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  • Institute of Physics  (26)
  • American Institute of Physics (AIP)  (10)
  • Copernicus  (3)
  • 1
    Electronic Resource
    Electronic Resource
    All-orders spectral calculation of radio-frequency heating in two-dimensional toroidal plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1573-1583 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectral calculations of radio-frequency (rf) heating in tokamak plasmas are extended to two dimensions (2-D) by taking advantage of new computational tools for distributed memory, parallel computers. The integral form of the wave equation is solved in 2-D without any assumption regarding the smallness of the ion Larmor radius (ρ) relative to the perpendicular wavelength (λ⊥). Results are therefore applicable to all orders in k⊥ρ, where k⊥=2π/λ⊥. Previous calculations of rf wave propagation and heating in 2-D magnetized plasmas have relied on finite Larmor radius expansions (k⊥ρ(very-much-less-than)1) and are thus limited to relatively long wavelengths. In this paper, no such assumption is made, and we consider short wavelength processes such as the excitation and absorption of ion Bernstein waves in 2-D with k⊥ρ〉1. Results show that this phenomenon is far more complex than simple one-dimensional plasma models would suggest. Other applications include fully self-consistent 2-D solutions for high-harmonic fast-wave heating in spherical tokamaks. These calculations require the storage and inversion of a very large, dense matrix, but numerical convergence can be improved by writing the plasma current in the laboratory frame of reference. To accurately represent the wave spectrum in this frame, the local plasma conductivity is corrected to first order in ρ/L, where L is the equilibrium scale length. This correction is necessary to ensure accuracy in calculating the wave spectrum and hence the fraction of power absorbed by ions and electrons. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1359516
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  • 2
    Electronic Resource
    Electronic Resource
    Advances in full-wave modeling of radio frequency heated, multidimensional plasmas : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1873-1881 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previous full-wave models for rf heating in multidimensional plasmas have relied on either cold-plasma or finite Larmor radius approximations. These models assume that the perpendicular wavelength of the rf field is much larger than the ion Larmor radius, and they are therefore limited to relatively long wavelengths and low cyclotron harmonics. Recently, alternate full-wave models have been developed that eliminate these restrictions. These "all orders spectral algorithms" take advantage of new computational techniques for massively parallel computers to solve the integral form of the wave equation in multiple dimensions without any restriction on wavelength relative to orbit size, and with no limit on the number of cyclotron harmonics retained. These new models give high-resolution, two-dimensional solutions for mode conversion and high harmonic fast wave heating in tokamak geometry. In addition, they have been extended to give fully three-dimensional solutions of the integral wave equation for minority ion cyclotron heating in stellarator geometry. By combining multiple periodic solutions for individual helical field periods, it is possible to obtain complete wave solutions valid over the entire volume of the stellarator for arbitrary antenna geometry. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455001
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of Alfvén resonance on low-frequency fast wave current drive (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2760-2764 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Alfvén resonances may occur on the low- and high-field sides for a low-frequency fast wave current drive scenario proposed for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion 31, 1135 (1991)]. At the resonance on the low-field side, the fast wave may be mode converted into a short-wavelength slow wave, which can be absorbed by electrons at the plasma edge, before the fast wave propagates into the core area of the plasma. Such absorption may cause a significant parasitic power loss. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871241
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  • 4
    Electronic Resource
    Electronic Resource
    A falling head permeameter for the measurement of the hydraulic conductivity of granular solids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3942-3946 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A falling head permeameter is described in which pairs of infrared emitters and detectors on a sight tube are used to measure the flow rate associated with the passage of water through a granular solid under the action of a diminishing pressure head. An equation relating pressure head to elapsed time is derived from which permeability may be calculated. In order to verify the accuracy and sensitivity of the instrument, permeability measurements carried out on a graded quartz sand are compared to those obtained by the more conventional constant head measurement. Excellent agreement is obtained between the permeability values obtained using both measurement methods. Experimental results are also reported for the measurement of the permeability of a range of sieved sand fractions. The falling head permeameter described here is particularly suitable for the measurement of the hydraulic conductivity of granular solids such as sands and soils through which a high flow rate may be expected. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310349
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  • 5
    Electronic Resource
    Electronic Resource
    A high pressure permeameter for the measurement of liquid conductivity of porous construction materials (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3397-3401 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Equipment is described which provides measurements of the pressure and volume of unidirectional liquid flow through sample cores of porous solids. The real-time measurement of flow pressures enables any changes in conductivity resulting either from interactions with the flow liquid or from changes in effective stress levels to be monitored directly. The equipment can use a range of flow liquids and be adapted for miscible and immiscible displacement studies. It is particularly suitable for cement-based and stone construction materials. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149926
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  • 6
