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Small-scale density fluctuations in the adiabatic toroidal compressor

Description: A new class of density fluctuations has been observed in the ATC tokamak by using spectral analysis of scattered microwaves. The observed frequency spectrum is consistent with that of drift waves with amplitudes that are maximum in the wavelength range 0.5 to 1.0 cm where finite ion Larmor radius effects are important for plasma stability. The total density fluctuation is n tilde/sub e/ greater than or equal to 5 x 10$sup -3$ anti n/sub e/. It is estimated that these fluctuations could account for a large fraction of the electron energy losses of the ATC discharge. (auth)
Date: February 1, 1976
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Propagation of a Gaussian beam in a nonhomogeneous plasma

Description: The asymptotic theory of Choudhary and Felsen on the propagation of scalar inhomogeneous waves in two-dimensional isotropic media is extended to the case of three-dimensional vector fields. The theory is applied to the propagation of Gaussian beams in nonhomogeneous media. The wave trajectory equations are then reformulated for anisotropic media and used for tracking a Gaussian beam in a tokamak plasma. 14 refs., 5 figs.
Date: June 1, 1989
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Microturbulence in the PLT Tokamak

Description: By heterodyne detection of scattered microwaves, density fluctuations have been observed in the PLT tokamak in the range of wavelengths 0.2-2 cm and with frequencies up to 200 to 300 kHz. The flux of runaway electrons onto the limiter was modulated in the same range of frequencies. The level of turbulence was enhanced by the injection of energetic neutrals; and for ion temperatures in excess of 4 keV, a new type of oscillation was observed.
Date: April 1, 1980
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Transport of electron thermal energy in high temperature plasmas

Description: The nature of the anomalous transport of electron thermal energy in existing experiments on magnetically confined toroidal plasmas is discussed and a new form of the relevant electron thermal conductivity, that is consistent with the observed temperature profiles, is presented.
Date: May 1, 1979
Creator: Coppi, B. & Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Density rise experiment on PLT

Description: The evolution of the density profile in PLT during intense gas puffing is documented and analyzed. Measurements of the spectrum of low energy edge neutrals and of the change in central neutral density indicate that charge-exchange processes alone cannot account for the central density rise. The transient density profile changes can be reproduced numerically by a diffusivity of approx. 10/sup 4/ cm/sup 2//s, and a spatially averaged inward flow of 10/sup 3/ cm/s. These transport coefficients are 10 ..-->.. 10/sup 2/ times larger than neoclassical. The ion energy confinement is reduced, the small scale density fluctuations are increased, and runaway electrons losses are increased during the density rise.
Date: May 1, 1982
Creator: Strachan, J.D.; Bretz, N. & Mazzucato, E.
Partner: UNT Libraries Government Documents Department

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 localized measurement of density fluctuations in the range k {sub {perpendicular}} {rho}{sub i} {much lt} 1. 19 refs., 6 figs,
Date: December 1, 1990
Creator: Mazzucato, E. & Nazikian, R.
Partner: UNT Libraries Government Documents Department

Damping of electron cyclotron waves in dense plasmas of a compact ignition tokamak

Description: Absorption of electromagnetic waves by hot and dense plasmas is investigated in the electron cyclotron range of frequency. It is shown that the strong reduction of the damping of the extraordinary mode, caused by finite Larmor radius effects on waves propagating perpendicularly to the magnetic field, becomes insignificant at large values of the parallel component of the refractive index. With an appropriate form of the relativistic dispersion relation which includes high order Larmor radius terms, heating of dense plasmas in a Compact Ignition Tokamak is investigated. It is shown that by using the extraordinary mode with oblique propagation and frequency of 190 GHz it is possible to bring to thermonuclear ignition a dense ohmic plasma with a toroidal magnetic field of 105 kG and a central density of 1 x 10/sup 15/ cm/sup -3/. 11 refs., 11 figs.
Date: June 1, 1987
Creator: Mazzucato, E.; Fidone, I. & Granata, G.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating of a tokamak reactor at down-shifted frequencies

