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Comments on velocity space relaxation in high charge-state plasma neutralizers

Description: Scaling of velocity space relaxation rates, which affect the final temperature of a natural beam, with ion charge state in plasma neutralizers is examined. Overall, this scaling indicates a substantial enhancement in emittance growth of the neutral beam with increase in the charge state of ions in plasma neutralizers. 9 refs.
Date: January 1, 1989
Creator: Hershcovitch, A.
Partner: UNT Libraries Government Documents Department

Reduction of residual charge in surface-neutralization-based neutral beams

Description: Hyperthermal-neutral beams have been proposed as a charge-free alternative to plasmas in select processing steps. Existing prototype sources include three generic types: gas-dynamic, ion-neutral-charge-exchange and ion-surface-neutralization beam sources. The authors find that in surface-neutralization type sources, which have the highest flux, residual current can still flow to the substrate. However, this charged particle flux is several orders of magnitude smaller than the hyperthermal-neutral flux. Here they discuss the source of this residual current and methods for further reductions. This is important to the semiconductor industry.
Date: April 1, 1997
Creator: Goeckner, M.J.; Bennett, T.K.; Park, J.; Wang, Z. & Cohen, S.A.
Partner: UNT Libraries Government Documents Department

Advances in the operation of the DIII-D neutral beam computer systems

Description: The DIII-D neutral beam system routinely provides up to 20 MW of deuterium neutral beam heating in support of experiments on the DIII-D tokamak, and is a critical part of the DIII-D physics experimental program. The four computer systems previously used to control neutral beam operation and data acquisition were designed and implemented in the late 1970`s and used on DIII and DIII-D from 1981--1996. By comparison to modern standards, they had become expensive to maintain, slow and cumbersome, making it difficult to implement improvements. Most critical of all, they were not networked computers. During the 1997 experimental campaign, these systems were replaced with new Unix compliant hardware and, for the most part, commercially available software. This paper describes operational experience with the new neutral beam computer systems, and new advances made possible by using features not previously available. These include retention and access to historical data, an asynchronously fired ``rules`` base, and a relatively straightforward programming interface. Methods and principles for extending the availability of data beyond the scope of the operator consoles will be discussed.
Date: February 1, 1998
Creator: Phillips, J.C.; Busath, J.L.; Penaflor, B.G.; Piglowski, D.; Kellman, D.H.; Chiu, H.K. et al.
Partner: UNT Libraries Government Documents Department

Final safety analysis report for the Ground Test Accelerator (GTA), Phase 2

Description: This document is the third volume of a 3 volume safety analysis report on the Ground Test Accelerator (GTA). The GTA program at the Los Alamos National Laboratory (LANL) is the major element of the national Neutral Particle Beam (NPB) program, which is supported by the Strategic Defense Initiative Office (SDIO). A principal goal of the national NPB program is to assess the feasibility of using hydrogen and deuterium neutral particle beams outside the Earth`s atmosphere. The main effort of the NPB program at Los Alamos concentrates on developing the GTA. The GTA is classified as a low-hazard facility, except for the cryogenic-cooling system, which is classified as a moderate-hazard facility. This volume consists of appendices C through U of the report
Date: October 1, 1994
Partner: UNT Libraries Government Documents Department

An orthotropic source of thermal atoms

Description: A highly efficient source that produces a narrow beam of neutral atoms at thermal velocity with small angular divergence is described. It uses a high work function interior surface to evaporate alkali atoms as ions and a low work function neutralizer, biased to collect the ions and evaporated them as neutral atoms. The neutralizer is located opposite an exit aperture so that the beam characteristics are determined by the geometry of the neutralizer and aperture. The orthotropic source is especially well suited for atomic clocks and for efficient loading of short lived radioactive alkali atoms into an optical trap.
Date: June 1, 1995
Creator: Dinneen, T.; Ghiorso, A. & Gould, H.
Partner: UNT Libraries Government Documents Department

