Obituary of Luis Gomberoff

The distinguished scientist and professor of the “Departamento de Física” of the “Facultad de Ciencias” of the “Universidad de Chile”, was born on November 17 1941, and obtained his M.Sc in Physics in our institution in 1964. In 1967 he obtained a Ph.D. in Mathematical Physics at the London University, England. He was a professor at Tel Aviv University until 1980, and he also worked in France and Princeton.

He is the author of more than 140 ISI publications, and other publications, adding to about 200 total publications.

Prof. Gomberoff had wide ranging interests in physics. His first contributions were in particle and quantum field theory. He went to the physics department at Tel-Aviv University in 1970 after completing his Ph.D degree in England, where he had fruitful collaboration with Yuval Neeman and others. Although many of his results on chiral symmetry breaking, on deformation of current algebra, scaling and sum rules, have been subsumed in later, more complete, theories one still senses the intelligence and intellectual curiosity of his mind.

He started working in plasmas when there was great hope for controlled nuclear fusion. Influenced by high energy physics he developed a quantum field approach to plasma physics. It is precisely in plasma physics that he had some of his most relevant contributions, not only in controlled nuclear fusion, but also in space physics, with important publications on the solar wind, the Earth’s magnetosphere, the neutron star, among others.

For more than three decades, Prof. Gomberoff has made novel contributions to the theory of linear and nonlinear waves and instabilities in magnetospheric and solar wind plasmas and in electron positron plasmas. A consistent theme of his work has been the inclusion of multiple ions species having different temperatures and drifting with respect to each other. This is the situation observed in the solar wind, with the additional complication that the particle distribution functions are usually not Maxwellians. Prof. Gomberoff’s work has illuminated many interesting effects whereby the ions affect wave and instability dispersion relations, thereby altering how the particles interact, especially resonantly, with the electromagnetic field. This work offered possible explanations of how the ions acquire drifts, high temperatures, and non-Maxwellian distributions in the first place. He was particularly cognizant of the fact that the solar wind contains large-amplitude MHD waves, and in recent years he devoted much effort to understanding the parametric instabilities of these waves in multi-ion plasmas, and the sometimes surprising effects of the nonlinear waves on other instabilities (such as a stabilizing effect on the same linear instabilities that triggered them, or the onset of explosive instabilities). It is becoming evident that parametric instabilities play a role in the production and evolution of the turbulence itself, as well as the generation of nonthermal distribution functions in the solar wind plasma.

During the 70’s and 80’s Prof. Gomberoff published several seminal papers on the convective growth of electromagnetic ion cyclotron waves in the multi-ion magnetospheric plasma. Specifically, he showed how the combination of cold and hot ions in the medium influences both the excitation and the propagation characteristics of these important magnetospheric waves. This work, which is still referred to today, has had a major impact on our understanding of the processes that affect dynamical changes in the Earth’s radiation belts.

Luis developed an analytical method in the context of the broadband electrostatic noise in the Magnetotail, which provided a simple way to understand many aspects of the role of ion-ion instabilities and the ion-acoustic instability depending on various parameters. This was applied, for example, to the electrostatic bursts in the Comet Giacobini-Zinner.

In his early studies Luis and his coworkers studied the effects of a cold plasma component on the ion-cyclotron instability under magnetospheric conditions. He showed that heavier particles influence the relevant growth rates. Motivated by the observed half-harmonic shifted electric emission from various areas in the magnetosphere he studied multi-streams instabilities. The effects of temperature of the various plasma components and the non-resonant interaction between them were studied, explaining the unexpected shape of the electron distribution function in the ISEE1 measurements.

In parallel, Luis studied convection in cylindrical current carrying plasmas, caused mostly by resistivity and thermal conductivity. He showed a complete analogy to fluid convection with an onset determined by a Reyleigh number.

Prof. Gomberoff was one of the pioneers of plasma physics education in Chile and Latinoamerica, with important contributions to scientific conferences and workshops, and produced many successful Ph.D and master students.