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The Kinetic Stabilizer: Further Calculations and Options

Description: The Kinetic Stabilizer, employing injected and mirror-reflected ion beams, represents a method for stabilizing axisymmetric mirror and tandem mirror systems. Building on earlier work, this paper presents further calculations on the concept and explores some new options that promise to enhance its capabilities.
Date: June 19, 2002
Creator: Post, R.F.
Partner: UNT Libraries Government Documents Department

MHD-Stabilization of Axisymmetric Mirror Systems Using Pulsed ECRH

Description: This paper, part of a continuing study of means for the stabilization of MHD interchange modes in axisymmertric mirror-based plasma confinement systems, is aimed at a preliminary look at a technique that would employ a train of plasma pressure pulses produced by ECRH to accomplish the stabilization. The purpose of using sequentially pulsed ECRH rather than continuous-wave ECRH is to facilitate the localization of the heated-electron plasma pulses in regions of the magnetic field with a strong positive field-line curvature, e. g. in the 'expander' region of the mirror magnetic field, outside the outermost mirror, or in other regions of the field with positive field-line curvature. The technique proposed, of the class known as 'dynamic stabilization,' relies on the time-averaged effect of plasma pressure pulses generated in regions of positive field-line curvature to overcome the destabilizing effect of plasma pressure in regions of negative field-line curvature within the confinement region. As will also be discussed in the paper, the plasma pulses, when produced in regions of the confining having a negative gradient, create transient electric potentials of ambipolar origin, an effect that was studied in 1964 in The PLEIDE experiment in France. These electric fields preserve the localization of the hot-electron plasma pulses for a time determined by ion inertia. It is suggested that it may be possible to use this result of pulsed ECRH not only to help to stabilize the plasma but also to help plug mirror losses in a manner similar to that employed in the Tandem Mirror.
Date: November 20, 2009
Creator: Post, R F
Partner: UNT Libraries Government Documents Department

The kinetic tandem concept: theory and computer simulations of the potential barriers

Description: The Kinetic Tandem fusion plasma confinement concept is a member of the class of open magnetic confinement systems whose magnetic topology is that of a tube of magnetic flux open at both ends. In open-ended systems the central problem is that of limiting the rate of plasma losses out the ends. In a conventional tandem mirror system end-plugging is accomplished by the generation of positive potential barriers within special short mirror cells located at each end of a long central confinement cell. The kinetic tandem concept accomplishes the same end result by employing dynamic effects, but without the necessity of special end cells. The field employed in the kinetic tandem is a simple axially symmetric solenoidal field whose intensity tapers to low values at the ends. Since the field line curvature is everywhere positive such a field is stabilizing for MHD interchange modes. Into each end are injected ion beams that are aimed nearly parallel to the field line direction. The ions from these beams then are radially compressed, stopped, and reflected back by magnetic mirror action in climbing up the magnetic gradient. In this way ion density peaks are formed between which the plasma is to be confined. As in the original tandem mirror concept, a localized ambipolar potential arises to maintain quasi-neutrality between the ions and the electrons. provided the plasma density in the plugs is higher than that of the plasma contained between them the ions of the central plasma will be confined between the plugs by the positive potential barriers represented by the plugs. The plasma electrons will at the same time be confined by the overall positive potential of the plasma with respect to the ends. In this report some analytical calculations of the formation of the plugs will be given. These calculations were then ...
Date: February 11, 1999
Creator: Byers, J A & Post, R F
Partner: UNT Libraries Government Documents Department

Drift waves in rotating plasmas

Description: The stability of the electron drift wave is investigated in the presence of E x B plasma rotation typical of the central cell plasma in tandem mirrors. It is shown that a rotationally-driven drift wave may occur at low azimuthal mode numbers. Conditions for rotational instabilities are derived. Quasilinear formulas are given for the anomalous transport associated with the unstable fluctuations.
Date: September 1, 1983
Creator: Horton, W. & Liu, J.
Partner: UNT Libraries Government Documents Department

