770 Matching Results

Search Results

Advanced search parameters have been applied.
in subjects: "Plasma Waves"  
prev Results: 601 - 624 next
open access

Excitation of drift waves by lower hybrid waves

Description: The excitation of low frequency oscillations by lower hybrid waves at electric fields lower than the thresholds of other parametric decay processes is reported. The frequencies and wavelengths of these oscillations agree with the collisional drift wave dispersion relation. The excitation is localized deep inside the plasma density gradient. The excited drift waves change the density profile and the lower hybrid wave trajectory.
Date: March 1, 1977
Creator: Wong, K. L. & Bellan, P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Trapped particles and harmonic generation

Description: A novel fluid-particle algorithm has been used to study the evolution of continuously generated ion acoustic waves numerically. The code permits the simultaneous analysis of the two nonlinearities involved: wave steepening or harmonic generation, a fluid effect; and wave damping and amplitude oscillations, a particle effect. For a temperature ratio 10 < T/sub e//T/sub i/ < 30, the behavior of low amplitude long wavelength waves is well described by a Korteweg-deVries equation augmented to inclu… more
Date: unknown
Creator: Hobbs, W. E. Jr. & DeGroot, J. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

[Experimental and theoretical plasma physics program]. Technical progress [in FY 1981]

Description: In recent years, members of the Maryland Theory Group have made significant contributions to the national fusion theory programs and in many cases these theoretical development helped to interpret experimental results and to design new experimental programs. In the following, the authors summarize the technical progress in five major areas: (1) rf interaction with plasmas including wave propagation, rf heating, rf induced runaways and current drive; (2) spheromak -- formation, equilibrium, and … more
Date: December 31, 1981
Creator: Griem, H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Integral eigenmode analysis of shear flow effects on the ion temperature gradient mode

Description: Previous numerical and analytic kinetic studies have investigated the influence of velocity shear on the ion temperature gradient (ITG) mode. These studies relied on a differential approximation to study mode structures with k[sub [perpendicular]][rho][sub i] [much lt] 1. A recently developed gyrokinetic integral code is here used to explore the effects of sheared flows on the ITG mode for arbitrary values of k[sub [perpendicular]][rho][sub i]. It is found that both the mode structure and eigen… more
Date: July 1, 1993
Creator: Artun, M.; Reynders, J. V. M. & Tang, W. M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Numerical study of the system of differential equations for the drift wave in tokamaks

Description: The following report discusses the authors' numerical study of a form of the drift wave equations which makes use of the usual quadratic approximation for the ion Z-function term and the usual exponential approximation for the electron Z-function term. Our recent work has shown that the electron Z-function term is not well represented by the exponential. Nevertheless, the numerical methods discussed in this report are similar to those which are applicable in the general case using the Z-functio… more
Date: March 1, 1978
Creator: Smith, J. & Whitson, J.C.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Study of Coupling Between Neutral-Air Motion and the Ionosphere

Description: The coupling between (1) an acoustic wave originating at or below the earth's surface and (2) the ionosphere is described by equations of continuity and motion. The plasma concentration is influenced by collisional and electrostatic forces. Above 130 km altitude, ion-neutral collisions are rare and the plasma tends to be tied to the magnetic field lines. In this region only the magnetic field aligned components of the acoustic disturbance influences the plasma concentration. Below 120 km altitu… more
Date: June 1, 1982
Creator: Bernhardt, P. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Fast-wave heating of a reactor plasma: consideration of two frequency regimes

Description: Fast-wave heating at omega = n omega/sub ci/, n = 1 or 2, is well suited to heating intermediate-size tokamaks such as ATC and PLT, but for significantly larger machines, the frequency spectrum becomes thickly packed with these modes. Adequate mode selection could require elaborate antennas; otherwise, mode overlap may produce surface heating of the plasma due to strong near fields at the antennas. On the other hand, the large minor radius and high plasma density in next-generation tokamaks wil… more
Date: October 1, 1976
Creator: Stix, T. H.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

A study of the propagation of ulf electromagnetic fields in collisional, inhomogeneous, magnetized plasmas

Description: The propagation of ultralow-frequency (ulf) electromagnetic signals (Alfven and magnetosonic waves) in collisional, inhomogeneous, magnetized plasmas is analyzed by numerical simulation. The problem is formulated from a Maxwell-equation orbit-theory approach rather than from a magnetohydrodynamic point of view, and the problem is numerically treated in a fully time-dependent manner. Boundary-value-problem behavior is distinguished from initial-value-problem behavior. The propagation of two-dime… more
Date: February 1, 1987
Creator: Borovsky, J. E.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Toroidal effects on propagation, damping, and linear mode conversion of lower hybrid waves

Description: A common simplifying assumption made in the consideration of radio-frequency heating of tokamaks near the lower hybrid frequency is that the wave-length imposed by the coupling device parallel to the magnetic field is not modified by gradients along the field. In the present calculation, the parallel wave-length is allowed to vary, and important effects are found on wave penetration and damping if the toroidal aspect ratio (R/sub major//r/sub minor/) is less than approx. 5. The calculation show… more
Date: September 1, 1980
Creator: Ignat, D. W.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Observation of ballooning instabilities with medium toroidal mode number in high temperature tokamak plasmas

