During the first year of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1 . O B J1.46T, I <800kA, ~S2.05, -0.7G%0.7. A new shape control algorithm, Eased on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates of 800 sec-', corresponding to a stability margin f=l.IS, have been stabilized. Ohmic H-modes, with energy confinement times reaching 8 h s , normalized beta (p ,aB/I> of 1.9 and z P R 8 9 -P of 2.4 have been obtained in singlenuB X-point deuterium discharges with the ion grad B drift towards the X-point. Limiter H-modes with maximum line averaged electron densities of 1 . 7~1 0~~m -~ have been observed in D-shaped plasmas with 360kASIp&00kA.

The TCV tokamak has obtained ohmic H-modes in virtually all diverted plasmas with the ion ∇B drift directed towards an X-point and in several elongated limiter plasmas. Troyon factors (β tor aB/I p ) up to 2 and line average densities up to 2.2×10 20 m −3 , corresponding to the Greenwald limit, have been obtained in diverted ELM-free H-modes. Quasi-stationary Hmodes lasting for the entire current flat top (1.5 s) have been obtained in the presence of regular ELMs. The occurrence and magnitude of ELMs have been found to depend on configurational parameters such as the position of the 'active' X-point in unbalanced double-null discharges and the plasma-wall separation in single-null discharges. These dependencies have permitted active control of ELM behaviour in TCV. A continuous spectrum of ELM amplitudes and frequencies has been observed, ranging from clearly identifiable type III ELMs to large, low-frequency ELMs which expel up to 12% of the stored energy and up to 7% of the particle content and are reminiscent of type I ELMs. A previously unknown, benign kind of ELM, with a maximum amplitude in the divertor region, has also been observed.

Third generation fan-beam computerized tomography ͑CT͒ scanners acquire data one entire projection at a time. The associated filtered-backprojection algorithm requires a computationally expensive pixel-dependent weight factor in the backprojector. Methods of simplifying the reconstruction include rebinning the fan-beam data to parallel projections. The rebinning can be separated into two steps: azimuthal interpolation, leading to the fan-parallel geometry, where data are unevenly spaced on radial lines through the origin of Radon space, and a subsequent axial interpolation to parallel data. Under appropriate view and projection sampling conditions, the azimuthal interpolation can be replaced by either data resorting or projection channel-dependent delays. This article investigates an arcsin algorithm to reconstruct an image directly from the fan-parallel data. Although it is shown that the algorithm cannot be exact, a natural approximation is described. The pre-and postconvolution weights, and the reconstruction filter, are derived analytically. Imaging results demonstrate that arcsin image quality matches that of parallel reconstruction. The fanparallel reconstruction method eliminates the resolution-compromising axial interpolation and the costly pixel-dependent backprojection weight. Further, an arcsin detector design is proposed for direct parallel reconstruction from fan-beam data. © 1999 American Association of Physicists in Medicine. ͓S0094-2405͑99͒00403-4͔

The problem of two-dimensional tomographic image reconstruction from fan-beam projections via shift-invariant filtering (convolution) followed by backprojection has a solution for two well known fan-beam parametrization classes. These parametrizations are associated either with equidistant collinear detector cells or with equi-angular fan rays. In this paper, the problem of finding all such fan-beam parametrizations is solved. Two new parametrization classes are found, which define new CT reconstruction algorithms. Two interpretations are given for the new parametrizations. First, the associated loci of equidistant detector cells are found by solving numerically the differential equations that characterize them. Application of the numerical approach also unveils a new detector geometry associated with one of the two previously known parametrization classes. Secondly, by mapping the parametrizations onto the familiar third-generation CT geometry, variable resolution samplings of the scan field of view are found. Also, the problem of CT image reconstruction on a fourth-generation scanner is addressed. Although it is found that the corresponding parametrization does not belong to the convolution solution set, a 'natural' shift-invariant filter decomposition is described that provides a close approximation to the reconstruction filter.

This paper r e v i w s the experimental status and recevt advances i n AlfvCn Wave Heating (AWH). We discuss the underlying physics of Alfven Wave Heating, as seen by the experiments. The use of AlfvCn Waves for plasna diagnosis is discussed. The results of plasna heating on TCA are s m a r i z e d . Apparent changes i n the current profile are inferred, caused by changes i n the evolving AlfvCn wave spectrun excited. The implications for AWH on larger devices are mentioned. KFrwoRDsAlfven Wave Heating; Tokamak; Kinetic Alfvgn Wave; Profile Cor?trol; Antema Systen; plasm Diagnostics; Tc9. IMTR3DilCTIONI n t h i s paper we shall review the recent experiwntal results obtained i n AlfvCn Wave Heating (AXH). The early experimental results have already been reviewed by Shohet (1978), and w shall not repeat that survey. An overview of the extensive theoretical mrk i n Lhis freqency range is beyond t h i s paper, and the current status has been very recently reviewed by Pppert and colleagues (1586). W e shall review the theoretical basis of .MX frm. the viewpint of the experimental observations made, and shall, i n f a c t , discover that mst of the imprtant concepts manifest themselves i n the results.