Particle experiments and simulations

I am a professor of space physics at the Department of Physics and Astronomy, University of Turku, Finland, and the head of Space Research Laboratory (SRL), which performs experimental, theoretical and computational research on high-energy phenomena in near-Earth space. SRL continuously collaborates with several research groups in Finland and abroad and most of our research projects are joint efforts with a large number of researchers working on the same topics. SRL develops instrumentation for detecting energetic charged particles and numerical simulation codes to understand the propagation of charged particles through electromagnetic fields in space.


Topics of my research

Solar energetic particles (SEPs). The Sun produces very energetic particles during solar eruptions, i.e., solar flares and coronal mass ejections (CMEs). These outburst of energetic particles are called SEP events or solar particle events. Because they can penetrate thick layers of material, SEPs constitute a severe radiation risk to humans and electronics in space. Together with my research group and collaborators, I study the acceleration of SEPs close to the Sun and their transport in the interplanetary medium to near-Earth space and beyond, as well as the near-Earth radiation environment generated by SEPs.

Shock waves are transitions from supersonic to subsonic flow associated with compression (i.e., increase of density) and dissipation (i.e., conversion of ordered kinetic energy of the flow to random thermal energy). In ordinary gases, shocks have thicknesses of the order of the collisional mean free path of the molecular motion. In dilute space plasmas, binary collisions are too infrequent to account for the dissipation and re-distribution of energy. Instead, collective processes involving fluctuating electromagnetic fields take the role of collisions. Such shocks are termed collisionless shocks. In the absence of binary collisions, collisionless shocks generate energetic particle populations (such as SEPs) and together with my research group and collaborators, I focus on understanding this acceleration process in detail.

Turbulence is ubiquitous in all fast flows. Plasma turbulence differs from ordinary fluid turbulence since in addition to flow velocity, density and temperature, also the electromagnetic fields fluctuate and exert forces on the plasma. Also the dissipation mechanisms are more versatile in plasmas than in ordinary gases. Together with my research group and collaborators, I study the generation and evolution of electromagnetic fluctuations in (space) plasmas, focusing on the interaction of the fluctuations with the (energetic) charged particles of the plasma.

My research topics require the use of kinetic theory, which means that one needs to consider the motion of particles in 6-dimensional phase space, where in addition to regular three spatial dimensions, the three components of velocity form another three dimensions. In addition to developing our own kinetic simulation codes to study particle acceleration at the Sun, we also make use of the world’s most advanced kinetic simulation framework, The Vlasiator, developed by Prof. Minna Palmroth’s research group at the Finnish Meteorological Institute.


Courses I teach

  • Fysiikan matemaattiset apuneuvot II (4 ECTS, in Finnish)
    Probability — Fourier series — Integral transforms — Partial differential equations
  • Introduction to plasma physics (4 ECTS)
    Basic plasma concepts — single particle theory — kinetic theory — macroscopic theory — MHD — cold plasma waves — warm plasma
  • Hydrodynamics and hydromagnetics (8 ECTS)
    Introduction — Boltzmann equation — Derivation of hydrodynamic equations — Ideal fluids — Viscous fluids — Gas dynamics — Waves and instabilities — Turbulence — Rotation in hydrodynamics — Magnetohydrodynamics
  • Plasma astrophysics (8 ECTS)
    Plasma physics and electrodynamics revisited — Observations of astrophysical plasmas — Supersonic flows and shocks — Energetic particle transport in plasmas — Particle acceleration in plasmas


Publications

My publications can be found on NASA/ADS and on ResearcherID.


Curriculum Vitae

I graduated from the University of Turku (MSc in theoretical physics) in 1993 and started to pursue the PhD degree in space physics. I defended my dissertation on Monte Carlo simulations of interplanetary transport and acceleration of energetic particles in 1998. I carried on as a postdoc in Turku until 2002, when I joined the space physics group in the University of Helsinki for a two-year postdoc. Following this, in 2004, I was nominated as a university lecturer in theoretical physics (space physics) in the University of Helsinki, where I stayed until the end of 2013. As of January 1, 2014, I have held my present position as a professor of space physics in my alma mater.

My more-or-less-complete CV can be found here.