Adaptive control technique for accelerators using digital signal processing

Description: The use of present Digital Signal Processing (DSP) techniques can drastically reduce the residual rf amplitude and phase error in an accelerating rf cavity. Accelerator beam loading contributes greatly to this residual error, and the low-level rf field control loops cannot completely absorb the fast transient of the error. A feedforward technique using DSP is required to maintain the very stringent rf field amplitude and phase specifications. 7 refs.
Date: January 1, 1987
Creator: Eaton, L.; Jachim, S. & Natter, E.
Partner: UNT Libraries Government Documents Department

Value engineering and the role of R and D in the neutral beam program

Description: Value Engineering, simply defined, is a systematic approach to getting more for your money. It has been used to reduce the cost of a wide variety of products by the D.O.D. and in principle, should be applicable to various phases of the Neutral Beam Program. With respect to R and D, the principles of Value Engineering must be used with caution. They are most effective in evaluating directed development with very specific goals, but can be misleading when considering advanced innovative work.
Date: May 14, 1979
Creator: Fink, J.
Partner: UNT Libraries Government Documents Department

Final safety analysis report for the Ground Test Accelerator (GTA), Phase 2

Description: This document is the second volume of a 3 volume safety analysis report on the Ground Test Accelerator (GTA). The GTA program at the Los Alamos National Laboratory (LANL) is the major element of the national Neutral Particle Beam (NPB) program, which is supported by the Strategic Defense Initiative Office (SDIO). A principal goal of the national NPB program is to assess the feasibility of using hydrogen and deuterium neutral particle beams outside the Earth`s atmosphere. The main effort of the NPB program at Los Alamos concentrates on developing the GTA. The GTA is classified as a low-hazard facility, except for the cryogenic-cooling system, which is classified as a moderate-hazard facility. This volume consists of failure modes and effects analysis; accident analysis; operational safety requirements; quality assurance program; ES&H management program; environmental, safety, and health systems critical to safety; summary of waste-management program; environmental monitoring program; facility expansion, decontamination, and decommissioning; summary of emergency response plan; summary plan for employee training; summary plan for operating procedures; glossary; and appendices A and B.
Date: October 1, 1994
Partner: UNT Libraries Government Documents Department

Final safety analysis report for the Ground Test Accelerator (GTA), Phase 2

Description: This document is the first volume of a 3 volume safety analysis report on the Ground Test Accelerator (GTA). The GTA program at the Los Alamos National Laboratory (LANL) is the major element of the national Neutral Particle Beam (NPB) program, which is supported by the Strategic Defense Initiative Office (SDIO). A principal goal of the national NPB program is to assess the feasibility of using hydrogen and deuterium neutral particle beams outside the Earth`s atmosphere. The main effort of the NPB program at Los Alamos concentrates on developing the GTA. The GTA is classified as a low-hazard facility, except for the cryogenic-cooling system, which is classified as a moderate-hazard facility. This volume consists of an introduction, summary/conclusion, site description and assessment, description of facility, and description of operation.
Date: October 1994
Partner: UNT Libraries Government Documents Department

Arc Snubbers Neutral Beam Sources

Description: At LBL it has been observed and verified many times that the amount of 1/2 CV{sup 2} energy associated with the accel grid that a neutral beam source can tolerate under sparkdown conditions is quite limited. If this energy exceeds approximately 5-7 Joules, serious degradation of the voltage holding capability of the source occurs. To allow a margin of safety, a 3 Joule maximum has been set as a design goal. It is perhaps relevant to note here that this limitation does not occur in the case of high vacuum modulator tubes where 50 Joules is acceptable and even beneficial. The difference is apparently associated with the few microns of gas present in neutral beam sources. This provides a much faster space charge neutralization capability in the accel gap so that a high current discharge can develop in a few nanoseconds. In a vacuum tube where the neutralizing ions must come from the electrodes, the time is much longer. A study of the latter type of breakdown was made for a switch-tube project at LLL, where this was found to be 1-2 {micro}secs. In a source, the discharge can be much more localized because of the gas and, in fact, may become a 'pinch' type discharge where the magnetic field of the arc column focuses the discharge into a small channel.
Date: January 1, 1979
Creator: Baker, W. R.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT TESTING OF THE U.S. COMMON LONG PULSE SOURCE AT 120KV

