Relazione sulle attività svolte durante il Dottorato Giulia Cozzani
My PhD project focuses on the microphysics of magnetic reconnection in the near-Earth space, in particular on the structure of the Electron Diffusion Region (EDR), the micro-region in which both ions and electron are demagnetized. I investigate this topic by using both in situ data from the Magnetospheric MultiScale (MMS) mission and Eulerian kinetic Vlasov simulations. MMS is a NASA mission launched in 2015 and composed by four identically equipped spacecraft flying in a tetrahedral formation. Its unprecendent time resolution of particle data allows to study the magnetic reconnection process at electron scales.
The observational part of my PhD project started with an extended search of MMS sets of data (events) suited for studying the structure of the EDR at the magnetopause, both in terms of spacecraft orbit and inter-spacecraft separation. Then, I selected one EDR event with the smallest inter-spacecraft separation ( 6 km) which allowed me to perform a novel∼ 6 km) which allowed me to perform a novel
multi-spacecraft study highlighting the differences in field and particle signatures at electron scales.
I have extensively used magnetic field data from the flux-gate magnetometer, 3D electric field data from the axial and spin-plane probes and particles data from the fast plasma instrument. This allowed me to gathered expertise about MMS instrumentation, data and their
calibrations, which is required for this post-doctoral position. In particular, I have carefully analyzed MMS electric field data and I have treated in detail the associated experimental errors in collaboration with IRF-Uppsala. This error analysis was crucial to
quantitatively assess the energy conversion in the EDR, which is typically small and associated to large errors.
The results of this observational study indicated that the structure of the EDR at the
magnetopause can be much more complex than it has been found in other MMS events and than is usually depicted by PIC simulations. In particular, this study shows that EDR is rather inhomogeneous and that the pattern of the energy conversion is patchy, suggesting a possible turbulent structure and evolution of the EDR during reconnection. The results from this study have been published in Physical Review E journal (G. Cozzani, et al., 2019, In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection, Phys. Rev. E, 99, 043204.). An important signature found in this event, whose analysis is planned for a future study, is the existence of large amplitude and high-frequency waves in the EDR which are very localized since the waves signatures are not observed at all the four MMS
probes. These results suggest the the EDR may be the site of turbulence which might play a role for anomalous resistivity in the reconnection site.
The MMS data analysis carried out during the first part of my PhD have pointed out the need of simulations with high spatial resolution and low noise in order to understand the kinetic physics at play at electron scales. Following this motivation, the second part of my PhD has been tailored to study the EDR by using a fully-kinetic Eulerian algorithm solving the Vlasov-Maxwell system of equations in the so-called Darwin approximation (ViDA code). The ViDA code is specifically designed to improve our understanding of the kinetic dynamics of collisionless plasma at electron scales by giving access to the fine phase space details of the electron distribution function. This numerical tool is ideal to study many physical processes in the EDR and other electron-scale reconnection regions such as separatrices and jet fronts and, in particular, the processes responsible for the patchy structure of these regions, for turbulent anomalous resistivity, for intermittent heating and acceleration of electrons.
The ViDA code has been developed in the last year in the framework of a collaboration between Università di Pisa and Università della Calabria. I am one of the main contributors to this code for which I have been responsible for simulating magnetic reconnection in a
gathered in a paper that has been accepted for publication in the Journal of Plasma Physics (O. Pezzi, G. Cozzani et al., 2019, ViDA: a Vlasov-DArwin solver for plasma physics at
electron scales, Journal of Plasma Physics).
Besides developing and testing the code, I have performed 2D simulations of magnetic reconnection and I focused on the evaluation of
the different terms in the Ohm’s law which can be properly addressed by the ViDA code due to the very low computational noise of electromagnetic fields and particle distributions. I am also performing a very-high resolution simulation which is able to properly separate the electron scale from the Debye scale, aiming to understand whether the EDR has a turbulent or laminar structure at those scales and - if turbulence is present - to characterize the turbulence properties.
In general, the simulation part of my PhD project has given me valuable experience in designing and analyzing simulations addressing magnetic reconnection at the electron scale. I believe that the ViDA code can be a highly valuable tool since it can help the interpretation of MMS data of anomalous resistivity and other processes. In particular, this code allows for a cleaner computation of electron distribution functions compared to PIC codes, which is ideal to
support the interpretation of the complex measurements from the Fast Plasma Investigation MMS instrument.
