(a) Twisted toroidally closed magnetic field lines form nested flux surfaces. (b) Experimentally determined Poincaré plot showing a poloidal cut view of multiple nested flux surfaces with three islands in the outer region of the WEGA stellarator (Ref. 1).
Two designs for an electron gun are shown, accelerating the electrons from a heated and negatively charged tungsten filament with a metal cup with a (a) hole in flight direction and with a (b) mesh in flight direction. The anodes are on the same potential as the plasma vessel to screen electric fields. (c) Cut view of the vacuum chamber with magnetic field in axial (vertical) direction where preliminary tests of the electron guns were performed.
Electron current emitted from the tungsten filament (shaded bar) and current in the electron beam (full bar) for different heating powers.
(a) Measured cross sectional area for different pressures of argon at after a flight distance of shown for two electron gun designs operated at . (b) Calculated and measured for different magnetic field strengths with electron gun design 1.
(a) Length of the visible beam calculated from the number of visible orbits in argon vs pressures and tangential view on the visualized field lines for (b) and (c) with electron gun design 1.
(a) Device setup with toroidal field coils (dark blue), vacuum vessel (gray), luminescent trace of the electron beam (magenta), four observation cameras (black), and a mount with six reference points (white dots with rings). (b) Sketch of principle of photogrammetry with two pinhole cameras observing one object point.
Photo of one visualized magnetic field line with five transitions in the field of view and six reference points inside the torus.
Trace measurement principle shown with two images of the same field line section. Red and yellow points represent border points of the trace while the red line is the projection of a calculated light ray of point 1 of image (a) in the field of view of image (b).
Poincaré plot of the first to fourth intersection points in a poloidal plane of an electron drift path for two magnetic field configurations with (red) and (blue) calculated with the W7 code.
Comparison of measured data (red) with numerically calculated drift trajectories (orange) in a (a) top view and a (b) tangential view on the plasma vessel contour (dark blue). The black figure represents the connected six reference points.
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