Theory and numerical simulations suggest that lasers can create doughnut plasma wakes for positron acceleration in compact plasma accelerators. One of the fundamental challenges for designing a plasma based linear collider is to accelerate positrons in non-linear plasma wakefields. Researchers have long considered that this regime, which can lead to very high accelerating fields, could not be used to accelerate positrons. Using particle-in-cell numerical simulations, EPP team member Jorge Vieira in collaboration with José Tito Mendonça from the Group for Lasers and Plasmas at IST, showed that lasers carrying angular orbital momentum excite doughnut shaped strongly non-linear plasma waves for high-energy positron acceleration. These results may then open the way for future designs of compact plasma based linear colliders in strongly non-linear regimes. More information can be found here.

The largest plasma based acceleration experiment in the world has been approved at CERN. This experiment will use 0.5 TeV proton bunches to drive intense plasma waves capable to accelerate particles to high energies. One of the physical questions to be clarified is the role of the background ion motion. This work carried out by EPP team members Jorge Vieira, Ricardo Fonseca and Luís Silva, in collaboration with Warren Mori from University of California, Los Angeles, shows that the the background plasma ion motion can strongly reduce accelerating fields. The work also identifies gases that could be used to avoid the deleterious effects associated with the motion of the background plasma ions. More information can be found here.

One of the challenges in future plasma based acceleration experiments at CERN and at SLAC using long hadron and lepton bunches is to stabilise the driver beam propagation for long propagation distances. In these experiments the beam dynamics will be dominated by competing mechanisms between self-modulation, which leads to large accelerating fields, and hosing, which leads to beam break-up. The work by EPP team member Jorge Vieira in collaboration with Patric Muggli from Max Planck Institute for Physics in Munich and Warren Mori from University of California, Los Angeles, shows conditions where a new mechanism for hosing suppression can operate. More information can be found here.

The universe is filled with magnetic fields. However, it is widely accepted that in the early universe they did not exist. An important scientific question is how these magnetic fields could have grown from nothing to the level we find them today. epp team members, Ricardo Fonseca and Luís O. Silva, collaborated with  Kevin Schoeffler, and Nuno Loureiro on a paper published in Physical Review Letters addressing this issue. They demonstrate using first principle simulations how magnetic fields are formed by only gradients in the pressure and density. This generation of magnetic fields also plays an important role in many high power laser experiments, which generate magnetic fields on the order of megagauss. These fields form via both the previously predicted Biermann battery mechanism as well as a kinetic plasma instability known as the Weibel instability, depending on the system parameters. These results should have an important impact on both the…

Prof. Sakai (Kyoto University), the pioneer of plasma metamaterials, has visited GoLP to deliver a GoLP VIP Seminar on March 26 and to discuss ongoing collaborations and joint projects on plasma metamaterials

The IUPAP General Relativity and Gravitation Young Scientist Prize 2014 was awarded to Jorge Santos, epp team alumni (2002-2005). This is one of the most prestigious prizes for young scientists working in General Relativity. Jorge concluded his MSc at IST in 2005 on parametric instabilities driven by white light, from which resulted two papers (Physical Review Letters and Journal of Mathematical Physics). Jorge is now a Lecturer in Cambridge University, on leave at Stanford University.

 
Paper ’Seeding of Self-Modulation Instability of a Long Electron Bunch in a Plasma’ by Y. Fang et al was published in Physical Review Letters. It describes a series of experiments performed in the Accelerator Test Facility (ATF) at Brookhaven National Laboratory demonstrating the seeding of the self-modulation instability by long bunches with sharp rise density profiles. This work supports the concept of similar experiments in the future, e.g. Self-Modulation Instability (SMI) experiments using long bunches of relativistic protons. More information can be read here.

Prof. Mattias Marklund, from Chalmers University, visited GoLP from February 9 to February 14. A world expert in strong field physics and an ERC Grant awardee, Prof, Marklund interacted with the team members, with the goal of pushing forward ongoing collaborative projects and to explore new projects for collaboration.

IST magazine Valores Próprios, Number 2 features an interview with Frederico Fiúza, epp team alumni, describing his experience while working and doing research at GoLP.

Paper “Exploring the nature of collisionless shocks under laboratory conditions” by Anne Stockem et al. was published in Scientific Reports. It addresses the transition between electrostatic and electromagnetic shocks and identifies the relevant regimes for an efficient acceleration of ions and a realisation in the laboratory. More information can be read here.