Description: The absorption of electron cyclotron waves in a hot and dense tokamak plasma is investigated for the case of the extraordinary mode for outside launching. It is shown that, for electron temperatures T/sub e/ greater than or equal to 5 keV, strong absorption occurs for oblique propagation at frequencies significantly below the electron gyrofrequency at the plasma center. A new density dependence of the wave absorption is found which is more favorable for plasma heating than the familiar n/sub e//sup -1/ scaling.
Date: January 1, 1985
Creator: Fidone, I.; Giruzzi, G. & Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Relativistic effects on cyclotron wave absorption by an energetic electron tail in the PLT tokamak

Description: Electron cyclotron wave absorption by mildly relativistic electrons in the low density regime of the PLT tokamak is investigated. Appreciable wave damping is found for vertical propagation at frequencies of 50, 60, and 70 GHz when the spatially constant cyclotron frequency is 89 GHz. The perpendicular temperature T/sub perpendicular/(v/sub parallel/) of the fast tail is also measured from emission of radiation in the same direction. The results obtained are in satisfactory agreement with the theory of wave emission and absorption.
Date: July 1, 1984
Creator: Mazzucato, E.; Efthimion, P. & Fidone, I.
Partner: UNT Libraries Government Documents Department

A Midsize Tokamak As Fast Track To Burning Plasmas

Description: This paper presents a midsize tokamak as a fast track to the investigation of burning plasmas. It is shown that it could reach large values of energy gain (≥10) with only a modest improvement in confinement over the scaling that was used for designing the International Thermonuclear Experimental Reactor (ITER). This could be achieved by operating in a low plasma recycling regime that experiments indicate can lead to improved plasma confinement. The possibility of reaching the necessary conditions of low recycling using a more efficient magnetic divertor than those of present tokamaks is discussed.
Date: July 14, 2010
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Localized Measurement of Turbulent Fluctuations in Tokamaks with Coherent Scattering of Electromagnetic Waves

Description: Localized measurements of short-scale turbulent fluctuations in tokamaks are still an outstanding problem. In this paper, the method of coherent scattering of electromagnetic waves for the detection of density fluctuations is revisited. Results indicate that the proper choice of frequency, size and launching of the probing wave can transform this method into an excellent technique for high-resolution measurements of those fluctuations that plasma theory indicates as the potential cause of anomalous transport in tokamaks. The best spatial resolution can be achieved when the range of scattering angles corresponding to the spectrum of fluctuations under investigation is small. This favors the use of high frequency probing waves, such as those of far infrared lasers. The application to existing large tokamaks is discussed.
Date: August 19, 2002
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Numerical Study of Microwave Reflectometry in Plasmas with 2D Turbulent Fluctuations

Description: This paper describes a numerical study of the role played by 2D turbulent fluctuations in microwave reflectometry -- a radar technique for density measurements using the reflection of electromagnetic waves from a plasma cutoff. The results indicate that, if the amplitude of fluctuations is below a threshold which is set by the spectrum of poloidal wavenumbers, the measured backward field appears to originate from a virtual location behind the reflecting layer, and to arise from the phase modulation of the probing wave, with an amplitude given by 1D geometric optics. These results suggest a possible scheme for turbulence measurements in tokamaks, where the backward field is collected with a wide aperture antenna, and the virtual reflecting layer is imaged onto the plane of an array of detectors. Such a scheme should be capable of providing additional information on the nature of the short-scale turbulence observed in tokamaks, which still remains one of the unresolved issues in fusion research.
Date: February 1, 1998
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Microwave Reflectometry for Magnetically Confined Plasmas

Description: This paper is about microwave reflectometry -- a radar technique for plasma density measurements using the reflection of electromagnetic waves by a plasma cutoff. Both the theoretical foundations of reflectometry and its practical application to the study of magnetically confined plasmas are reviewed in this paper. In particular, the role of short-scale density fluctuations is discussed at length, both as a unique diagnostic tool for turbulence studies in thermonuclear plasmas and for the deleterious effects that fluctuations may have on the measurement of the average plasma density with microwave reflectometry.
Date: February 1, 1998
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