Description: The U.S. magnetic fusion energy program has developed a single design long pulse neutral beam source for TFTR, MFTF-B, and DIII-D. The arc is a very compact axial magnetic line cusp. The accelerator is an actively cooled tetrode with water cooled grid tubes of shaped molybdenum forming 'slot' beamlets. DIII-D and MFTF-B configurations have an 80 kV accelerator gap, with 12 x 48 cm aperture, and a 10 meter 'module' focus. TFTR modules are unfocused, with a 120 kV gap and 12 x 43 cm mask. The first CLPS was tested in the TFTR configuration, at 120 kV, 2 seconds. Optimum current was 73 Amperes, or 1.76 ppervs (deuterium), with 80% - 85% atomic fraction. Optimum divergence of ions plus neutrals was 0.4' parallel to the slots, and 0.7' perpendicular to the slots ( l / e half angle). The combination of an axial cusp magnetic bucket and slot accelerator apertures gives the CLPS about twice the beam power per unit cross section of other long pulse sources, plus lower divergence in the direction parallel to the slots.
Date: December 1, 1987
Creator: Vella, M. C.; Cooper, W. S. & Pincosy, P. A.
Partner: UNT Libraries Government Documents Department

Doppler-shifted neutral beam line shape and beam transmission

Description: Analysis of Doppler-shifted Balmer-{alpha} line emission from the TFTR neutral beam injection systems has revealed that the line shape is well approximated by the sum of two Gaussians, or, alternatively, by a Lorentzian. For the sum of two Gaussians, the broad portion of the distribution contains 40% of the beam power and has a divergence five times that of the narrow part. Assuming a narrow 1/e- divergence of 1.3{degrees} (based on fits to the beam shape on the calorimeter), the broad part has a divergence of 6.9{degrees}. The entire line shape is also well approximated by a Lorentzian with a half-maximum divergence of 0.9{degrees}. Up to now, fusion neutral beam modelers have assumed a single Gaussian velocity distribution, at the extraction plane, in each direction perpendicular to beam propagation. This predicts a beam transmission efficiency from the ion source to the calorimeter of 97%. Waterflow calorimetry data, however, yield a transmission efficiency of {approximately}75%, a value in rough agreement with predictions of the Gaussian or Lorentzian models presented here. The broad wing of the two Gaussian distribution also accurately predicts the loss in the neutralizer. An average angle of incidence for beam loss at the exit of the neutralizer is 2.2{degrees}, rather than the 4.95{degrees} subtended by the center of the ion source. This average angle of incidence, which is used in computing power densities on collimators, is shown to be a function of beam divergence.
Date: April 1, 1994
Creator: Kamperschroer, J. H.; Grisham, L. R.; Kokatnur, N.; Lagin, L. J.; Newman, R. A.; O`Connor, T. E. et al.
Partner: UNT Libraries Government Documents Department

Progress toward a microsecond duration, repetitive, intense-ion beam for active spectroscopic measurements on ITER

Description: The authors describe the design of an intense, pulsed, repetitive, neutral beam based on magnetically insulated diode technology for injection into ITER for spectroscopic measurements of thermalizing alpha particle and thermal helium density profiles, ion temperature, plasma rotation, and low Z impurity concentrations in the confinement region. The beam is being developed to enhance low signal-to-noise ratios expected with conventional steady-state ion beams because of severe beam attenuation and intense bremstrahlung emission. A 5 GW (e.g., 100 keV, 50 kA) one-microsecond-duration beam would increase the signal by 10{sup 3} compared to a conventional 5 MW beam with signal-to-noise ratios comparable to those from a chopped conventional beam in one second.
Date: June 1, 1996
Creator: Davis, H.A.; Bartsch, R.R. & Barnes, C.W.
Partner: UNT Libraries Government Documents Department

