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  • 1
    Electronic Resource
    Electronic Resource
    Effect of edge biasing on electrostatic fluctuations and particle transport in a nonfusion magnetoplasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1459-1466 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper concerns experiments about the role of a radial electric field on the plasma turbulence in a toroidal magnetoplasma, and the possibility of anomalous transport reduction through the application of external biasing potentials to the plasma edge. The experiments show, for positive applied bias potential, a progressive reduction of radial anomalous particle flux, as well as electrostatic fluctuations. Some results on statistical and spectral properties of plasma and density fluctuations are reported. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873965
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  • 2
    Electronic Resource
    Electronic Resource
    Self-similarity, power-law scaling, and non-Gaussianity of turbulent fluctuation flux in a nonfusion magnetoplasma (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3369-3377 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The statistical characteristics of turbulent particle flux Γturb due to the correlated fluctuations of density and E(vector)×B(vector)-drift velocity in the simple magnetized torus Thorello [S. Alba, M. Fontanesi, A. Galassi, C. Riccardi, and E. Sindoni, Phys. Essays 6, 225 (1993)] are studied. The focus is on the shape and the low-order moments (absolute width, rms width, skewness, and kurtosis) of the probability distribution functions (PDF), and on how they change as a function of time-resolution τ upon coarse-graining. The way the shape of the PDF and its moments change are closely linked to each other, and they lend support to the view of two distinct regimes, separated by τbreak(approximate)50 μs. In both regimes, however, the statistical evidence for self-similarity, power-law scaling, and non-Gaussianity is rather mixed. The behavior at small τ is interpreted as due to the presence of smooth, positively correlated (and possibly coherent, i.e., long-lived) structures within the data, and the behavior at large τ as due to the standard (i.e., Gaussian, as opposed to the Levy–Gnedenko) Central Limit Theorem. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1493792
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental analysis of drift waves destabilization in a toroidal plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3749-3758 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper concerns the study of the development of turbulence in a toroidal magnetoplasma [C. Riccardi et al., Plasma Phys. 36, 1791 (1994)]. This analysis has been performed by evaluating wave number, frequency spectra, and bicoherence coefficients of density fluctuations associated to drift wave propagation. Plasma parameters have been changed over a wide range, in order to identify and characterize density fluctuations both in absence and in presence of nonlinear phenomena. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872499
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of plasma loading in the presence of electrostatic waves (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3588-3594 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental analysis of the plasma impedance with respect to the coupling of ES (electrostatic) waves is described in this paper. The waves are excited through a slow-wave antenna and the experiment performed in a toroidal device [C. Riccardi et al., Plasma Phys. 36, 1791 (1994)]. The measured impedance is compared with a simple theoretical model for magnetized homogeneous plasma, in order to establish the presence of bulk or surface waves and of some nonlinear effects when power is raised. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871058
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental study and simulations of electronegative discharges at low pressure (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3735-3742 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed an experimental and theoretical analysis of the rf discharges at low pressure in a small reactor for industrial applications. In particular, we focused on the plasma produced from electronegative gases (air and SF6) in the low pressure range between 0.05 and 1 mbar. The device pumping system sustains a flow velocity of about 50 cm/s, with residence time in the discharge of about 0.2 s, at P=0.1 mbar. The discharge parameters have been measured by means of movable electrostatic probes and lies in the range ne≅107–109 cm−3, ni≅1010–1012 cm−3, and Te≅5–10 eV. Particular care in the analysis of the data proved necessary due to the presence of a substantial amount of negative ions. On the other hand, we have performed simulations of the discharge composition through the implementation of a suitable numerical model of the chemical kinetics in the device. On the basis of the experiments, a comparison of charged species production with those predicted by the theory was performed and a more realistic description of the involved phenomena was obtained. In particular, several assumptions concerning the ion diffusion coefficient were tested, allowing one to pin down the relative importance of transport and bulk processes in the discharge state. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1392967
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  • 6
    Electronic Resource
    Electronic Resource