MINIMARS: an attractive small tandem mirror fusion reactor

Description: Through the innovative design of a novel end plug scheme employing octopole MHD stabilization, we present the conceptual design of ''MIMIMARS'', a small commercial fusion reactor based on the tandem mirror principle. The current baseline for MINIMARS has a net electric output of 600 MWe and we have configured the design for short construction times, factory-built modules, inherently safe blanket systems, and multiplexing in station sizes of approx. 600 to 2400 MWe. We demonstrate that the compact octopole end cell provides a number of advantages over the more conventional quadrupole (yin-yang) end cell encountered in the MARS tandem mirror reactor study, and enables ignition to be achieved with much shorter central cell lengths. Accordingly, being economic in small sizes, MINIMARS provides an attractive alternative to the more conventional larger conceptual fusion reactors encountered to date, and would contribute significantly to the lowering of utility financial risk in a developing fusion economy.
Date: November 13, 1985
Creator: Perkins, L.J.; Logan, B.G.; Doggett, J.N.; Devoto, R.S.; Nelson, W.D.; Lousteau, D.C. et al.
Partner: UNT Libraries Government Documents Department

Improved system for perpendicular electron-cyclotron emission measurements on TMX-Upgrade

Description: Perpendicular electron-cyclotron emission (PECE) is used on TMX-U to diagnose thermal-barrier hot electrons (T/sub H/ approx. 100 to 400 keV); yielding the time history of the temperature of these relativistic electrons. We describe an improved quasi-optical viewing system for these measurements that uses high sensitivity superheterodyne receivers at fixed frequencies of 60, 98, 130, and 196 GHz. The improved viewing and transport system consists of an off-axis ellipsoidal mirror that images the plasma onto a V-band conical collection horn, an overmoded circular waveguide (7/8'' diam) that transports the radiation outside the vacuum vessel where the polarization is selected, and a high absorptivity Macor beam dump to prevent internal wall reflections from entering the viewing system. A relativistic code is used to calculate optically thin PECE signals from relativistic electrons for various energy and pitch angle distributions. 4 refs., 4 figs.
Date: March 7, 1986
Creator: Lasnier, C.J.; Ellis, R.F. & James, R.A.
Partner: UNT Libraries Government Documents Department

Using perpendicular electron-cyclotron emission to diagnose the thermal barrier electrons in TMX-Upgrade. Progress report

Description: Possibilities are explored for diagnosing the hot-electron distribution function for the thermal barriers of tandem mirrors using perpendicular electron-cyclotron emission. Emission from a relativistic bimaxwellian with a loss cone is calculated in the single-particle limit. Formulae are derived for finding T/sub perpendicular/ for a bimaxwellian by measuring frequencies of the harmonic intensity maxima at optically thin frequencies, or the intensity at optically thick frequencies. A positive par. delta f/par. delta p/sub perpendicular/ in the distribution function is shown to lead to decreased absorption, and instability for low T/sub perpendicular/. Methods are discussed for diagnosing the loss-cone distribution by comparing numerical calculation with measured intensity ratios and frequencies at the harmonic peaks. Finally, the perpendicular source function in the single-particle limit for this distribution function is calculated.
Date: January 1, 1983
Creator: Celata, C.M.
Partner: UNT Libraries Government Documents Department

The ''Kinetic Stabilizer'': A Simpler Tandem Mirror Confinement?

Description: In the search for better approaches to magnetic fusion it is important to keep in mind the lessons learned in the 50 years that fusion plasma confinement has been studied. One of the lessons learned is that ''closed'' and ''open'' fusion devices differ fundamentally with respect to an important property of their confinement, as follows: Without known exception closed systems such as the tokamak, the stellarator, or the reversed-field pinch, have been found to have their confinement times limited by non-classical, i.e., turbulence-related, processes, leading to the requirement that such systems must be scaled-up in dimensions to sizes much larger than would be the case in the absence of turbulence. By contrast, from the earliest days of fusion research, it has been demonstrated that open magnetic systems of the mirror variety can achieve confinement times close to that associated with classical, i.e., collisional, processes. While these good results have been obtained in both axially symmetric fields and in non-axisymmetric fields, the clearest cases have been those in which the confining fields are solenoidal and axially symmetric. These observations, i.e., of confinement not enhanced by turbulence, can be traced theoretically to such factors as the absence of parallel currents in the plasma, and to the constraints on particle drifts imposed by the adiabatic invariants governing particle confinement in axisymmetric open systems. In the past the MHD instability of axially symmetric open systems has been seen as a barrier to their use. However, theory predicts MHD-stable confinement is achievable if sufficient plasma is present in the ''good curvature'' regions outside the mirrors. This theory has been confirmed by experiments on the Gas Dynamic Trap mirror-based experiment at Novosibirsk, In this paper a new way of exploiting this stabilizing principle, involving creating a localized ''stabilizer plasma'' outside a mirror, will be discussed. To ...
Date: June 15, 2000
Creator: Post, R.F.
Partner: UNT Libraries Government Documents Department

