185 research outputs found
First tomographic reconstructions and a study of interference filters for visibleâlight tomography on RTP
Possible mechanism responsible for observed impurity outward flow under radio frequency heating
The effect of poloidal asymmetry of impurities on impurity transport driven
by electrostatic turbulence in tokamak plasmas is analyzed. It is found that in
the presence of in-out asymmetric impurity populations the zero-flux impurity
density gradient (the so-called peaking factor) is significantly reduced. A
sign change in the impurity flux may occur if the asymmetry is sufficiently
large. This may be a contributing reason for the observed outward convection of
impurities in the presence of radio frequency heating. The effect of in-out
asymmetry is most significant in regions with low temperature gradients. In the
trapped electron mode dominated case also an up-down asymmetry can lead to a
sign change in the peaking factor from positive to negative. The effect of ion
parallel compressibility on the peaking factor is significant, and leads to
positive peaking factors in regions with high temperature gradients, even in
the presence of in-out asymmetry.Comment: 19 pages, 14 figure
Development of an automated method for in situ measurement of the geometrical properties of the ITER bolometer diagnostic
Optimization of apertures and collimators for multi-channel plasma diagnostics
Aperture, pin-hole and collimator detection systems are often used in plasma diagnostics, for example, in soft x-ray detection and bolometer systems. In this article the simultaneous optimization of viewing-beam overlap and light yield is considered in multi-channel aperture and collimator systems for two-dimensional (2D) tomography. This article briefly highlights the relation between beamwidth overlap and spatial aliasing in tomography, and how aliasing can be avoided in theory and in practice. Three-dimensional (3D) single-channel aperture and collimator systems can be approximated by a combination of two planar systems if the aperture is rectangular. Three ways to optimize beamwidth overlap and light yield for planar aperture and collimator systems are considered in detail: overlap of the angular etendue at the full width at half maximum (FWHM), overlap of the geometric function at the FWHM a certain distance from the aperture, and arbitrary overlap for a given maximum beamwidth. The combination of 2D effects from all three optimization methods were used in the design of 3D apertures for a new multi-channel bolometer camera on the Joint European Torus tokamak. The resulting apertures are complex, but the new camera has several advantages over previous cameras. (C) 2002 American Institute of Physics
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