Der wendelnde Wasserstoffbogen
A hydrogen arc with a fixed lower and a movable upper end abruptly changes from its straight static form into a rotating conical helix when a critical current is exceeded. The chances of its winding becoming left or right-hand are equal if the earth magnetic field is compensated. A helix with a left winding, however, is always turning clockwise, a helix with a right winding counter-clockwise if looking axially in the direction of the expanding helical arc. The frequency of the rotation depends only on the current strength and is explained by the balance of the driving Lorentz forces due to the intrinsic magnetic field of the entire electrical circuit on one hand and the friction of the moving arc with its environment on the other. A corresponding model theory applied to measurements on a wall-stabilized H2-Arc with 10–15 A in a quartz tube of 10 mm radius yields a reasonable arc diameter of 2.23 mm. The observed independence of the rotation frequency on the length of the arc can be derived from the balance equations as well. By superimposing an external axial magnetic field to the rotating arc its rotation frequency and simultaneously its expansion increase if the external field is parallel to the intrinsic one and viceversa. The experimental results are in full agreement with calculations based upon the model including the effect of the external field as an additional independent variable.