Technician support for operation and maintenance of large fusion experiments: the tandem mirror experiment upgrade (TMX-U) approach

Description: As experiments continue to grow in size and complexity, a few technicians will no longer be able to maintain and operate the complete experiment. Specialization is becoming the norm. Subsystems are becoming very large and complex, requiring a great deal of experience and training for technicians to become qualified maintenance/operation personnel. Formal in-house and off-site programs supplement on-the-job training to fulfill the qualification criteria. This paper presents the Tandem Mirror Experiment-Upgrade (TMX-U) approach to manpower staffing, some problems encountered, possible improvements, and safety considerations for the successful operation of a large experimental facility.
Date: December 1, 1983
Creator: Mattson, G.E.
Partner: UNT Libraries Government Documents Department

Transient plasma estimation: a noise cancelling/identification approach

Description: The application of a noise cancelling technique to extract energy storage information from sensors occurring during fusion reactor experiments on the Tandem Mirror Experiment-Upgrade (TMX-U) at the Lawrence Livermore National Laboratory (LLNL) is examined. We show how this technique can be used to decrease the uncertainty in the corresponding sensor measurements used for diagnostics in both real-time and post-experimental environments. We analyze the performance of algorithm on the sensor data and discuss the various tradeoffs. The algorithm suggested is designed using SIG, an interactive signal processing package developed at LLNL.
Date: March 1, 1985
Creator: Candy, J.V.; Casper, T. & Kane, R.
Partner: UNT Libraries Government Documents Department

Database tools for enhanced analysis of TMX-U data. Revision 1

Description: A commercial database software package has been used to create several databases and tools that assist and enhance the ability of experimental physicists to analyze data from the Tandem Mirror Experiment-Upgrade (TMX-U) experiment. This software runs on a DEC-20 computer in M-Division's User Service Center at Lawrence Livermore National Laboratory (LLNL), where data can be analyzed offline from the main TMX-U acquisition computers. When combined with interactive data analysis programs, these tools provide the capability to do batch-style processing or interactive data analysis on the computers in the USC or the supercomputers of the National Magnetic Fusion Energy Computer Center (NMFECC) in addition to the normal processing done by the TMX-U acquisition system. One database tool provides highly reduced data for searching and correlation analysis of several diagnostic signals within a single shot or over many shots. A second database tool provides retrieval and storage of unreduced data for use in detailed analysis of one or more diagnostic signals. We will show how these database tools form the core of an evolving offline data analysis environment on the USC computers.
Date: March 6, 1986
Creator: Stewart, M.E.; Carter, M.R.; Casper, T.A.; Meyer, W.H.; Perkins, D.E. & Whitney, D.M.
Partner: UNT Libraries Government Documents Department

Control of gas input and background pressure in the end plug regions of the TMX-U thermal barrier experiment

Description: Rate equations for the plasma species in a thermal barrier end plug establish an upper bound on the neutral pressure (P) external to the plasma. For the Tandem Mirror Experiment-Upgrade (TMX-U), this bound is P less than or equal to 0.5 - 1.0 x 10/sup -6/ Torr. Initially TMX-U did not satisfy this criterion, and axial end plugging of plasma losses seemed limited by the excessive pressure. Subsequently, we modified the machine to improve the vacuum conditions, decreasing P to the desired range. At the same time axial end plugging of plasma losses increased to the duration of neutral beam injection and ECRH heating. Here we summarize our experimental measurements of gas input.
Date: October 26, 1983
Creator: Turner, W.C.; Nexsen, W.E.; Allen, S.L.; Hooper, E.B.; Hunt, A.L.; Lang, D.D. et al.
Partner: UNT Libraries Government Documents Department

Cost study of the ESPRESSO blanket for a Tandem Mirror Reactor

Description: A detailed cost study of the ESPRESSO blanket concept for the Tandem Mirror Fusion Reactor (TMR) has been performed to complement the thermal-hydraulic parametric study and to help narrow down the choice of parameters for the final design. The ESPRESSO blanket consists of a number of structurally independent ring modules. Each ring module is made up of a number of mutually pressure-supporting canisters containing arrays of breeder tubes. Two separate helium coolant flows are used: a main flow to cool the tube bank and a cooler first wall flow.
Date: February 1, 1986
Creator: Raffray, A.R.; Hoffman, M.A. & Gaskins, T.
Partner: UNT Libraries Government Documents Department

