Possibility of using active secondary charge-exchange particle diagnostics for measuring the magnetic field direction in
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Possibility of Using Active Secondary Charge-Exchange Particle Diagnostics for Measuring the Magnetic Field Direction in the Plasma of a Magnetic Fusion Reactor A. A. Medvedev and V. S. Strelkov Nuclear Fusion Institute, Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia Received June 10, 2004; in final form, November 25, 2005
Abstract—An active particle diagnostic method based on the secondary charge exchange of hydrogen atoms of a probing (diagnostic) beam is proposed for local measurements of the magnetic field direction in the plasma of a thermonuclear fusion reactor. Experiments with new-generation large devices require searching for novel methods for measuring the direction of the total magnetic field in a plasma at different points along the radius of the plasma column. The main idea of the method proposed, which holds great promise for large devices, is outlined. The possibility of using the method on ITER—a large fusion reactor that is now at the design stage— is illustrated by carrying out relevant numerical simulations. The results obtained for one of the main discharge scenarios, with the injection geometry and probing beam energy (100 eV) that are now adopted for the ITER design, show that the method can provide local measurements of the magnetic field direction (the magnetic pitch angle) and of the spatial variations of the field vector. Further analysis has revealed, however, that, from the standpoint of signal intensity and signal-to-noise ratio, it is expedient to increase the energy of the beam atoms to 200–250 keV. With such probing beams, the method ensures a spatial (radial) resolution of about 10 cm in the plasma core during a signal acquisition time of 10 ms. The magnetic pitch angle can be measured with an accuracy of 5 × 10–3 rad. An important advantage of the method proposed is its ability to directly measure the pitch angle of the magnetic field lines. PACS numbers: 52.70.Nc, 52.55.Fa DOI: 10.1134/S1063780X06050060
1. INTRODUCTION The development of new methods for measuring the safety factor q is among the most complicated tasks with which the physicist teams developing diagnostic systems for next-generation tokamaks are faced. In most cases, the safety factor q is determined by using the data from local measurements of the direction of the magnetic field in a plasma. However, there is some doubt as to whether the existing diagnostic techniques will provide as reliable and accurate measurement results in fusion reactors as they do in modern tokamaks. For instance, attempts to suit the motional stark effect (MSE) diagnostics, which is widely used in present-day experiments, to an ITER-scale device run into technical difficulties, which are so serious that the possibility of implementing this diagnostics in reactors becomes questionable. This is why the need to search for alternative approaches is constantly emphasized. One such alternative method is proposed in the present paper. Secondary charge-exchange (SCX) atomic fluxes were first obs
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