    Electronic Resource
    Electronic Resource
    Database tools for enhanced analysis of TMX-U data (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1929-1931 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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-Divisions's User Service Center at Lawrence Livermore National Laboratory (LLNL), where data can be analyzed off line 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 off-line data analysis environment on the USC computers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138799
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  • 7
    Electronic Resource
    Electronic Resource
    Mode selection by priming in an overmoded electron cyclotron maser (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 212-227 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been found that an externally injected signal can strongly influence the steady-state electromagnetic mode in which a pulsed electron cyclotron maser (ECM) operates. A careful experimental examination reveals that the process by which this occurs is similar to the oscillator phase priming noted previously in magnetron work. It is found here that the degree of mode control depends on the injected signal power level (relative to the ECM noise power level), frequency, and time of application. Mode control is obtained at power levels nearly four orders of magnitude below that of the steady-state ECM output power and over frequency bandwidths several times that of the cavity resonance band. The optimum input signal is a circularly polarized wave, corotating with the electron cyclotron motion. The experimental results are compared with a quasilinear coupled-mode theory. The theory is used to provide analytic predictions of the temporal mode evolution through third-order coupling. The comparison with experiment indicates that higher-order terms are non-negligible in some regimes of operation. However, this model suitably predicts ECM steady-state operation over much of the operating parameter space and gives a qualitative understanding of the role of the external signal and preoscillation noise in the mode selection process. Mode priming may enable stable and efficient single-mode operation of the ECM and other overmoded sources of coherent radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859939
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  • 8
    Electronic Resource
    Electronic Resource
    Electromotive excitation of a plasma sheath (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1081-1091 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heating of the electrons in a plasma by radio frequency (rf) fields results in an electron distribution function that can be highly non-Maxwellian. The response of these heated electrons can lead to a substantially larger total potential drop than that obtained by arbitrarily choosing a single-temperature parameter to describe the electron distribution in a traditional Boltzmann approximation. Electromotively driven rf fields can have scale lengths along a static magnetic field line that are much larger than a Debye length and produce electron–sheath interactions that are best described as collisions. Estimates of the floating potential of a plasma that is excited by electromotively driven rf plasma currents parallel to a strong static magnetic field have been made using a Fermi acceleration heating model and linear estimates for the rf fields with plasma. When this non-Maxwellian distribution function is used for estimates of the static potential, the results show that the total potential drop is proportional to the rf oscillation energy and the square root of the ion to electron mass ratio. Numerical solutions to Poisson's equation are presented for non-Boltzmann electrons. Analytic estimates of parasitic rf power absorption and edge profile modification using a Bohm diffusion model are presented. Estimates for a purely electrostatic heating operator with rf fields that are assumed to scale as the Debye length along static magnetic field lines are also made for comparison with the electromagnetic result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860466
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  • 9
    Electronic Resource
    Electronic Resource
    Collective ion acceleration and relativistic electron-beam propagation (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 1632-1637 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results on the collective acceleration of ions using a relativistic electron beam (0.5 MeV, 30 kA, 60 ns) are presented. A gas cloud consisting of either H2, He, or N2 gas was used as the ion source. Ion species, charge state, and energy were measured. Ions were accelerated as derived from the hydrogen and helium gas sources but not from the nitrogen gas source. In almost all shots significant numbers of hydrogen and carbon impurity ions were accelerated. The electron beam exhibited asymmetric propagation characteristics in the region immediately downstream from the anode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334483
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  • 10
    Electronic Resource
    Electronic Resource
    Collisional effects on coherent nonlinear wave–particle interactions at cyclotron harmonics (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 100-109 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When particle orbits are trapped very near a cyclotron harmonic resonance, the quasilinear concept of weakly perturbed, uncorrelated passages through resonance breaks down, and nonlinear effects become important. In numerical as well as analytic studies, it is demonstrated that relativistic detuning of the resonance can be important for electrons even at low initial energies (∼20 eV) and that coupling to perturbed parallel motion can lead to strong interactions for values of the turning point where the wave frequency differs from a harmonic multiple of the bounce-averaged gyrofrequency by an integral multiple of the bounce frequency. The resultant motion is described by large periodic energy excursions for which small-angle Coulomb collisions or other randomization processes are required to realize net heating. Analytic formulas are derived describing the energy excursion behavior and heating in a mildly relativistic limit. Also, a Monte Carlo numerical model of the collisional effects on the orbits has been employed to study electron heating at the second-harmonic cyclotron resonance and to test the analytic results. In certain regimes of collisionality, a strong enhancement over quasilinear heating has been found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865985
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