Evolution of the mirror machine

Description: The history of the magnetic-mirror approach to a fusion reactor is primarily the history of our understanding and control of several crucial physics issues, coupled with progress in the technology of heating and confining a reacting plasma. The basic requirement of an MHD-stable plasma equilibrium was achieved following the early introduction of minimum-B multipolar magnetic fields. In refined form, the same magnetic-well principle carries over to our present experiments and to reactor designs. The higher frequency microinstabilities, arising from the non-Maxwellian particle distributions inherent in mirror machines, have gradually come under control as theoretical prescriptions for distribution functions have been applied in the experiments. Even with stability, the classical plasma leakage through the mirrors posed a serious question for reactor viability until the principle of electrostatic axial stoppering was applied in the tandem mirror configuration. Experiments to test this principle successfully demonstrated the substantial improvement in confinement predicted. Concurrent with advances in mirror plasma physics, development of both high-power neutral beam injectors and high-speed vacuum pumping techniques has played a crucial role in ongoing experiments. Together with superconducting magnets, cryogenic pumping, and high-power radiofrequency heating, these technologies have evolved to a level that extrapolates readily to meet the requirements of a tandem mirror fusion reactor.
Date: August 18, 1983
Creator: Damm, C. C.
Partner: UNT Libraries Government Documents Department

Failure analysis of Ti - 15% Ta getter wire used for sublimation in the vacuum chambers of the Tandem Mirror Experiment

Description: The Tandem Mirror Experiment uses Ti-15% Ta getter wire for sublimation in the vacuum chambers in which the magnets are located. These wires have failed prematurely in service, resulting in increased costs and downtime. We have used optical metallography to show that the reason for these failures was the cycling of the material through the alpha-beta transition temperature, causing alpha-titanium precipitation at the grain boundaries, depression of the melting temperatures of those boundaries, and the subsequent melting of those boundaries in areas where the wires had achieved localized higher temperatures.
Date: August 19, 1983
Creator: Kershaw, R.P.; Gross, R.J. & Dalder, E.N.C.
Partner: UNT Libraries Government Documents Department

ICRF heating of passing ions in a thermal barrier tandem mirror

Description: Ion heating is used in the central cells of tandem mirrors to reduce the collisional trapping of passing ions in the end cell thermal barriers. In this paper, we reevaluate ICRF heating of the TMX-U central cell in two limits. The first we term isotropic, because we impose the condition that ions heated in the perpendicular direction be confined for at least one 90/sup 0/ scattering time, thereby heating the passing ions. The second we call anisotropic heating. It uses higher ICRF power to mirror trap a majority of the ions near the midplane, thereby reducing the density and collisionality of passing ions. Anisotropic heating has the advantage of increasing with ICRF power, whereas isotropic heating is limited by ion collisionality. Both techniques require gas fueling near the central cell midplane, with an ion cyclotron resonance toward each end cell to heat the cold ions.
Date: May 1, 1985
Creator: Molvik, A.W.; Dimonte, G.; Campbell, R.; Barter, J.; Cummins, W.F.; Falabella, S. et al.
Partner: UNT Libraries Government Documents Department

Vacuum measurements on the Tandem Mirror Experiment Upgrade (TMX-U) fusion experiment

Description: The gas inventory of the Tandem Mirror Experiment Upgrade (TMX-U) must be carefully controlled, if it is to successfully create various plasma configurations for thermal-barrier experiments designed to provide an improved performance for tandem-mirror experiments. This paper is a progress report on the calibration methods and pressure measurements of machine conditions deriving from recently improved neutral-beam gas control, and changes to the internal baffling geometry and the gettering system.
Date: August 12, 1983
Creator: Calderon, M.O.; Hunt, A.L.; Lang, D.D.; Nexsen, W.E.; Pickles, W.L. & Turner, W.C.
Partner: UNT Libraries Government Documents Department

User's manual for the FLORA equilibrium and stability code

Description: This document provides a user's guide to the content and use of the two-dimensional axisymmetric equilibrium and stability code FLORA. FLORA addresses the low-frequency MHD stability of long-thin axisymmetric tandem mirror systems with finite pressure and finite-larmor-radius effects. FLORA solves an initial-value problem for interchange, rotational, and ballooning stability.
Date: April 1, 1985
Creator: Freis, R.P. & Cohen, B.I.
Partner: UNT Libraries Government Documents Department

