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  • 1
    Electronic Resource
    Electronic Resource
    Self-consistent stochastic electron heating in radio frequency discharges (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4375-4383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fermi acceleration is considered as an underlying mechanism for electron heating in rf discharges, in which the heating arises from the reflection of electrons from moving sheaths. By examining the dynamics of the electron collisions with the sheaths, the map that describes the electron motion is derived. For high-frequency discharges (ω/2π〉50 MHz), the electron motion is shown to be stochastic. By combining these dynamics with collisional effects in the bulk plasma and incorporating self-consistent physical constraints, a self-consistent model of the discharge is developed. The model is used to calculate physically interesting quantities, such as the electron temperature and average lifetime, and to predict the minimum pressure necessary to sustain the plasma. The distribution of electron energies is shown to be non-Maxwellian. These results can be applied to experimentally interesting parallel-plate rf plasma discharges to predict the operating conditions necessary for stochastic heating to occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341286
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  • 2
    Electronic Resource
    Electronic Resource
    Self-consistent electron cyclotron resonance absorption in a plasma with varying parameters (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3924-3933 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A formalism is developed for numerically calculating reflection and absorption of right-hand polarized waves and reflection of left-hand polarized waves propagating into a cyclotron resonance zone in a medium in which both magnetic field and plasma density are varying. The results are shown to agree with previous analytic calculations in the limit of constant density, weak collisionality, and linearly varying magnetic field, where the analytic calculation applies. The formalism is then applied to a plasma with general field and density variations, and arbitrary collisionality. The absorption and reflections are calculated for various boundary conditions along the propagation path, showing that there is an optimum density for power absorption. The collisionless absorption in the resonance zone, calculated from the single particle heating averaged over the flux is shown to be consistent with the linear wave absorption at low absorption and collisionality. At high absorption a prescription for bringing the two calculation methods into agreement is advanced. The results are used to qualitatively explain some previously puzzling experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352244
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: "Modeling electronegative plasma discharges'' [J. Appl. Phys. 75, 2339 (1994)] (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 625-625 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358544
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  • 4
    Electronic Resource
    Electronic Resource
    Modeling electronegative plasma discharges (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2339-2347 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A macroscopic analytic model for a three-component electronegative plasma has been developed. Assuming the negative ions to be in Boltzmann equilibrium, a positive ion ambipolar diffusion equation is found. The electron density is nearly uniform, allowing a parabolic approximation to the plasma profile to be employed. The resulting equilibrium equations are solved analytically and matched to an electropositive edge plasma. The solutions are compared to a simulation of a parallel-plane rf driven oxygen plasma for two cases: (1) p=50 mTorr, ne0=2.4×1015 m−3, and (2) 10 mTorr, ne0=1.0×1016 m−3. In the simulation, for the low power case (1), the ratio of negative ion to electron density was found to be α0≈8, while in the higher power case α0≈1.3. Using an electron energy distribution that approximates the simulation distribution by a two-temperature Maxwellian, the analytic values of α0 are found to be close to, but somewhat larger than, the simulation values. The average electron temperature found self-cosistently in the model is close to that in the simulation. The results indicate the need for determining a two-temperature electron distribution self-consistently within the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356252
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  • 5
    Electronic Resource
    Electronic Resource
    Cavity perturbation measurement of plasma density in complex geometry rf discharges (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1618-1621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A noninvasive microwave diagnostic is used to determine the plasma density in a complex geometry rf discharge chamber. Data have been obtained using several cavity modes and a wide range of pressures and powers. The measured peak densities are approximately a factor of 2 lower than those obtained from Langmuir probe measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344375
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  • 6
    Electronic Resource
    Electronic Resource
    Time scale to ergodicity in the Fermi–Pasta–Ulam system (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 5 (1995), S. 283-297 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the approach to near-equipartition in the N-dimensional Fermi–Pasta–Ulam Hamiltonian with quartic (hard spring) nonlinearity. We investigate numerically the time evolution of orbits with initial energy in some few low-frequency linear modes. Our results indicate a transition where, above a critical energy which is independent of N, one can reach equipartition if one waits for a time proportional to N2. Below this critical energy the time to equipartition is exponentially long. We develop a theory to determine the time evolution and the excitation of the nonlinear modes based on a resonant normal form treatment of the resonances among the oscillators. Our theory predicts the critical energy for equipartition, the time scale to equipartition, and the form of the nonlinear modes below equipartition, in qualitative agreement with the numerical results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166143
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of a potential barrier created by electron cyclotron resonance heating (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 123-128 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electrostatic potential well and mirror-trapped hot electrons are created by high power (250 kW), short pulse (3 μsec) electron cyclotron resonance heating (ECRH) of a plasma in one magnetic mirror cell of a multiple mirror experiment. The creation and subsequent decay of the potential well is measured by an electron beam, time-of-flight diagnostic. Typically, the barrier rises to −40 V just after ECRH and decays within 100 μsec. A numerical model of the barrier evolution is developed, and the numerical results along with the experimental observations are presented. Both the numerical results and the experimental observations indicate a correlation between the degree of heating (diamagnetic loop voltage output) and the longevity of the barrier. It is shown that the decay of the barrier is determined mainly by the hot-electron escape rate and the hot-electron-neutral ionization rate, rather than by trapping of the passing ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866560
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  • 8
    Electronic Resource
    Electronic Resource
    Resistive effects on the rigid mode ballooning instability (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1416-1428 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: From a set of fluid equations, a second-order differential equation, governing the resistive ballooning instability for a mirror confined plasma with a rigid perturbation, is obtained. The resistive effects on the rigid mode ballooning instability are numerically examined for three tandem mirror configurations; those stabilized by walls, by end cusps, and by end quadrupoles. In the model the pressure is taken to be isotropic and constant along the axis except in the cusps and the diverging field regions, and the plasma has a sharp boundary. The theoretical results indicate that the resistivity can play a major role in determining the growth rate for ballooning for lower temperature devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866255
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  • 9
    Electronic Resource
    Electronic Resource
    Velocity diffusion in two-frequency electron cyclotron resonance heating (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 1061-1075 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-frequency electron cyclotron resonance heating (ECRH) is modeled by a four-dimensional mapping derived from the nonrelativistic single particle equations of motion. The model includes changes in parallel energy due to the spatially separate resonance zones. The intrinsic diffusion in parallel energy leads to axial losses in a magnetic trap which can rival those induced by collisions. An analytical model for this process gives a loss rate in good agreement with a numerical simulation. The quasilinear diffusion rate into the loss cone and the rate of Arnold diffusion through the adiabatic barrier are calculated for practical ECRH experiments, and compared with similar effects arising from interparticle collisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865904
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  • 10
    Electronic Resource
    Electronic Resource
    Hot-electron instability in mirror geometry (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3511-3514 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasmas with variable ratios of hot electrons to colder background plasma, but without significant neutral gas, are investigated in the multiple mirror experiment (MMX) [Phys. Fluids 29, 1208 (1986)]. The device permits, sequentially, the injection of plasma (H2 or He) into a stable mirror cell, and electron-cyclotron resonance heating (ECRH) to an electron temperature of several keV. A second source then provides the cold-electron component with arbitrary nc/nh≤50. At any point in time, the field coils that provide magnetohydrodynamic (MHD) stability for the hot electrons may be pulsed off for times short in comparison to the time required for cold plasma density to change. Instantaneous destabilization, even for plasma parameters well in excess of the value of nc/nh for which a hot-electron drift approximation would predict stability, was observed. This result suggests that a mechanism in addition to a cold plasma background is required to stabilize a hot-electron distribution. Comparison is made with recent theoretical work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865827
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