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  • 1
    Electronic Resource
    Electronic Resource
    Results from helical axis stellarators : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2238-2244 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Helical axis stellarators produce magnetic surfaces of high rotational transform and moderate shear solely by means of external currents, with the promise of high β. Several machines with quite different toroidal, helical, and "bumpy" Fourier components of magnetic field are now producing results, including high quality magnetic surfaces, confinement mode transitions, configuration studies, and confinement consistent with International Stellarator Scaling (ISS95) scaling up to Te∼2 keV. These devices permit concept evaluation over an unprecedented configuration space, and allow basic comparisons with those designed by established and alternative optimization strategies. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1364671
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  • 2
    Electronic Resource
    Electronic Resource
    Thresholds and the role of the radial electric field in confinement bifurcations in the H-1 heliac (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2390-2398 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The threshold conditions for the confinement bifurcations in the H-1 heliac [S. M. Hamberger et al., Fusion Technol. 17, 123 (1990)] are studied experimentally. The thresholds include the magnetic field, the rf power, and the neutral gas filling pressure. It is shown that in any combination of these parameters it is the radial electric field Er that is driven to a critical value before the bifurcation. A mechanism of the electric field formation is suggested, which is based on the balance of the electron and ion losses. The ion loss, at low magnetic field and high ion temperature observed in H-1, is dominated by the direct orbit loss mechanism. This is shown by modeling of the exact ion orbits and by comparing a qualitative picture of the Er formation with the experimental data. Relative efficiency of the electron and ion heating in the inner regions of plasma define the conditions for either low-to-high (L–H) or high-to low (H–L) confinement bifurcations in H-1. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872914
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  • 3
    Electronic Resource
    Electronic Resource
    Production of fast electrons in a prototype heliac by helicon waves (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 875-880 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The generation of plasma by helicon waves has been investigated in the Small Heliac Experimental Apparatus [Nucl. Fusion 25, 1485 (1985)]. Evidence for wave–particle interaction in both argon and helium is presented in the form of observations of the electron distribution function. A high energy bump-on-tail feature is shown to coincide with the wave phase velocity and with an energy corresponding to a large ionization cross section. It is shown that the bump-on-tail feature may be related to the ionization capability of helicon waves and may be a result of some form of radio frequency current drive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870746
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  • 4
    Electronic Resource
    Electronic Resource
    Observation of the neoclassical current in the Small Heliac Experimental Apparatus (SHEILA) (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3986-3991 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first measurements of internal currents in a toroidal heliac are reported. It is suggested that the toroidal current observed in the Small Heliac Experimental Apparatus (SHEILA) [Nucl. Fusion 25, 1485 (1985)] in the low density regime consists mainly of the bootstrap current and the Pfirsch–Schlüter current, the net toroidal component corresponding to the uni-directional bootstrap current, and the asymmetric radial profile of the observed current indicating a mixture of bootstrap current with the bi-directional Pfirsch–Schlüter current. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872518
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  • 5
    Electronic Resource
    Electronic Resource
    Helicon wave excitation and propagation in a toroidal heliac: Experiment and theory (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 803-810 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper a comparison between theoretical calculations and experimental measurements of helicon wave coupling by a partial-turn shielded antenna in a toroidal heliac is presented. Despite the complicated heliac geometry, the wave dispersion, field profiles, and antenna radiation resistance are described well by a cylindrical uniform plasma theory. It also presents a simple formula relating the radiation resistance to the measured wave magnetic field per unit antenna current. Finally, the scaling of these results to the Heliac-1 (H-1) [Fusion Technol. 17, 123 (1990)]; a larger heliac now operating at the Australian National University (ANU), is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871432
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic field mapping system on the H-1 heliac (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 467-467 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The H-1 heliac recently brought into operation is a medium-sized 3-field-period heliac with major radius R0=1 m, plasma mean minor radius 〈a〉≤0.2 m and a wide range of rotational transforms 0.6≤(large-closed-square)(0)≤2.0. Electron beam mapping of the vacuum magnetic field was performed using new type of a fluorescent target (movable fluorescent rod array having a transparency about 98%). Up to 150–200 of toroidal transits were observed at each electron gun position. The spatial resolution of the system was about 3 mm. Electron collector probes were used for monitoring the positions of the magnetic surfaces in different toroidal field periods. Visible paths of the electron beam due to the excitation of the background gas (p×10−4 Torr) were used for identification of the toroidal transit numbers. This newly developed method gives an accuracy in measurement of the rotational transform of about 1.5%. Experimental surfaces and measured (large-closed-square) profiles show very good agreement with the computer model results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146385
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  • 7
    Electronic Resource
    Electronic Resource
    A simple miniature magnetic probe with inherent electrostatic rejection (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3334-3335 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A modification of a basic center-tapped magnetic probe design has been developed wherein subtraction of capacitive signals is carried out by the probe itself. The electrostatic rejection of this probe is compared with other typical designs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144302
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic field mapping using an image-intensifying fluorescent probe (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1149-1156 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple, cost-effective image-intensifying fluorescent probe designed for mapping the magnetic surfaces in the heliac sheila is described. It consists of a phosphor-coated metal plate which is enclosed in a grounded U-channel that provides electrostatic shielding. An adjustable accelerating voltage is applied to the metal plate to greatly increase the cathodoluminescence produced by the directed electron beam from an electron gun, and the visible electron-beam image is recorded by a CCD camera. The gain in the image brightness allows significant reduction of the electron-beam energy to minimize the deviation of the measured drift surfaces from the true magnetic surfaces, and to improve resolution for detailed studies of surfaces in the newer stellarator experiments. This technique is particularly suited to electron energies below the phosphor activation threshold, when external image intensifying systems are likely to be very inefficient. Up to 36 toroidal rotations have been observed, limited mainly by the effective cross sections of the fluorescent probe and the electron gun. Mapping at low magnetic field strengths allows detection of small fixed amplitude field errors. Measurements of the gain characteristics and resolution are presented, with an example of the electrically variable resolution achievable with this design. The effect of electron energy on drift surfaces of a heliac is demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141993
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  • 9
    Electronic Resource
    Electronic Resource
    Digital interface for quadrature demodulation of interferometer signals (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 522-522 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a digital interface for processing signals produced by a scanning multichannel far-infrared interferometer/polarimeter for plasma density measurements. The interface samples the interferometer signals in quadrature before digital filtering, demodulation and downloading to a transputer array for real-time tomographic inversion and display. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146485
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  • 10
    Electronic Resource
    Electronic Resource
    Tomographic wire-grid imaging of magnetic surfaces : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4725-4727 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a new, fast, and accurate method for obtaining magnetic surface puncture plots by the use of a rotating grid of fine wires. Electrons launched from a small gun follow the magnetic field lines, and a fraction are intercepted by the wire grid. The current signals, chordal integrals of electron beam intensity, are inverted by an iterative pseudotomographic method to obtain an image of the electron beam density in the plane of the grid, that is, a puncture plot of the magnetic surface. The method is capable of high resolution while maintaining a high transparency to electrons, and is demonstrated on a small toroidal stellarator, the SHEILA heliac.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143620
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