The use of the Phillips–Tikhonov regularization is proposed for numerically stabilizing the ill-conditioned plasma image reconstructions. An objective function to be minimized leads to a linear estimator of the image intensity distribution and, with the aid of the singular value decomposition, makes it possible to use the generalized cross validation for optimizing a regularization parameter. An excellent behavior of the estimator with computational facility is obtained on the Hα emission computerized tomography of a toroidal plasma.

An overview of the research and development of imaging bolometers giving a perspective on the applicability of this diagnostic to a fusion reactor is presented. Traditionally the total power lost from a high temperature, magnetically confined plasma through radiation and neutral particles has been measured using one dimensional arrays of resistive bolometers. The large number of signal wires associated with these resistive bolometers poses hazards not only at the vacuum interface, but also in the loss of electrical contacts that has been observed in the presence of fusion reactor levels of neutron flux. Imaging bolometers, on the other hand, use the infrared radiation from the absorbing metal foil to transfer the signal through the vacuum interface and out from behind a neutron shield. Recently a prototype imaging bolometer known as the InfraRed imaging Video Bolometer has been deployed on the JT-60U tokamak which demonstrates the ability of this diagnostic to operate in a reactor environment. The application of computed tomography demonstrates the ability of one imaging bolometer with a semi-tangential view to produce images of the plasma emissivity. In addition, new detector foil development promises to strengthen the foil and increase the sensitivity by an order of magnitude.

Spectrum parameter estimation concerning a stationary and homogeneous random field is examined in terms of quantities obtainable from a pair of fixed probes. The estimators of the mean wave number and the wave-number spectral width are derived by relating wave-number spectral moments to spatial derivatives of the complex covariance of the field, the effect of finite probe size being taken into account. The estimate biases associated with the probe separation can be greatly reduced by employing an algorithm based on the polar-form representation of the complex covariance, while the variances of the estimates have a tendency to be enhanced with the decrease of the probe separation. An optimum range of the probe separation is theoretically determined.

Tomographic reconstruction of the emission profile is a typical ill-posed inversion problem. It becomes troublesome in fusion plasma diagnostics because the possible location/direction of the observation is quite limited. In order to overcome the difficulty, many techniques have been developed. Among them, series expansion methods are based on decomposing the emission profile with orthogonal or nearly orthogonal basis patterns. Since it is possible to ignore the surplus components with higher spatial frequency, this type of method is robust against noise issues. Two topics are discussed in this article. The first issue is the comparison of the basis systems themselves. Conventional one of Fourier-Bessel and a new one of the so-called Laplacian eigen function are compared from the viewpoint of the capability of expressing the patterns that appear in the fusion plasma experiment. The second issue is the application to the tangential viewing imaging system. It is shown that, even from the limited information, tomographic reconstruction can be adequately performed with appropriate use of the regularization, especially with the use of the L1 regularization.

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