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1994
Earlier two-dimensional (radial and poloidal angle), analytically tractable ion kinetic models of the scrape-off layer (SOL) in which a steady state is achieved by balancing the streaming loss of ions to the divertor target plates with the radial diffusion of ions from the core are unable to distinguish between limited and diverted plasmas. The mod…
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1993
An important conclusion of earlier work using the ballooning representation is that shear damping of plasma drift waves may be suppressed in a torus. This application of the formalism requires that the diamagnetic frequency have a maximum and implies that drift modes can exist only at this maximum. Here we show that there is a far more general clas…
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1993
The magnetoacoustic cyclotron instability is a mechanism by which waves on the perpendicular fast Alfvén-ion Bernstein branch can be excited through cyclotron resonance with an energetic ion population. It is a candidate emission mechanism for the superthermal ion cyclotron radiation, apparently associated with the products of fusion reactions, th…
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1993
Low-aspect-ratio tokamaks offer both the economic advantage of smaller size and a number of physics advantages which are not available at conventional aspect ratio. The Small Tight Aspect Ratio Tokamak (START) [Fusion Technology 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (North-Holland, Amsterdam, 1991), Vol. 1, p. 353] was conceived a…
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1993
Nearly all kinetic treatments of fast wave minority heating of inhomogeneous plasma in the cyclotron range of frequencies assume the magnetic field varies in the direction perpendicular to the magnetic field. However, the toroidal magnetic field of a tokamak varies along a field line due to the rotational transform and causes a small number of trap…
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1993
Both neoclassical theory and certain turbulence theories of particle transport in tokamaks predict the existence of bootstrap (i.e., pressure-driven) currents. Two new applications of this form of noninductive current are considered in this work. In the first, an earlier model of the nonlinearly saturated m= 1 tearing mode is extended to include th…
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1993
It can be shown that whistler waves with low parallel phase velocity can be subject to strong cyclotron damping, even when the wave frequency is well below the cyclotron frequency. This resonance arises as a result of the Doppler effect which is proportional to the plasma density and increases the frequency experienced by electrons moving in the op…
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1992
This spectrometer was designed to give access to a wide range of Bragg angles and crystal focal lengths while using the Rowland circle radius as a free parameter. Stability is achieved using a rigid beam or “Rowland chord,” which provides a reference axis for all the critical alignments, the chord length being variable between about 0.2 and 5 m…
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1992
The superior etendu available from a Fabry-Perot spectrometer is also accessible when used in reflective mode in producing a narrow bandwidth rejection, or “notch,” filter. We consider the instrumental defects and the practical effects involved in realizing a useful device. A simple figure of merit is obtained which allows the Fabry-Perot chara…
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1992
09The thin beam model of an axis-encircling relativistic electron beam in a uniform, constant, external magnetic field in a cylindrical waveguide is used to develop a unified theory of the various interactions of such a beam with the electromagnetic field. The model includes the gyrotron interaction (longitudinal displacement of the beam) and the p…
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