Experiments on the Passage of a Shock Wave through a Magnetic Field

S>An investigation was made of the over-all conditions required for hydromagnetic interactions to occur between the rapidly moving portion of gas behind a strong shock in argon produced in a combustion-driven shock tube and the magnetic field of a short coil wound symmetrically around the tube. The general design considerations are given in which it was necessary to choose a geometry such that the emf caused by motional induction was not offset by a mere separation of charge, because if this occurs, the current flow ceases after a very short interval. Photographic observations were made of the shock waves by focusing a camera on the glass observation section of the shock tube, darkening the laboratory, and opening the camera shutter. Electromagnetic measurements were made to determine the density of the currents circulating in the plasma by using short pickup coils wound around the shock tube downstream from the magnetic coil at 3-cm intervals, then studying the waveforms of the induced emf's registered on oscilloscopes. Although the Lundquist number, Lu, was used as a working parameter, according to theory the interpretation of the results in terms of Lu can only be expected to be unambiguous when the magnetic Reynolds number, R/more » sub M/, is large. When R/sub M/ is small the inducing field is hardly modified by the motion and then it is a straightforward matter to compare directly the inertial term with the j x B term in the equation of motion. (B.O.G.)« less