    Radio frequency phase shifters for launching waves in a magnetized plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2888-2891 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A variable phase-shifting system, able to generate phase-shifted replicas of the same reference input signal, has been designed to properly feed the antenna system within a plasma device. The system is based on a phase-locked loop used as a voltage controlled phase shifter and is able to provide four phase-shifted output signals. The phase differences between adjacent outputs can be varied between 0° and 100°, and are maintained equal to each other, with a precision of less than 3° in the range 2.5–10 MHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145573
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison between fast-sweep Langmuir probe and triple probe for fluctuations measurements : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 461-464 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two techniques are applied and the results compared both in the plasma core and in the edge region of "Thorello," to estimate electron temperature fluctuations. The first method is a fast-sweep Langmuir probe: it is a new apparatus based on a dual channel circuit that compensates for stray capacitance and permits sweep speeds up to 400 kHz, so that we can investigate the electrostatic turbulence with good temporal resolution. The second technique is the conventional triple probe: this method allows us to measure density, temperature, and floating potential as a function of time. The fast-sweep Langmuir probe provides a more reliable electron temperature fluctuations and these measurements are essential for a correct interpretation of density and potential fluctuations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310578
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  • 8
    Electronic Resource
    Electronic Resource
    A 400 kHz, fast-sweep Langmuir probe for measuring plasma fluctuations (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2681-2688 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel, fast-sweep Langmuir probe has been constructed and successfully operated on "Thorello." It is based on a novel, dual channel circuit that compensates for stray capacitance and permits sweep speeds up to 400 kHz. The circuit response has been tested by measuring the known current–voltage characteristics of resistors and diodes. In addition, the probe has been used to measure the electron temperature and density as well as the plasma potential of plasmas generated in Thorello. A method of three-parameter curve fitting is used to analyze the time-dependent data. The measurements compare favorably with those derived from other standard probe techniques. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149828
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  • 9
    Electronic Resource
    Electronic Resource
    A study on the modification of density and plasma potential in presence of electron temperature fluctuations (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 465-465 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Electron temperature fluctuations have been investigated in the plasma of "Thorello," a small toroidal device (minor radius a=8 cm and major radius R=40 cm) which produces a magnetized plasma in steady-state condition without rotational transform (n≅1011 cm−3; Te≅2 eV; B=1000 G).1 In our experiment two techniques are applied to estimate T˜e: triple Langmuir probe technique and fast-sweep Langmuir probe method, in both cases, varying the density of the neutral source (in our plasma, H2). The so-called triple probe is the conventional method used to investigate T˜e, while fast-sweep Langmuir probe is a new diagnostic technique recently developed on Thorello.2 Our measurements have been performed in the frequency range between 0 and 500 kHz. The turbulent plasma exhibits a spectrum quite broad in frequency: power spectra of floating potential and density show the characteristic frequencies are in the range 0–100 kHz, while power spectra of electron temperature can extend up to 150–200 kHz. In the plasma core relative levels of electron temperature fluctuations are about 20%, but in the edge region these relative levels raise up to 50%. In situations where electron temperature fluctuations are not negligible, the measurement of T˜e is essential for obtaining a correct interpretation of density and potential fluctuations. In our case the level of electron temperature fluctuations is not negligible in the edge region and it was possible to separate I˜Si and ñ according to the hypothesis I˜Si/ISi=ñ/n+〈fraction SHAPE="CASE"〉12T˜e/Te and to the theory of thermal drift wave turbulence. Then we can particularly compare the mean values of Te, the level of temperature fluctuations measured in the same plasma, the power spectrum, and the correlation between temperature, density, and potential fluctuations applying the digital correlation technique.3 © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323473
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  • 10
    Electronic Resource
    Electronic Resource
    Wave-dynamical analysis of conversion and absorption of oblique extraordinary and Bernstein modes near the second electron-cyclotron harmonic (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1396-1404 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation and absorption of oblique second-harmonic electron-cyclotron waves in a plasma slab are studied by means of propagation equations directly deduced from the Vlasov–Maxwell system. An electromagnetic wave injected from the vacuum into the plasma can be transformed into a quasielectrostatic forward mode, which, in turn, is converted into a Bernstein backward wave. The occurrence of this double conversion process and the global absorption and reflection are analyzed, and the dependence of these phenomena on the plasma parameters and on the wave characteristics is investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858970
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