Generation of 600 T by electromagnetic flux compression with improved implosion symmetry

Abstract

We have developed a device for generating ultrahigh magnetic fields by means of electromagnetic flux compression. The device that we call “feed gap compensator” is a flux concentrator that consists of a thick-walled copper cylinder with a number of thin radial slits. This is inserted between the primary coil and the liner; it has resulted in a substantial improvement of the implosion symmetry that is normally disturbed by the feed gap of the primary coil. A maximum field exceeding 600 T can be generated reproducibly by using this device. Because of the improved symmetry of the liner motion, we observed turnaround phenomena not only in the wave form of the magnetic field but also in the photographs of the liner that are taken by a high-speed image converter camera. The final implosion speed and the turnaround radius have been determined by calculating the magnetic flux from a combination of framing camera data and the measured field. It is confirmed that the turnaround field is a function of the implosion speed; this function is given by the particle speed of the shock wave associated with the pressure pulse induced by the magnetic field. Further optimization of the flux compression system is discussed with a view to obtaining higher fields that are suitable for application in experiments.