Come along to R22 Pickavance Lecture Theatre or join online to hear from Professor Gianluca Gregori (University of Oxford) on the topic of laboratory astrophysics experiments.

Date: Thursday 24th September 2026

Time: 14:00 – 15:30

There will be coffee/tea served in R22 Coffee Lounge at 15:30. All welcome.

Campus members with RAL site passes wishing to attend in person, please go straight to Pickavance Lecture Theatre.

Campus members without RAL site passes and non-campus members wishing to attend, please use the Zoom link to attend the talk remotely.

New perspectives in laboratory astrophysics experiments: new accelerator experiments probe the stability of ultra relativistic pair beams

High power lasers and particle accelerators investigate astrophysical phenomena. 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, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to numerical and analytical studies.

We 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. We 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-long plasma, analogous to TeV γ-ray induced pair cascades in the intergalactic medium. We show that our experiment provides fundamental insights on how beams of energetic particles interact with the background plasma, possibly explaining the observed lack of reprocessed GeV emission from TeV blazars. We conclude by discussing how acceleration of cosmic rays can occur in our laboratory analogues of pair jets.

About the speaker:

Prof Gregori is a Fellow of the American Physical Society and a Fellow of the Institute of Physics.

Prof Gregori research interests cover laboratory astrophysics with high power lasers, dense plasmas as found in the interior of stars and planets, and inertial confinement fusion (ICF) energy. He started at Oxford University in October 2007 as an RCUK Fellow in the Department of Atomic and Laser Physics. In 2012 he became a Fellow and Tutor of Physics at Lady Margaret Hall, and in 2013 he was appointed Professor of Physics.

You can read more here.