Electromagnetic Flux Compression Technique Research Articles

Closing the hybridization charge gap in the Kondo semiconductor SmB6 with an ultrahigh magnetic field

We have investigated the high-frequency magnetoresistance of Kondo semiconductor ${\mathrm{SmB}}_{6}$ under ultrahigh magnetic fields generated by the electromagnetic flux-compression technique. The semiconductor-metal transition due to closing of the hybridization charge gap was observed at approximately 180 T. The critical magnetic field observed is substantially higher than that reported previously. At temperatures below around 10 K, another transition was observed at a lower field (approximately 80 T). We suggest that the observed 80-T transition relates with the energy scale of quasiparticles such as the spin polaron in the in-gap state.

Quantum limit cyclotron resonance in monolayer epitaxial graphene in magnetic fields up to 560 T: The relativistic electron and hole asymmetry

Electron-hole symmetry breaking of Dirac electrons has been evidenced as a well-resolved cyclotron resonance (CR) peak splitting at magnetic fields around 300-500 T in epitaxial monolayer graphene. The magnetic field was swept up to 560 T for the infrared CR by means of the electromagnetic flux compression technique in a 1000-T class megagauss generator. The authors argue that it is the CR mode repulsion, caused by the electron-electron correlation, which is responsible for the observed CR intensity transfer from the hole to the electron.

Note: An approach to 1000 T using the electro-magnetic flux compression.

The maximum magnetic field obtained by the electro-magnetic flux compression technique was investigated with respect to the initial seed magnetic field. It was found that the reduction in the seed magnetic field from 3.8 T to 3.0 T led to a substantial increase in the final peak magnetic field. The optical Faraday rotation method with a minimal size probe evades disturbances from electromagnetic noise and shockwave effects to detect such final peak fields in a reduced space of an inner wall of the imploding liner. The Faraday rotation signal recorded the maximum magnetic field increased significantly to the highest magnetic field of 985 T approaching 1000 T, ever achieved by the electro-magnetic flux compression technique as an indoor experiment.

Note: Experimental evidence of three-dimensional dynamics of an electromagnetically imploded liner

The time-dependent spatial distribution of magnetic fields generated by the electromagnetic flux compression technique is investigated, with emphasis on the dynamical processes of an imploding liner. The developing magnetic field distribution in space and time is determined by a three-dimensional implosion process of the liner that is settled in a primary coil, using an advanced numerical calculation.

Precise measurement of a magnetic field generated by the electromagnetic flux compression technique

The precision of the values of a magnetic field generated by electromagnetic flux compression was investigated in ultra-high magnetic fields of up to 700 T. In an attempt to calibrate the magnetic field measured by pickup coils, precise Faraday rotation (FR) measurements were conducted on optical (quartz and crown) glasses. A discernible "turn-around" phenomenon was observed in the FR signal as well as the pickup coils before the end of a liner implosion. We found that the magnetic field measured by pickup coils should be corrected by taking into account the high-frequency response of the signal transmission line. Near the peak magnetic field, however, the pickup coils failed to provide reliable values, leaving the FR measurement as the only method to precisely measure extremely high magnetic fields.

A copper-lined magnet coil with maximum field of 700 T for electromagnetic flux compression

A copper-lined (CL) primary coil, which is a composite of steel and copper, was devised for the electromagnetic flux compression technique to generate ultrahigh magnetic fields. The newly developed coil was found to be highly efficient for electromagnetic energy transfer and provided stabilization of the liner implosive motion with less influence from the current feeding gap. Dynamical current density distribution of the materials used in a primary coil was evaluated and applied to the design of the CL coil. Fields of up to 730 T were achieved by employing the CL coil with an energy injected from a 4 MJ condenser bank. This value is the highest achieved thus far in an indoor setting. The peak magnetic fields were found to depend significantly on the initial seed magnetic field. The optimum seed fields for obtaining the highest peak magnetic field were determined.

Increase of energy transfer efficiency in the electromagnetic flux compression technique generating ultra-high magnetic field

Magnetic fields of over 100 T can be generated only through the use of a destructive pulsed magnet. Electro-magnetic flux compression (EMFC) is an efficient method to generate such ultra-high magnetic fields. The EMFC system at Institute for Solid State Physics holds the world record for the highest magnetic field produced in-doors. This system has been used for various sorts of measurements applied to matters under ultrahigh magnetic fields. Recently, we successfully improved the coil system to generate a higher field using less energy injection and more simplified preparation processes. The new system increased the electro-magnetic energy transfer efficiency to at least twice that of the previously employed system. Our new primary coil using a copper current guide has the advantage of shallower high-frequency current skin depth and less contact impedance than previous ones. Therefore the discharge current spark is completely avoided. The improved skin depth resulted in a symmetric implosion of the liner coil with less influence of the feed gap. A high degree of cylindrical liner symmetry was observed during implosion. A fast liner speed of 2.4 km/s was achieved, and 350 T could be generated by 1 MJ and 470 T by 2 MJ.

Production of ultra-high magnetic fields and their application to solid state physics

A review is given on the recent progress of techniques for generating ultra-high magnetic fields in the megagauss range. Discussion is focused on the techniques using condenser bank discharge which have been developed at ISSP (Institute for Solid State Physics) with a view to applications in solid state physics. By the electromagnetic flux compression technique, pulsed high fields up to 350 T have been generated. By the single-turn coil technique, fields well above 150 T have been generated without destroying samples. The megagauss fields are succesfully applied in a variety of experiments.

Computer Simulation of Megagauss Field Generation by Electromagnetic Flux-Compression

The process of generating very high magnetic fields in the megagauss range by the electromagnetic flux-compression technique (Cnare's method) was simulated by computer. The fundametal equations of motion of the liner were numerically solved with a computer program, taking into account the accurate magnetic field distribution inside and outside the liner. The calculated results are in good agreement with our recent experiments. Calculation assuming the use of a very large capacitor bank shows a possible generation of more than 10 MG in a considerably large volume.