Gregory Benford, Professor Plasma Physics and Astrophysics (949) 824-5147
Professor Benford earned his Ph.D. from the University of California, San Diego in 1967. He is a member of Phi Beta Kappa, a Woodrow Wilson Fellow, and a consultant for NASA.
This program unites theoretical studies with a parallel experimental program in radiation processes of relativistic electron streams in plasma. Experiments use intense relativistic beams (10 kAmp, 700 keV) propagating in helium plasma. Microwave and atomic spectral (Stark shift) diagnostics measure emission and the underlying turbulent fields. The group also studies the practical methods of high-power microwave emission. Turbulence levels are high, with electric field energy densities comparable with the total thermal energy of the background plasma. Such strong fields demand new theory and sophisticated diagnostics, with fast time resolution (less than ten nanoseconds). This is a new regime -- "superstrong" turbulence -- with statistical properties just being explored.
These experiments and coupled theory apply to galactic jets, quasars, and pulsars. Emission by scattering of energetic electrons from plasma turbulence (which the beams themselves produce) can be much more powerful that the familiar single-particle processes such as synchrotron radiation. The extreme variability of quasars recently discovered in radio and optics may arise from such processes. Calculations of expected power and spectra imply that quasars could be powered by flows with less total energy than formerly expected. Much work needs to be done in relating these new, collective radiation mechanisms with both astrophysical and laboratory observations.
Teaching areas include general properties of strong turbulence and radiation, both in experiment and theory. Astrophysical applications of these fundamental areas are also of interest, such as the brilliant radio features (arcs, filaments, threads) recently found at our own galactic center, and their possible links with hypothesized black holes there.
Coherent Radiation from Energetic Electron Streams via Collisionless Bremmstrahlung in Electrical Plasma Turbulence, (with J. C. Weatherall), Astrophys. J. 378, 543 (1991).
Collective Emission from Rapidly Variable Quasars, Astrophys. J. 391, L59 (1992).
Electron Beam Radiation by Collective Compton Boosting of Strong Turbulence, (with J.C. Weatherall), Phys. Fluids B 4 (12) 4111 (1992).
Collective Radiation from Jets, Proceedings of the 7th IAP Astrophys. Meeting, Extragalactic Radio Sources from Beams to Jets, Paris, July 2-5 (1991).
Statistics of Strongly Turbulent Electric Fields, (with X.-L. Zhai), Phys. Fluids B 5 (6) 1914 (1993).