Plasma measurements with the TMX-U E parallel to B end-loss-ion spectrometers

Description: Two E parallel to B end-loss-ion spectrometers (ELIS) are now making plasma measurements on Tandem Mirror Experiment-Upgrade (TMX-U). One instrument is mounted on each end of this open-ended tandem-mirror machine. These spectrometers observe plasma losses along magnetic-field lines. They operate reliably and with a minimum of attention during an experimental run. Their data, which are quickly acquired and analyzed, help guide the experimental sequence. The parallel electric and magnetic fields separate the end-loss ions according to mass (D/sup +/ and H/sup +/) and energy. Each spectrometer detects ions with an array of 128 flat collector plates that are made from copper-coated G10 epoxy fiberglass, normally used for printed-circuit boards. The ELIS diagnostic system produces a wealth of experimental information, including data on peak plasma potential, central-cell ion temperature, potentials in the thermal-barrier region, axial confinement and ion-end-loss plugging, energetic-electron losses, and hydrogen/deuterium concentrations. 6 refs., 5 figs.
Date: February 18, 1986
Creator: Foote, J.H.; Wood, B.E.; Brown, M.D. & Curnow, G.M.
Partner: UNT Libraries Government Documents Department

Plasma-wall interactions in tandem mirror machines

Description: A description is presented of the plasma-surface interactions in thermal-barrier tandem-mirror machines. The thermal-barrier mode of axial confinement is an integral part of a tandem mirror, and it dictates the required plasma conditions, particularly at the surface of the plasma. For this reason, a qualitative discussion of the thermal barrier is presented first in Section 2. A brief description of the experimental configuration used in tandem mirrors to create the thermal barrier is then examined in detail in Section 3; the TMX-U and MFTF-B machines are used as specific examples. In Section 4, the relevant plasma-surface interaction issues are addressed, and experimental results from currently operating tandom mirror machines are included. Section 5 is both a summary and a discussion of future work concerned with plasma-surface interactions in tandem mirrors.
Date: November 1, 1984
Creator: Allen, S.L.
Partner: UNT Libraries Government Documents Department

Titanium-getter testing for TMX-U

Description: This report summarizes the results of titanium-gettering tests performed during August and September of 1983. Several current and voltage schedules were evaluated for possible implementation with TMX-U's computer-controlled getter system. The tests were performed using 1/8-inch wire composed of 85% Ti and 15% Ta. Measurements of wire temperature as a function of getter current were made. We performed glow discharge cleaning (GDC) of the vessel with wires in place to determine if GDC had any adverse effect on wire lifetime.
Date: March 7, 1985
Creator: Clower, C.A. Jr.
Partner: UNT Libraries Government Documents Department

Maximum current densities from tandem high density systems

Description: The tandem high-density negative-ion-source system is optimized to identify the largest possible ion concentrations and extracted ion currents. The optimization includes varying the length of the second chamber, varying neutral gas and electron densities, and varying the ratio of atomic to molecular density. The electron excitation processes, e-V and E-V, are taken into account in the first chamber. Negative ions are formed through dissociative attachment in the second chamber.
Date: March 14, 1985
Creator: Hiskes, J.R.; Karo, A.M. & Willmann, P.A.
Partner: UNT Libraries Government Documents Department

Role of ECRH in potential formation for tandem mirrors

Description: The axial ion plugging potential in a tandem mirror is produced by electron cyclotron resonance heating (ECRH) applied at two locations in the end mirror cell. A second harmonic (..omega.. = 2..omega../sub c/) resonance is used near the midplane to generate hot electrons which yield an electron potential barrier between center cell electrons and electrons outboard of the end cell midplane. The latter group of electrons is then heated at the fundamental resonance (..omega.. = ..omega../sub c/) on the outboard side of the magnetic well which drives an ion confining potential. Fokker-Planck and Monte Carlo calculations show that such a configuration is achievable, and the scaling obeys a rather simple set of equations. Another aspect of this configuration is the experimental observation that the fundamental heating drives the overall potential of the device relative to the wall to approx. 1 kV. An analytic model predicts this behavior for very strong ECRH. Results are given a numerical study of electron confinement in a mirror cell owing to fundamental heating as the level of the rf electric field, E/sub rf/, is increased. For the second part of the paper, we show that moderate levels of uniformly distributed rf fields, called cavity fields, can result in very hot (>250 keV) tails in the electron distribution as seen in the TMX-U experiment.
Date: May 8, 1985
Creator: Rognlien, T.D.; Matsuda, Y. & Stewart, J.J.
Partner: UNT Libraries Government Documents Department