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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-beta, low-aspect-ratio ("compact") stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2–4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A β=4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at β=4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 790-793 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The external inductance of an axisymmetric toroidal plasma with an arbitrary aspect ratio and cross section is obtained using a Green's function method. By varying an equivalent skin current density over the plasma surface, while keeping the total toroidal current fixed, the plasma boundary is made to coincide with a magnetic surface. Numerical computations of the self-inductance and mutual inductance as functions of aspect ratio and elongation are fitted to simple analytic formulas. The effect of distributed plasma current on the volt-seconds required to reach a prescribed net current is considered.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wave absorption in the ISX-B tokamak [Phys. Rev. Lett. 44, 647 (1980)] at the second harmonic (ω=2ωce) of the electron-cyclotron frequency is reported. Measurements of the absorption of a wave polarized in the extraordinary mode and propagating perpendicular to the toroidal magnetic field are in agreement with computations.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Runaway electron formation and confinement occur readily in pulsed torsatrons and heliotrons because of the high loop voltages during initiation and termination of the helical and vertical fields ("field ramping'') and the inherently good containment of the electrons on the flux surfaces in the vacuum fields. This has been confirmed for the Advanced Toroidal Facility (AFT) [Fusion Technol. 10, 179 (1986)] and other stellarators by orbit calculations. Since runaway electrons can cause an unacceptable level of hard x rays near the machine, a runaway electron suppression system was incorporated in ATF. The main component of the system is a movable paddle, which is normally left in the center of the plasma chamber during the field ramps. This device, in conjunction with programmed vertical field ramping, which reduces the volume of good flux surfaces, has proved to be very effective in reducing the runaway electron population. Measurements of hard x rays from ATF have shown that the runaway electrons are produced primarily during the field ramping but that there is usually also a small steady-state runaway electron component during the"flat-top'' portion of the fields. The paddle is the main source of the hard x radiation (thick-target bremsstrahlung). There is evidence that some of the runaway electrons may be confined to islands. The maximum x-ray energy found by pulse height analysis is ∼12–15 MeV. The mean energy appears to be a few million electron volts. There is a noticeable forward peaking of the bremsstrahlung from the paddle. The limiters do not appear to be major sources of x rays.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2870-2878 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The understanding of tokamak transport depends on the exploration of a wide range of theoretical models and of a variety of toroidal experiments. This report considers the contributions that nontokamak, but toroidal, experiments can make to our understanding of tokamak transport as well as theoretical alternatives to the standard drift wave model of tokamak transport.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2987-2987 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The diamagnetic diagnostic on ATF consists of two systems. The first uses a single-turn diamagnetic loop in a stainless-steel reentrant tube inside the vacuum vessel. Compensation signals are derived from Rogowski coils mounted on the main helical and vertical coil buses. This arrangement provides maximum sensitivity and the fastest time response, but results in signals which are dominated by noise created by the large ATF SCR power supplies. The nonlinear nature of these supplies, and their coupling, requires the use of hybrid noise reduction processing. The analog compensation loops remove the low-frequency components and digital post-processing removes the high-frequency ones. The second diamagnetic signal is derived from a set of saddle loops which respond directly to the Pfirsch-Schlüter current in the plasma. Typical results are presented. This research was sponsored by the Office of Fusion Energy, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The beam from an electron gun was used to trace flux surfaces in the Advanced Toroidal Facility (ATF) torsatron. The ATF magnetic field was run steady state at 0.1 T, and the electron beam was detected optically with an image-intensified, solid-state camera when it impinged on a phosphor-coated screen. Closed flux surfaces and islands at several low-order resonances were observed. The largest island, located at the ι= 1/2 surface, was from 5 to 6 cm in width, and its presence implied the existence of magnetic field errors. To determine if these error fields could be traced to small misalignments of the magnetic coils, a device capable of accurately measuring the radial and vertical magnetic field components of individual coil sets was placed in the center of ATF. This device allowed for a determination of the precise location of each of the coils that make up the ATF coil set. No significant coil misalignments were found. A further investigation of the coil configuration led to the identification of dipole fields in the helical field coil leads as the source of the field errors. The techniques developed in making these measurements are described in the text.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1572-9591
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Tokamak Physics Experiment is designed to develop the scientific basis for a compact and continuously operating tokamak fusion reactor. It is based on an emerging class of tokamak operating modes, characterized by beta limits well in excess of the Troyon limit, confinement scaling well in excess of H-mode, and bootstrap current fractions approaching unity. Such modes are attainable through the use of advanced, steady state plasma controls including strong shaping, current profile control, and active particle recycling control. Key design features of the TPX are superconducting toroidal and poloidal field coils; actively-cooled plasma-facing components; a flexible heating and current drive system; and a spacious divertor for flexibility. Substantial deuterium plasma operation is made possible with an in-vessel remote maintenance system, a lowactivation titanium vacuum vessel, and shielding of ex-vessel components. The facility will be constructed as a national project with substantial participation by U.S. industry. Operation will begin with first plasma in the year 2000.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 12 (1993), S. 215-219 
    ISSN: 1572-9591
    Keywords: Programmatic framework ; tokamak physics experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Significant advances have been made in the confinement of reactor-grade plasmas, so that we are now preparing for experiments at the “power breakeven” level in the JET and TFTR experiments. In ITER we will extend the performance of tokamaks into the burning plasma regime, develop the technology of fusion reactors, and produce over a gigawatt of fusion power. Besides taking these crucial steps toward the technical feasibility of fusion, we must also take steps to ensure its economic acceptability. The broad requirements for economically attractive tokamak reactors based on physics advancements have been set forth in a number of studies. An advanced physics data base is emerging from a physics program of concept improvement using existing tokamaks around the world. This concept improvements program is emerging as the primary focus of the U.S. domestic tokamak program, and a key element of that program is the proposed Tokamak Physics Experiment (TPX). With TPX we can develop the scientific data base for compact, continuously-operating fusion reactors, using advanced steady-state control techniques to improve plasma performance. We can develop operating techniques needed to ensure the success of ITER and provide first-time experience with several key fusion reactor technologies. This paper explains the relationships of TPX to the current U.S. fusion physics program, to the ITER program, and to the development of an attractive tokamak demonstration plant for this next stage in the fusion program.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 17 (1998), S. 189-191 
    ISSN: 1572-9591
    Keywords: Stellarators ; compact stellarators ; fusion reactors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Stellarators offer advantages for reactors, namely the potential for steady state operation with low recirculating power (high engineering Q) and without disruptions. A substantial portion of the world fusion program is devoted to the development of stellarators as a magnetic confinement system. The world stellarator program, as it currently exists, is focused on high-aspect-ratio (R/a = 5 − 11) designs that lead to very large reactors. For example the German advanced stellarator reactor design HSR has an aspect ratio of 12 and a major radius of 22 m. An important issue for stellarator research is whether more compact reactor designs are possible. Could the advantage of stellarators also be realized at dimensions and performance levels closer to those of the advanced tokamak reactor ARIES-RS (R = 5.5 m, neutron wall load of 4 MW/m2)? Theory has identified a class of “compact stellarator” plasma configurations that could be the basis for such a design. They are promising, but need to be studied experimentally in order to realistically assess their potential. The most cost-effective way to accomplish this is to carry out the compact stellarator proof-of-principle program that has been proposed by the U.S. stellarator community. This program would answer the basic physics questions for compact stellarators and make important contributions to the world stellarator knowledge base at a cost (about $30M/year) that is modest compared to expenditures for stellarator and tokamak research world-wide.
    Type of Medium: Electronic Resource
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