Speaker

Prof. Gianluca Gregori – University of Oxford

Seminar abstract

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be sites of particle acceleration.

So far, the experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited.

Prof. Gregori will present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron accelerator. He will show that the characteristic scales necessary for collective plasma behaviour, such as the Debye length and the collision less skin depth, are exceeded by the measured size of the produced pair beams.

In the first application of this experimental platform, the stability of the pair beam is studied as it propagates through a meter-length plasma, analogous to TeV γ-ray induced pair cascades in the intergalactic medium.

We conclude by discussing how these experiments can provide fundamental insights on beams of energetic particles interacting with the background plasma and possibly explaining the observed lack of reprocessed GeV emission from TeV blazars.

Bio

In 2001, Prof. Gregori received his PhD in Mechanical Engineering from the University of Minnesota, Minneapolis.

From 2001 to 2005 he worked at the Lawrence Livermore National Laboratory in the National Ignition Facility directorate. From 2005-2007 he was staff scientist at the Rutherford Appleton Laboratory, and in 2007 he started his appointment in the Department of Physics at the University of Oxford. Since 2013 Prof. Gregori is fellow of Lady Margaret Hall.

Prof. Gregori’s research interests include laboratory astrophysics (in particular, Fireball experiment at CERN), inertial confinement fusion, dense plasma simulations, and beyond the Standard Model (axion searches and acceleration radiation).

ATS Seminar Organisers
A. Dallocchio (EN), E. Metral (BE), M. Modena (ATS-DO), T. Stora (SY), A. Sublet (TE)