Five second helium neutral beam injection using argon-frost cryopumping techniques

Description: High power helium neutral beams for the heating of tokamak discharges can now be provided for 5 s by using argon cryopumping (of the helium gas) in the beamlines. A system has now been installed to deposit a layer of argon frost on the DIII-D neutral beam cryopanels, between tokamak injection pulses. The layer serves to trap helium on the cryopanels providing sufficient pumping speed for 5 s helium beam extraction. The argon frosting hardware is now present on two of four DIII-D neutral beamlines, allowing injection of up to 6 MW of helium neutral beams per discharge, with pulse lengths of up to 5 s. The argon frosting system is described, along with experimental results demonstrating its effectiveness as a method of economically extending the capabilities of cryogenic pumping panels to allow multi-second helium neutral beam injection.
Date: October 1, 1995
Creator: Phillips, J.C.; Kellman, D.H.; Hong, R.; Kim, J. & Laughon, G.M.
Partner: UNT Libraries Government Documents Department

Measurement of neutral beam profiles at DIII-D

Description: The neutral beam systems of DIII-D, a National Fusion Facility at General Atomics, are used both for heating the plasma, and as tools for plasma diagnostics. The spatial distribution (profile) and energy of the beam is used in the absolute calibration of both the Charge Exchange Recombination (CER) and Motional Stark Effect (MSE) diagnostics. In the past, the beam spatial profile used in these calibrations was derived from beam divergence calculations and IR camera observations on the tokamak centerpost target tiles. Two experimental methods are now available to better determine the beam profile. In one method, the Doppler shifted D{sub {alpha}} light from the energetic neutrals are measured, and the full-width at half-maximum (FWHM) of the beam can be inferred from the measured divergence of the D{sub {alpha}} light intensity. The other method for determining the beam profile uses the temperature gradients measured by the thermocouples mounted on the calorimeter. A new iterative fitting routine for the measured thermocouple data has been developed to fit theoretical models on the dispersion of the beam. The results of both methods are compared, and used to provide a new experimental verification of the beam profile.
Date: June 1, 1998
Creator: Chiu, H.
Partner: UNT Libraries Government Documents Department

Recent improvements to the DIII-D neutral beam instrumentation and control system

Description: The DIII-D neutral beam (NB) instrumentation and control (I and C) system provides for operational control and synchronization of the eight DIII-D neutral beam injection systems, as well as for pertinent data acquisition and safety interlocking. Recently, improvements were made to the I and C system. With the replacement of the NB control computers, new signal interfacing was required to accommodate the elimination of physical operator panels, in favor of graphical user interface control pages on computer terminal screens. The program in the mode control (MC) programmable logic controller (PLC), which serves as a logic-processing interface between the NB control computers and system hardware, was modified to improve the availability of NB heating of DIII-D plasmas in the event that one or more individual beam systems suddenly become unavailable while preparing for a tokamak experimental shot sequences. An upgraded computer platform was adopted for the NB control system operator interface and new graphical user interface pages were developed to more efficiently display system status data. A failure mode of the armor tile infrared thermometers (pyrometers), which serve to terminate beam pulsing if beam shine-through overheats wall thermal shielding inside the DIII-D tokamak, was characterized such that impending failures can be detected and repairs effected to mitigate beam system down-time. The hardware that controls gas flow to the beamline neutralizer cells was upgraded to reduce susceptibility to electromagnetic interference (EMI), and interlocking was provided to terminate beam pulsing in the event of insufficient neutralizer gas flow. Motivation, implementation, and results of these improvements are presented.
Date: November 1, 1997
Creator: Kellman, D.H. & Hong, R.
Partner: UNT Libraries Government Documents Department