The importance of the toroidal magnetic field for the feasibility of a tokamak burning plasma experiment

Description: The next step in the demonstration of the scientific feasibility of a tokamak fusion reactor is a DT burning plasma experiment for the study and control of self-heated plasmas. In this paper, the authors examine the role of the toroidal magnetic field on the confinement of a tokamak plasma in the ELMy H-mode regime--the operational regime foreseen for ITER.
Date: March 22, 2000
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Microwave Imaging Reflectometry for the Visualization of Turbulence in Tokamaks

Description: Understanding the mechanism of anomalous transport in magnetically confined plasmas requires the use of sophisticated diagnostic tools for the measurement of short-scale turbulent fluctuations. This paper describes the conceptual design of an experimental technique for the global visualization of density fluctuations in tokamaks. The proposed method is based on microwave reflectometry and consists in using a large diameter probing beam, collecting the reflected waves with a large aperture antenna, and forming an image of the reflecting plasma layer onto a 2D array of microwave receivers. Based on results from a series of numerical simulations, the theoretical feasibility conditions of the proposed method are discussed.
Date: December 16, 1999
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Microwave Imaging Reflectometry for the Measurement of Turbulent Fluctuations in Tokamaks

Description: This article describes a numerical study of microwave reflectometry for the measurement of turbulent fluctuations in tokamak-like plasmas with a cylindrical geometry. Similarly to what was found previously in plane-stratified plasmas, the results indicate that the characteristics of density fluctuations cannot be uniquely determined from the reflected waves if the latter are allowed to propagate freely to the point of detection, as in standard reflectometry. Again, we find that if the amplitude of fluctuations is below a threshold that is set by the spectrum of poloidal wave numbers, the local characteristics of density fluctuations can be obtained from the phase of reflected waves when these are collected with a wide aperture antenna, and an image of the cutoff is formed onto an array of phase-sensitive detectors.
Date: February 19, 2004
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

About the Toroidal Magnetic Field of a Tokamak Burning Plasma Experiment with Superconducting Coils

Description: In tokamaks, the strong dependence on the toroidal magnetic field of both plasma pressure and energy confinement is what makes possible the construction of small and relatively inexpensive burning plasma experiments using high-field resistive coils. On the other hand, the toroidal magnetic field of tokamaks using superconducting coils is limited by the critical field of superconductivity. In this article, we examine the relative merit of raising the magnetic field of a tokamak plasma by increasing its aspect ratio at a constant value of the peak field in the toroidal magnet. Taking ITER-FEAT as an example, we find that it is possible to reach thermonuclear ignition using an aspect ratio of approximately 4.5 and a toroidal magnetic field of 7.3 T. Under these conditions, fusion power density and neutron wall loading are the same as in ITER [International Thermonuclear Experimental Reactor], but the normalized plasma beta is substantially smaller. Furthermore, such a tokamak would be able to reach an energy gain of approximately 15 even with the deterioration in plasma confinement that is known to occur near the density limit where ITER is forced to operate.
Date: February 20, 2002
Creator: Mazzucato, E.
Partner: UNT Libraries Government Documents Department

Plasma density measurements using FM-CW millimeter wave radar techniques

Description: Modified FM-CW radar techniques using swept millimeter-wave oscillators are useful for determining when a particular density has been reached in a plasma. Narrowband measurements on the Princeton Large Torus (PLT) demonstrate the suitability of these techniques for controlling high-power auxiliary plasma heating systems. Broadband measurements using these same techniques are proposed, by which the density profile could be determined.
Date: September 1, 1980
Creator: Doane, J.L.; Mazzucato, E. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

The radial scale length of turbulent fluctuations in the main core of TFTR plasmas

