result of this work include identification of areas where data are lacking or are inadequate and where technology development is needed. The interest in site-specific data stems from two important concerns: (1) forecasts of power production related to local, state, and national goals, for example, the second report on geothermal energy by the Interagency Geothermal Coordinating Council which contains forecasts for power on-line to the year 2000 and beyond, and (2) the assessment of each site to produce power in an economic manner for a 20 ...
Date: June 1, 1979
Creator: Phillips, S. L.; Tavana, M.; Leung, K. & Schwartz, S. R.
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

Charge Accumulation at a Threading Edge Dislocation in GaN

Description: We have performed Monte Carlo calculations to determine the charge accumulation on threading edge dislocations in GaN as a function of the dislocation density and background dopant density. Four possible core structures have been examined, each of which produces defect levels in the gap and may therefore act as electron or hole traps. Our results indicate that charge accumulation, and the resulting electrostatic interactions, can change the relative stabilities of the different core structures. Structures having Ga and N vacancies at the dislocation core are predicted to be stable under nitrogen-rich and gallium-rich growth conditions, respectively. Due to dopant depletion at high dislocation density and the multitude of charge states, the line charge exhibits complex crossover behavior as the dopant and dislocation densities vary.
Date: January 20, 1999
Creator: Leung, K.; Stechel, E.B. & Wright, A.F.
Partner: UNT Libraries Government Documents Department

A D-D/D-T fusion reaction based neutron generator system for liver tumor BNCT

Description: Boron-neutron capture therapy (BNCT) is an experimental radiation treatment modality used for highly malignant tumor treatments. Prior to irradiation with low energetic neutrons, a 10B compound is located selectively in the tumor cells. The effect of the treatment is based on the high LET radiation released in the {sup 10}B(n,{alpha}){sup 7}Li reaction with thermal neutrons. BNCT has been used experimentally for brain tumor and melanoma treatments. Lately applications of other severe tumor type treatments have been introduced. Results have shown that liver tumors can also be treated by BNCT. At Lawrence Berkeley National Laboratory, various compact neutron generators based on D-D or D-T fusion reactions are being developed. The earlier theoretical studies of the D-D or D-T fusion reaction based neutron generators have shown that the optimal moderator and reflector configuration for brain tumor BNCT can be created. In this work, the applicability of 2.5 MeV neutrons for liver tumor BNCT application was studied. The optimal neutron energy for external liver treatments is not known. Neutron beams of different energies (1eV < E < 100 keV) were simulated and the dose distribution in the liver was calculated with the MCNP simulation code. In order to obtain the optimal neutron energy spectrum with the D-D neutrons, various moderator designs were performed using MCNP simulations. In this article the neutron spectrum and the optimized beam shaping assembly for liver tumor treatments is presented.
Date: April 2, 2003
Creator: Koivunoro, H.; Lou, T.P.; Leung, K. N. & Reijonen, J.
Partner: UNT Libraries Government Documents Department

High flux compact neutron generators

Description: Compact high flux neutron generators are developed at the Lawrence Berkeley National Laboratory. The neutron production is based on D-D or D-T reaction. The deuterium or tritium ions are produced from plasma using either a 2 MHz or 13.56 MHz radio frequency (RF) discharge. RF-discharge yields high fraction of atomic species in the beam which enables higher neutron output. In the first tube design, the ion beam is formed using a multiple hole accelerator column. The beam is accelerated to energy of 80 keV by means of a three-electrode extraction system. The ion beam then impinges on a titanium target where either the 2.4 MeV D-D or 14 MeV D-T neutrons are generated. The MCNP computation code has predicted a neutron flux of {approximately}10{sup 11} n/s for the D-D reaction at beam intensity of 1.5 A at 150 kV. The neutron flux measurements of this tube design will be presented. Recently new compact high flux tubes are being developed which can be used for various applications. These tubes also utilize RF-discharge for plasma generation. The design of these tubes and the first measurements will be discussed in this presentation.
Date: June 15, 2001
Creator: Reijonen, J.; Lou, T.-P.; Tolmachoff, B.; Leung, K.-N.; Verbeke, J. & Vujic, J.
Partner: UNT Libraries Government Documents Department