Energetic neutral beam cleaning. Final CRADA report for CRADA number Y-1296-0427

Description: The purpose of this project is to evaluate the feasibility of cleaning silicon wafers with an energetic (1 to 100 eV) neutral particle beam and to develop a viable neutral beam source. A microwave plasma source on an existing test stand was modified to produce a 2-cm diameter neutral beam for cleaning the wafers. Significant results regarding neutral beam wafer cleaning are reported.
Date: December 31, 1996
Creator: Schechter, D.E.; Tsai, C.C. & Boitnott, C.
Partner: UNT Libraries Government Documents Department

Extending DIII-D Neutral Beam Modulated Operations with a Camac Based Total on Time Interlock

Description: A new total-on-time interlock has increased the operational time limits of the Neutral Beam systems at DIII-D. The interlock, called the Neutral Beam On-Time-Limiter (NBOTL), is a custom built CAMAC module utilizing a Xilinx 9572 Complex Programmable Logic Device (CPLD) as its primary circuit. The Neutral Beam Injection Systems are the primary source of auxiliary heating for DIII-D plasma discharges and contain eight sources capable of delivering 20MW of power. The delivered power is typically limited to 3.5 s per source to protect beam-line components, while a DIII-D plasma discharge usually exceeds 5 s. Implemented as a hardware interlock within the neutral beam power supplies, the NBOTL limits the beam injection time. With a continuing emphasis on modulated beam injections, the NBOTL guards against command faults and allows the beam injection to be safely spread over a longer plasma discharge time. The NBOTL design is an example of incorporating modern circuit design techniques (CPLD) within an established format (CAMAC). The CPLD is the heart of the NBOTL and contains 90% of the circuitry, including a loadable, 1 MHz, 28 bit, BCD count down timer, buffers, and CAMAC communication circuitry. This paper discusses the circuit design and implementation. Of particular interest is the melding of flexible modern programmable logic devices with the CAMAC format.
Date: November 1, 1999
Creator: Baggest, D.S.; Broesch, J.D. & Phillips, J.C.
Partner: UNT Libraries Government Documents Department

Automated Calculation of DIII-D Neutral Beam Availability

Description: The neutral beam systems for the DIII-D tokamak are an extremely reliable source of auxiliary plasma heating, capable of supplying up to 20 MW of injected power, from eight separate beam sources into each tokamak discharge. The high availability of these systems for tokamak operations is sustained by careful monitoring of performance and following up on failures. One of the metrics for this performance is the requested injected power profile as compared to the power profile delivered for a particular pulse. Calculating this was a relatively straightforward task, however innovations such as the ability to modulate the beams and more recently the ability to substitute an idle beam for one which has failed during a plasma discharge, have made the task very complex. For example, with this latest advance it is possible for one or more beams to have failed, yet the delivered power profile may appear perfect. Availability used to be manually calculated. This paper presents the methods and algorithms used to produce a system which performs the calculations based on information concerning the neutral beam and plasma current waveforms, along with post-discharge information from the Plasma Control System, which has the ability to issue commands for beams in real time. Plots representing both the requested and actual power profiles, along with statistics, are automatically displayed and updated each shot, on a web-based interface viewable both at DIII-D and by our remote collaborators using no-cost software.
Date: November 1, 1999
Creator: Phillips, J.C.; Hong, R.M. & Scoville, B.G.
Partner: UNT Libraries Government Documents Department

Schemes and Optimization of Gas Flowing into the Ion Source and the Neutralizer of the DIII-D Neutral Beam Systems

