Megagauss physics

Fields greater than 10 MG can be produced by explosive flux compression and fields up to 3 MG with capacitor banks. Measurement of fields up to 10 MG is reliable, but difficulties may be expected at higher fields. Megagauss fields have been applied successfully as high-pressure sources, in high-energy particle physics, and in solid-state investigations. Other uses remain to be exploited: plasma compression by megagauss fields has been relatively unsuccessful but shows promise; their use as particle accelerators has been studied only theoretically; and much work remains to be done, both experimentally and theoretically, in connection with applications of megagauss fields in solidstate physics. Note added in proof: Since this article was prepared, Grigor'ev et al. have carried out some experiments (48) in which they have compressed hydrogen up to a density of 1.95 grams per cubic centimeter with a calculated pressure of 8 x 10(6) atmospheres. They report five different pressure-density points and claim that their data can be explained by assuming that the transition to the metallic phase occurs at a pressure of 2.8 x 10(6) atmospheres, with a density change from 1.08 to 1.3 g/cm(3). Using the flux compression techniques described earlier in this article, Hawke et al. [see (30, 31)] have obtained a pressure-density point at 1.5 x 10(6) atmospheres and 1.0 g/cm(3), which is also not inconsistent with a predicted equation of state of metallic hydrogen (49). In view of the experimental uncertainties, none of the pressure-density data can yet be used conclusively to establish the transition's existence. Hawke and his co-workers are presently engaged in measurements of the electrical conductivity of the compressed hydrogen. Observation of a significant conductivity at the proposed transition pressure would be a more definitive test of a metallic transition. In addition, two lower pressure-density points have been obtained for deuterium by the Los Alamos group, by means of the flux compression methods described earlier in this article. One point agrees to within experimental error with a slight extrapolation of Stewart's data (50). The second point is at a pressure of 65+/- 3 x 10(3) atmospheres with a density of 0.71 +/- 0.10 g/cm(3). The data are tentative, and efforts are under way to obtain more data points at both higher and lower pressures.