Although my observational MMS studies have been mainly devoted to magnetic reconnection at the magnetopause, I have also analyzed magnetotail MMS data. In 2018, I have spent one month as invited visiting PhD student at Beihang University (Beijing, China) under the supervision of Prof. H. S. Fu, where I have learnt how to use methods of magnetic topology reconstruction such as the FOTE method which I have applied to a few cases (including the magnetopause event published in Physical Review E in 2019). I have selected a few
magnetotail EDR events which I will analyse in detail in the future in order to investigate the structure of the EDR, similarly to what I did for the magnetopause case. Also, I have participated to the Scientist-In-The-Loop (SITL) activity of the MMS mission which gave me the
possibility to examine data in other regions encountered by MMS (bowshock, solar wind and magnetosheath) beyond magnetopause and magnetotail.
Articoli pubblicati
• G. Cozzani, A. Retinò, F. Califano, A. Alexandrova, O. Le Contel, Y. Khotyaint-sev et al., (2019). In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection, Phys. Rev. E 99, 043204.
• O. Pezzi, G. Cozzani, F. Califano, F. Valentini, M. Guarrasi, E. Camporeale et al., (2019), ViDA: a Vlasov-DArwin solver for plasma physics at electron scales, accepted for publication in Journal of Plasma Physics.
• H. Breuillard, O. Le Contel, T. Chust, M. Berthomier, A. Retinò, D. L. Turner et al., (2018). The properties of lion roars and electron dynamics in mirror mode waves observed by the Magnetospheric MultiScale mission, Journal of Geophys-ical Research: Space Physics 123, 93–103.
• J. M. Webster, J. L. Burch, P. H. Reiff, A. G. Daou, K. J. Genestreti, D. B. Gra-ham et al., (2018). Magnetospheric Multiscale Dayside Reconnection Electron Diffusion Region Events, Journal of Geophysical Research: Space Physics 123, 4858–4878.
• Z. Wang, H. S. Fu, C. M. Liu, Y. Y. Liu, G. Cozzani, B. L. Giles et al., (2019). Electron distribution functions around a reconnection X-line resolved by the FOTE method, Geophysical Research Letters 46, 1195–1204.
• Z. Z. Chen, H. S. Fu, C. M. Liu, T. Y. Wang, R. E. Ergun, G. Cozzani et al., (2019). Electron-driven dissipation in a tailward flow burst, Geophysical Re-search Letters 46, 5698–5706.
Workshop and conferenze
• EGU 2019, Vienna, Austria, Apr 8-12, 2019. (poster)
• ISSI Team: Magnetic Topology Effects on Energy Dissipation in Turbulent Plasma (second meeting), ISSI Beijing, Beijing, China, Sept 3-7, 2018.
• 3rd MMS Community Workshop, Bergen, Norway, June 11-14, 2018. (oral) • AGU Fall Meeting 2017, New Orleans, LA, USA, Dec 11-15, 2017. (oral)
• ISSI Team: Magnetic Topology Effects on Energy Dissipation in Turbulent Plasma (first meeting), ISSI Bern, Bern, Switzerland, Nov 13-18, 2017.
• SF2A 2017, Paris, France, Jul 4-7, 2017. (poster)
• 2nd MMS Science Community Meeting, Boulder, CO, USA, June 6-8, 2017. (oral) • Toulouse Reconnection Workshop, Toulouse, France, May 9-12, 2017. (oral) • EGU 2017, Vienna, Austria, Apr 24-28, 2017. (poster)
• AGU Fall Meeting 2016, San Francisco, CA, USA, Dec 12-16, 2016. (poster) • MMS Science Working Team Meeting, Uppsala, Sweden, Jun 13-17, 2016. Summer school e formazioni
• “26 th summer school on parallel computing”, CINECA, Bologna, Italy, 15-26 May 2017. • Simulations numériques et calculs hautes-performance, 9-14 January 2017, Maison de la Simulation, CEA.
• Description fluide et cinétique des plasmas, 16-21 January 2017, Observatoire de Meudon. • Accueil sécurité doctorants 2016/2017, 29 November 2017, École Polytechnique, Palaiseau. • E-IntePro : Intégrité professionnelle, 21 September 2017, Campus des Cordeliers, Paris. Altre attività
• Fête de la Science, stand of the LABEX Plas@Par, UPMC, Paris, France, Oct 14-16. Three days were dedicated to the explanation of basic concepts of plasma physics and simple experiments, to the students of the primary school and general public.
