摘要:

Ray‐tracing studies have been combined with a simple wave power balance model to provide a complete, albeit approximate, description of microwave power deposition in the ELMO Bumpy Torus (EBT‐I), EBT‐Scale (EBT‐S), and EBT Proof‐of‐Principle (EBT‐P) devices. Electron cyclotron absorption of ordinary and extraordinary waves by the combined core plasma and relativistic annuli is calculated using a fully relativistic damping package developed for theraysgeometrical optics code. The rays are traced in finite‐beta bumpy cylinder plasma equilibria that are obtained from the Oak Ridge National Laboratory (ORNL) two‐dimensional (2D) equilibrium code. These results for direct, single‐pass absorption are combined with results from a statistical model for the deposition of multiple reflected and mode‐converted waves to obtain estimates of the power deposited in the core, surface, and annulus plasma components. Wave absorption by the annuli and by the core components at the fundamental and second harmonic resonances, reflection, and Budden tunneling of the extraordinary mode at the right‐hand cutoff, and conversion between ordinary and extraordinary modes upon wall reflection are the processes included in the power balance model. Experimental measurements of wave power flux on the cavity wall in EBT‐S made with a simple microwave calorimeter are in good agreement with predictions of the model for a variety of operating configurations.

ISSN:0031-9171    

DOI:10.1063/1.864686

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The reflection coefficientRfor linear monochromatic ion acoustic waves incident on the transonic layer and sheath from the plasma interior is calculated. The treatment differs from previous analyses in that (1) the exact zero‐order ion density and velocity profiles for a planar, bounded plasma are used, and the zero‐order charge separation is not neglected, and (2) the first‐order quantities near the transonic layer are considered in detail, including first‐order charge separation, whereby it is found that no coupling to the beam modes exists, and that the functional form of the first‐order solution is completely determined. It is shown that the upper bound for ‖R‖ is (1)/(3) . The largest reflection occurs for frequencies which are small compared with the ionization frequency, and generally decreases with increasing frequency. By Fourier superposition, the reflection of a pulse is computed. For a narrow incident pulse, the reflected pulse is greatly distorted and is small compared with the incident pulse. For a broad pulse, the reflected pulse is similar in shape to the incident pulse, and has a magnitude which is approximately (1)/(3) of the incident pulse.

ISSN:0031-9171    

DOI:10.1063/1.864687

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The linear, relativistic gyrokinetic equation is derived, in a form appropriate for relativistic electrons in fusion research. The frequency of the perturbing wave satisfies &ohgr;≪&OHgr;e. The use of generally covariant transformation rules, as well as first‐order Hamiltonian perturbation theory, greatly simplifies the derivation. New results are presented for relativistic guiding center motion.

ISSN:0031-9171    

DOI:10.1063/1.864688

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Analytical models are derived for stabilization of the Rayleigh–Taylor instability of an ablatively accelerated slab. The procedure is to conserve mass, momentum, and energy flux across a perturbed interface through which plasma flows. In various regimes, the stabilization mechanism can be described as vortex shedding, compressibility, thermal conduction, and ablation. Comparisons are made with recent fluid simulations, and simple laws relevant to laser‐driven ablative acceleration are derived.

ISSN:0031-9171    

DOI:10.1063/1.864689

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The kinematic behavior of a dilute, two‐dimensional ‘‘gas’’ of parallel twisted magnetic flux tubes in a highly conducting fluid is considered. Collisions between flux tubes with the same sense of twist are inelastic due to the reconnection of their oppositely directed azimuthal magnetic field components at impact. In some collisions, the tension in the reconnected magnetic flux is sufficient to bind the two flux tubes together. Collisions between flux tubes with the opposite sense of twist are elastic. It is shown that a tenuous gas of individual twisted flux tubes condenses into two large‐scale regions of magnetic field with opposite twists. This calculation illustrates the results of Montgomery and co‐workers on the migration of magnetic energy towards small wavenumbers in two‐dimensional magnetohydrodynamic (MHD) turbulence. In particular, this problem illustrates the dynamical nonequilibrium of the relaxation phase in turbulent MHD systems.

ISSN:0031-9171    

DOI:10.1063/1.864690

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The propagation of electrical streamers in gases has long been controversial. Not all of the controversial issues are fundamental, however, to streamer modeling. An analysis is presented which focuses on those issues that are fundamental such as the electron avalanche process, space‐charge field distortion, and the development of a filamentary structure. The model predicts that streamer propagation is determined by the electrostatic potential driving the streamer, by the preionization generated immediately ahead of the streamer, and by the avalanche characteristics of the gas. The scaling of propagation speed with these parameters is obtained through the use of similarity and related arguments. Support for the analysis comes from experiments utilizing lasers to preionize air and guide electrical streamers.

ISSN:0031-9171    

DOI:10.1063/1.864698

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Wave excitation and fast ion generation in a double plasma device are studied experimentally. Results show how a compressive density perturbation, propagating as a wave, is formed in the target plasma when a positive potential pulse is externally applied. Further, it is shown that fast ions are generated in a narrow plasma region close to the sheath near the grid because of reflection by the wave front during propagation of the wave.

ISSN:0031-9171    

DOI:10.1063/1.864699

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A high‐frequency hot electron instability is observed in ELMO Bumpy Torus (EBT) plasmas when the hot electron‐to‐ion density ratio exceeds 0.4. Both the real frequency and the imaginary frequency are larger than the ion cyclotron frequency. The azimuthal mode number (m) is 7, and the instability rotates in the hot electron curvature drift direction. This instability is identified as a curvature‐driven mode. When it is strongly excited, the equilibrium of the hot electron annuli and confined plasmas are destroyed (disruption). Ion heating and neutron bursts are associated with this instability.

ISSN:0031-9171    

DOI:10.1063/1.864700

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The electron density fluctuation spectrum in the range of frequencies below the ion plasma frequency (the ‘‘ion feature’’) is investigated in plasmas where the ion acoustic waves are weakly damped. The situation typical in laboratory plasmas where the electron temperature is larger than the ion temperature is considered in detail. Analytical expressions are given in the limit of weak damping and the variations of the spectrum with the relevant parameters are readily obtained, including the dependence on frequency, wavenumber, temperature ratio, drift velocity, and the concentrations of light impurity ions. Velocity distributions with non‐Maxwellian tails are also considered. An experiment is described in which the scattering of CO2laser radiation from a discharge plasma is studied. The observed fluctuation spectrum corresponds to the ion feature, in that the dependence of the observed frequencies on wavenumber corresponds to the dispersion relation of ion acoustic waves. They are only observed, however, in the edge plasma where drifting ions enhance the fluctuation level, and not in the plasma center, where light impurities in the argon plasma damp out the ion resonance.

ISSN:0031-9171    

DOI:10.1063/1.864701

出版商:AIP    

年代:1984

数据来源: AIP