Description: A beta degradation event in a high {beta}p, TFTR tokamak plasma is analyzed with X-ray and electron cyclotron emission (ECE) imaging techniques. Medium-n (toroidal mode number) instabilities with ballooning characteristics are observed near and within the q =1.5 surface during a slow degradation in the plasma {beta} and precede a sudden partial collapse in the central plasma pressure. This is the first reported observation of a ballooning instability in the interior of a large, collisionless to… more
Date: August 1, 1992
Creator: Nagayama, Y.; Manickam, J.; Fredrickson, E. D.; Bell, M.; Budny, R. V.; Cavallo, A. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

(Ion temperature gradient instability and transport: Progress report)

Description: Anomalous ion thermal conductivity remains in open physics issue for the present generation of high temperature Tokamaks. It is now believed to be due to the Ion Temperature Gradient (ITG or n{sub i}) instability. The production and identification of this instability is being studied in the simpler and experimentally convenient configuration of the steady state Columbia Linear Machine (CLM). The slab branch of this instability has been produced (by two different heating methods), identified and… more
Date: January 1, 1992
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Doppler model for adiabatic toroidal compressor driftwave frequency profiles

Description: Microwave and CO/sub 2/ laser scattering experiments on ATC (Adiabatic Toroidal Compressor) Tokamak have shown that there exists a spectrum of fluctuations with parallel bar f parallel bar = parallel bar ..omega../2..pi.. parallel bar less than or equal to 1 MHz at wavelengths lambda approximately 0.28 cm and with parallel bar f parallel bar less than or equal to 400 kHz for lambda approximately 1 cm. However, a typical maximum frequency calculated for given experimental density and temperature… more
Date: October 1, 1977
Creator: Koch, R.A. & Tang, W.M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Temporal evolution of lower hybrid waves in the presence of ponderomotive density fluctuations

Description: The propagation of lower hybrid waves in the presence of ponderomotive density density fluctuations is considered. The problem is treated in two dimensions and, in order to be able to correctly impose the boundary conditions, the waves are allowed to evolve in time. The fields are described by i upsilon/sub tau/ - ..integral.. upsilon/sub xi/d/sub zeta/ + upsilon/sub zeta zeta/ + upsilon//sup 2/ upsilon = 0 where upsilon is proportional to the electric field, tau to time, and zeta and xi measur… more
Date: June 1, 1980
Creator: Karney, C.F.F.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Investigation of global Alfven instabilities in TFTR

Description: Toroidal Alfven Eigenmodes (TAE) were excited by the energetic neutral beam ions tangentially injected into TFTR plasmas at low magnetic field such that the injection velocities were comparable to the Alfven speed. The modes were identified by measurements from Mirnov coils and beam emission spectroscopy (BES). TAE modes appear in bursts whose repetition rate increases with beam power. The neutron emission rate exhibits sawtooth-like behavior and the crashes always coincide with TAE bursts. Thi… more
Date: January 1, 1992
Creator: Wong, K. L.; Paul, S. F.; Fredrickson, E. D.; Nazikian, R.; Park, H. K.; Bell, M. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Output power enhancement of ac Raman free-electron laser

Description: The ac free-electron laser (ac FEL) uses an ac (temporally oscillating but spatially uniform) field as the pump source with the hope that electromagnetic radiation will be produced with wavelength shorter than that can be generated by a conventional magnet FEL. The ac field can be provided by a superconducting cavity or by a plasma wave. In this note, the effects of the thermal motion of the electron beam on the linear gain and the nonlinear saturated output power in a Raman-regime ac FEL with … more
Date: January 1, 1987
Creator: Yan, Y.T.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Generation of radiation by intense plasma and electromagnetic undulators

Description: This is a second year progress report which details the work on the generation of radiation by intense plasma and electromagnetic undulators being carried out at UCLA. The status of the experimental work is described and the future directions are outlined. We have completed the first phase of experiments on the plasma wiggler generation and characterization. Suitability of a {null}-pinch as a plasma source was investigated in great detail. It is found that a{sub w} of a few percent can be excit… more
Date: January 1, 1989
Creator: Joshi, C.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

The application of X-mode reflectometry to the study of large scale fluctuations in TFTR

Description: It has been suggested for some time that microwave reflectometry, has the potential for measuring the large scale structure of density fluctuations in tokamak turbulence with greatly improved spatial resolution over existing scattering techniques. The motivation for developing fluctuation diagnostics with improved spatial resolution of large scale structures is that such fluctuations may potentially account for the anomalous particle and energy transport observed in tokamaks. On TFTR we now hav… more
Date: March 1, 1993
Creator: Mazzucato, E. & Nazikian, R.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Microwave reflectometry for the study of density fluctuations in tokamak plasmas

Description: The effect of small scale density fluctuations on the propagation of electromagnetic waves in an inhomogeneous magnetized plasma in the presence of a cutoff is investigated. It is shown that, provided the fluctuation scale length is greater than the free space wavelength of an incident plane wave, the scattered field is strongly enhanced from fluctuations near the turning point. Numerical results for wave propagation in a tokamak plasma demonstrate the feasibility of reflectometry for the local… more
Date: December 1, 1990
Creator: Mazzucato, E. & Nazikian, R.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

The role of plasma rotation on MHD instabilities in tokamaks

Description: An improved analysis of the linear stage of the internal kink mode has been developed to include plasma rotation and finite aspect ratio effects. The linear instabiliy growth rates are increased by the plasma rotation. A pseudo-variational, bilinear formalism is used to discretize the linear instability equations; Fourier decomposition is used in the periodic coordinate, and a mixed-finite element procedure is adopted in the radial direction. The numerical studies with the resulting PEST-like c… more
Date: January 1, 1993
Creator: Varadarajan, V. & Miley, G.H.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
Back to Top of Screen