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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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1992
This Brief Communication investigates the influence of toroidal effects (due to the coupling of various poloidal harmonics) on the nonlinear saturation of the m = 1 island. Bounds are obtained relating the aspect ratio, the shear at the q= 1 surface, and the saturated island width. Provided these bounds are satisfied, it is then found that the cyli…
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1992
Intense superthermal ion cyclotron emission (ICE) has been observed from tokamak plasmas. The power spectrum displays narrow peaks at multiple harmonics of the background ion cyclotron frequency [Cottrell and Dendy, Phys. Rev. Lett. 60, 33 (1988)] in Ohmic deuterium plasmas, and the radiation appears to be driven by the fusion ion population in the…
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1992
The experimental performance of a high-brightness neutral-beam system is described which has been designed and manufactured by Culham Laboratory under contract to the Princeton Plasma Physics Laboratory. The neutral beam serves as a diagnostic on the PBX-M experiment and is used to perform studies of high-bet a, bean-shaped, neutral-beam-heated pla…
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1992
Impurities in fusion plasmas lead to a loss of reactivity by radiation and fuel dilution. 1 The impurity concentration in the plasma is determined both by the production rate and transport in the plasma, particularly the transport in the boundary layer. 1'2 In this layer impurities, usually starting as cold atoms or molecules, are ionised and heate…
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1992
The three-dimensional nonlinear kinetic equation for low collisionality tokamak plasmas with consistent consideration of neoclassical effects is obtained using an approach differing from the standard neoclassical theory technique. This allows treatment of large-banana widths and large inverse aspect ratios. The equation is suitable for computer mod…
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1992
Neural networks provide a new tool for the fast solution of repetitive nonlinear curve fitting problems. In this article we introduce the concept of a neural network, and we show how such networks can be used for fitting functional forms to experimental data. The neural network algorithm is typically much faster than conventional iterative approach…
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1992
A compact seven channel interferometer has been designed and built to measure electron density profiles in the COMPASS (compact assembly) tokamak. Two far-infrared (FIR) laser cavities are optically pumped with a single continuous-wave CO2 laser, generating two similar beams, with a small, tunable difference frequency (0.5-1.0 MHz). The COMPASS fac…
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1992
Laser-induced fluorescence (LIF) is a well established technique used to determine the neutral hydrogen density in fusion plasmas.There is a requirement to extend these measurements to the Divertor section of large plasma devices, but this is problematical due to the high levels of stray laser light and background plasma emission. Here we describe …
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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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