Research
My work revolves around theory, simulations, and radio observations of astrophysical magnetic fields. I describe two specific areas of my research below.
My work revolves around theory, simulations, and radio observations of astrophysical magnetic fields. I describe two specific areas of my research below.
Small-scale turbulent Dynamo
Small-scale turbulent Dynamo
The exponential amplification (kinematic stage) of weak seed magnetic fields in a turbulent medium eventually slows down and saturates (saturated stage) due to the back reaction by the Lorentz force. This process is referred to as the small-scale dynamo. The properties of seed fields (as long as it is weak) do not affect the properties of the dynamo generated magnetic fields. The magnetic fields achieve a (statistically) more force-free state as it saturates. The spatially intermittent random (magnetic energy concentrated in random filaments and sheets) magnetic field structures are also larger in the saturated stage (right panel) as compared to the kinematic stage (left panel). The small-scale dynamo saturation is physically explained by a decrease in the amplification and an increase in the diffusion of magnetic fields.
References:
Turbulent dynamo in the two-phase interstellar medium
Saturation mechanism of the fluctuation dynamo in supersonic turbulent plasmas
Seed magnetic fields in turbulent small-scale dynamos
Saturation mechanism of the fluctuation dynamo at Pr_M >= 1
Saturation of Zeldovich stretch–twist–fold map dynamos
The exponential amplification (kinematic stage) of weak seed magnetic fields in a turbulent medium eventually slows down and saturates (saturated stage) due to the back reaction by the Lorentz force. This process is referred to as the small-scale dynamo. The properties of seed fields (as long as it is weak) do not affect the properties of the dynamo generated magnetic fields. The magnetic fields achieve a (statistically) more force-free state as it saturates. The spatially intermittent random (magnetic energy concentrated in random filaments and sheets) magnetic field structures are also larger in the saturated stage (right panel) as compared to the kinematic stage (left panel). The small-scale dynamo saturation is physically explained by a decrease in the amplification and an increase in the diffusion of magnetic fields.
References:
Turbulent dynamo in the two-phase interstellar medium
Saturation mechanism of the fluctuation dynamo in supersonic turbulent plasmas
Seed magnetic fields in turbulent small-scale dynamos
Saturation mechanism of the fluctuation dynamo at Pr_M >= 1
Saturation of Zeldovich stretch–twist–fold map dynamos
Cosmic ray propagation and energy equipartition between cosmic rays and magnetic fields in galaxies
Cosmic ray propagation and energy equipartition between cosmic rays and magnetic fields in galaxies
Cosmic rays are relativistic charged particles. In spiral galaxies, the cosmic ray energy density is comparable to the turbulent, thermal, and magnetic energy densities. Low-energy cosmic rays primarily diffuse in the interstellar medium of galaxies and the presence of intermittent magnetic fields at smaller scales alters the cosmic ray diffusion. Left panel: trajectory of a cosmic ray particle propagating in an intermittent random magnetic field obtained by solving equations of nonlinear small-scale dynamo, the color shows the magnetic field strength normalized to its maximum value along the trajectory. The particle performs gyrations in strong field regions (following magnetic field lines) but is also scattered in relatively weak field regions. Right panel: trajectories for an ensemble of particles with Larmor radius less than the magnetic field correlation length and same initial spatial location within the numerical domain but random velocity directions (different coloured lines are for particles with different initial velocity directions). The particle distribution over large scales in time and length becomes isotropic due to numerous scattering events, which leads to cosmic ray diffusion.
Cosmic rays are relativistic charged particles. In spiral galaxies, the cosmic ray energy density is comparable to the turbulent, thermal, and magnetic energy densities. Low-energy cosmic rays primarily diffuse in the interstellar medium of galaxies and the presence of intermittent magnetic fields at smaller scales alters the cosmic ray diffusion. Left panel: trajectory of a cosmic ray particle propagating in an intermittent random magnetic field obtained by solving equations of nonlinear small-scale dynamo, the color shows the magnetic field strength normalized to its maximum value along the trajectory. The particle performs gyrations in strong field regions (following magnetic field lines) but is also scattered in relatively weak field regions. Right panel: trajectories for an ensemble of particles with Larmor radius less than the magnetic field correlation length and same initial spatial location within the numerical domain but random velocity directions (different coloured lines are for particles with different initial velocity directions). The particle distribution over large scales in time and length becomes isotropic due to numerous scattering events, which leads to cosmic ray diffusion.
In star-forming galaxies, energy equipartition between cosmic rays and magnetic field energy densities is often assumed to extract magnetic field information from synchrotron observations. Such an assumption does not hold at smaller scales and one must be aware of the dynamical scales in the system before using the energy-equipartition argument.
In star-forming galaxies, energy equipartition between cosmic rays and magnetic field energy densities is often assumed to extract magnetic field information from synchrotron observations. Such an assumption does not hold at smaller scales and one must be aware of the dynamical scales in the system before using the energy-equipartition argument.