Description: A new theory of microwave reflectometry in tokamaks has been developed which accounts for all the major characteristics of waves reflected from strong fluctuations near the cutoff layer. The theory has been used for studying the turbulence in the main core of neutral beam heated plasmas of the TFTR tokamak in the supershot regime. The results indicate that the radial correlation length of density fluctuations is a weak decreasing function of beam power, from [approximately]4 cm in Ohmic to [approx]2 cm at 14 MW of heating power. This corresponds to the range of wavelengths k[sub [perpendicular]][rho][sub i][approx]0.1--0.3. Over the same interval of heating powers, the level of density fluctuations is observed to steadily increase with beam power by more than an order of magnitude. This trend is inconsistent with mixing length estimates of the fluctuation level.
Date: July 1, 1993
Creator: Mazzucato, E. & Nazikian, R.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating at down-shifted frequencies in existing tokamak devices

Description: Plasma heating in existing tokamak devices by electron cyclotron waves with frequency (f) significantly smaller than the electron gyrofrequency (f/sub c/) is investigated for the case of Maxwellian plasmas. It is shown that for central electron temperatures larger than 3 keV, strong absorption of extraordinary waves can occur at values of toroidal field for which the condition f = f/sub c/ is not satisfied in the plasma region. The cases of f = 60 GHz and f = 100 GHz are discussed for the PLT and TFTR devices as representative of medium (approx. =30 kG) and high (approx. =50 kG) magnetic field tokamaks, respectively. Numerical calculations with a ray tracing code indicate that most of the rf energy is absorbed in a central plasma region. These results are of practical interest because they significantly simplify the main technical problem of ECH in a tokamak reactor, i.e., the development of high frequency and high power microwave sources.
Date: June 1, 1985
Creator: Mazzucato, E.; Fidone, I.; Giruzzi, G. & Krivenski, V.
Partner: UNT Libraries Government Documents Department

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 have operational a four channel X-mode reflectometer system comprising of three fixed frequency channels at 140, 132.5, and 125 GHz and a able frequency channel scanning between 110--123 GHz. Each channel detects fluctuations from a region on the equatorial plane of the plasma torus with spatial resolution of [approx]5 cm in the poloidal direction and [approx]1 cm in the radial direction. Properties of the plasma turbulence are inferred from the amplitude and spectral coherence of phase fluctuations impressed on the reflected wave by density irregularities at or near the cutoff. Experimental results are presented which show the existence of previously unobserved large scale (k[perpendicular][rho][sub i]<<1) random and coherent density fluctuations in the Ohmic and Supershot regimes of TFTR.
Date: March 1, 1993
Creator: Mazzucato, E. & Nazikian, R.
Partner: UNT Libraries Government Documents Department

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 have operational a four channel X-mode reflectometer system comprising of three fixed frequency channels at 140, 132.5, and 125 GHz and a able frequency channel scanning between 110--123 GHz. Each channel detects fluctuations from a region on the equatorial plane of the plasma torus with spatial resolution of {approx}5 cm in the poloidal direction and {approx}1 cm in the radial direction. Properties of the plasma turbulence are inferred from the amplitude and spectral coherence of phase fluctuations impressed on the reflected wave by density irregularities at or near the cutoff. Experimental results are presented which show the existence of previously unobserved large scale (k{perpendicular}{rho}{sub i}<<1) random and coherent density fluctuations in the Ohmic and Supershot regimes of TFTR.
Date: March 1, 1993
Creator: Mazzucato, E. & Nazikian, R.
Partner: UNT Libraries Government Documents Department

Turbulent fluctuations in the main core of TFTR plasmas with negative magnetic shear

Description: Turbulent fluctuations in plasmas with reversed magnetic shear have been investigated in TFTR. Under intense auxiliary heating, these plasmas are observed to bifurcate into two states with different transport properties. In the state with better confinement, it has been found that the level of fluctuations is very small throughout most of the region with negative shear. By contrast, the state with lower confinement is characterized by large bursts of fluctuations which suggest a competition between the driving and the suppression of turbulence. These results are consistent with the suppression of turbulence by the ExB velocity shear.
Date: April 1, 1997
Creator: Mazzucato, E.; Beer, M. & Bell, M.G.
Partner: UNT Libraries Government Documents Department