Description: Performance comparisons of a DIII-D neutral beam ion source operated with two different schemes of supplying neutral gas to the arc chamber were performed. Superior performance was achieved when gas was puffed into both the arc chamber and the neutralizer with the gas flows optimized as compared to supplying gas through the neutralizer alone. To form a neutral beam, ions extracted from the arc chamber and accelerated are passed through a neutralizing cell of gas. Neutral gas is commonly puffed into the neutralizing cell to supplement the residual neutral gas from the arc chamber to obtain maximum neutralization efficiency. However, maximizing neutralization efficiency does not necessarily provide the maximum available neutral beam power, since high levels of neutral gas can increase beam loss through collisions and cause larger beam divergence. Excessive gas diffused from the neutralizer into the accelerator region also increases the number of energetic particles (ions and secondary electrons from the accelerator grid surfaces) deposited on the accelerator grids, increasing the possibility of overheating. We have operated an ion source with a constant optimal gas flow directly into the arc chamber while gas flow into the neutralizer was varied. Neutral beam power available for injecting into plasmas was obtained based on the measured data of beam energy, beam current, beam transmission, beam divergence, and neutralization efficiency for various neutralizer gas flow rates. We will present the results of performance comparison with the two gas puffing schemes, and show steps of obtaining the maximum available beam power and determining the optimum neutralizer gas flow rate.
Date: November 1, 1999
Creator: Hong, R.M. & Chiu, H.K.
Partner: UNT Libraries Government Documents Department

Discharge characteristics of a plasma generator for SITEX (Surface Ionization with Transverse Extraction) and VITEX (Volume Ionization with Transverse Extraction) ion sources

Description: Surface Ionization with Transverse Extraction (SITEX) and Volume Ionization with Transverse Extraction (VITEX) ion sources are being developed to produce intense beams of light negative ions for neutral particle beam applications. The salient feature of these ion sources is their ability to form intense negative-ion beams. With the objective of improving the performance of these sources, an experimental study of their plasma properties has been conducted. The effects of various electrodes in the plasma generator were investigated. Low electron and ion temperatures (below 1 eV) and positive plasma potential up to +6 V have been measured. The measured distributions of plasma density and potential reveal the existence of multichamber characteristics in the source plasma. The significant discharge characteristics and the plasma properties associated with the performance of SITEX and VITEX ion sources are discussed.
Date: January 1, 1986
Creator: Tsai, C.C.; Dagenhart, W.K.; Stirling, W.L.; Barber, G.C.; Haselton, H.H.; Ryan, P.M. et al.
Partner: UNT Libraries Government Documents Department

Conceptual design for the ZEPHYR neutral-beam injection system

Description: In June 1980, the Lawrence Berkeley Laboratory began a conceptual design study for a neutral beam injection system for the ZEPHYR ignition tokamak proposed by the Max-Planck-Institut fur Plasmaphysik in Garching, Germany. The ZEPHYR project was cancelled, and the LBL design effort concluded prematurely in January 1981. This report describes the conceptual design as it existed at that time, and gives brief consideration to a schedule, but does not deal with costs.
Date: March 1, 1981
Creator: Cooper, W. S.; Elischer, V. P.; Goldberg, D. A.; Hopkins, D. B.; Jacobson, V. L.; Lou, K. H. et al.
Partner: UNT Libraries Government Documents Department

Extracted current densities from surface conversion sources of negative ions

Description: The condition for extracting a maximum negative ion current density is found when the product of the radius of the negative ion conversion electrode, the cross-section for negative and positive ion recombination, and the density of positive ions in the ion source equals one. The optimum output is obtained at the highest positive ion density and the smallest electrode radius.
Date: February 10, 1982
Creator: Fink, J.H.
Partner: UNT Libraries Government Documents Department

Very-high-level neutral-beam control system

Description: As increasing numbers of neutral beams are added to fusion machines, their operation can consume a significant fraction of a facility's total resources. LBL has developed a very high level control system that allows a neutral beam injector to be treated as a black box with just 2 controls: one to set the beam power and one to set the pulse duration. This 2 knob view allows simple operation and provides a natural base for implementing even higher level controls such as automatic source conditioning.
Date: October 1, 1981
Creator: Elischer, V.; Jacobson, V. & Theil, E.
Partner: UNT Libraries Government Documents Department