In this episode, we will explore what the Plasma Universe is and some of the basic principles
that govern it. I want to explore how Antony Peratt extended much of Hannes Alfven early
work to explore some alternative concepts for the formation of galaxies and clusters
of galaxies. We will start with a basic overview of what the Plasma Universe is and examine
the filamentary electric-current aspect of cosmic plasmas.
An Introduction to the PLASMA UNIVERSE
It is a model of the universe in which the plasma and electromagnetic forces play a significant
role. The origin of this concept comes from the plasma work conducted in the 1950’s
onwards which revealed many surprises in terms of how plasmas behave and showed many similarities
to cosmological phenomena. One important aspect of plasma cosmology is the idea of starting
from the observed present-state and trying to extrapolate backwards in time to an even
more ancient time.
So from this, the first important point is that plasma cosmology rejects the idea of
the Big Bang. The universe is not expanding and did not form from the Big Bang. Now at
this stage, there are no clear concepts about how it formed but going back to the point
about working backwards this would be an end goal but in order to try and understand this,
you would have to work outwards from what we can observe. And this is exactly what they
focused on.
Plasma cosmology holds that the basic laws of plasma physics that we can observe in the
laboratory and in the magnetosphere, as well as the heliospheric plasma also apply to interstellar
and intergalactic plasma
Space is filled with a network of currents which transfer energy and momentum over vast
distances. These currents often pinch to filamentary or surface currents. The latter of these will
give rise to a cellular structure in both interstellar and intergalactic space.
In order to understand the phenomena in certain regions, it is necessary to map not only the
magnetic but most importantly the electric field and the electric currents.
A number of plasma phenomena, like double layers, Birkeland currents, critical velocity,
the pinch effect and the properties of electric circuits are vitally important to understanding
cosmological phenomena.
Our concept of cosmic plasma has changed considerably. Essential differences between the old and
new paradigms include the following: Electric double layers are now known to accelerate
charged particles to kilovolt energies in the terrestrial magnetosphere
The necessity of a global electric current description to describe the transfer of energy
in magnetised cosmic plasmas. This leads to the requirement of drawing the circuits in
which the current flows. This approach also emphasises the discrete particle description
in simulating cosmic phenomena, where particle currents may be explicitly followed.
In the magnetospheres, plasmas exist in both active and passive states; this is probably
true for all cosmic plasma. Cosmic plasmas are often not homogeneous,
instead exhibit filamentary structures which are likely to be associated with currents
parallel to the magnetic field. In the magnetospheres there are thin stable
current layers which separate regions of different magnetisation, density, and temperature.
In the case where a current flows in a partially ionised plasma, a chemical separation may
take place. Due to this and other effects, space plasmas have a general tendency to be
separated into regions of different chemical compositions.
The similarity of the measured radio spectra from cosmic sources and that of the dense
plasma focus and other pulsed power laboratory devices leads to the idea that plasma physics
can be used to account for these phenomena.
Galactic dimensioned Birkeland filaments
An electromotive force which gives rise to electrical currents in a conducting media
is produced whenever this current flows perpendicular to magnetic field lines. Falthammar give a
very nice explanation of why they are of great importance:
A reason why Birkeland currents are particularly interesting is that, in the plasma forced
to carry them, they cause a number of plasma physical processes to occur. These include
waves, instabilities and fine structure formations. These in turn lead to consequences such as
acceleration of charged particles, both positive and negative, and element separation. Both
of these classes of phenomena should have a general astrophysical insterest far beyond
that of understanding the space environment of our own Earth.
Birkeland currents in the Laboratoty plasma
In the laboratory, filementary structures are a common morphology exhibited by energetic
plasmas. In dense plasma focus machines we often see a filamentary magnetic rope like
structure. High-resolution etchings of electron beams onto witness plates show nearly identical
vortex profiles ranging from a dimension of a few micrometres in the dense plasma focus,
and a few centrimeters in cathode electron beams. This size variation of nearly 4 orders
of magnitude is extended to nearly nine orders when auroral vortex recordings are directly
compared to the laboratory data.
When we examine the magnitude of the current in these filaments, fine detail resolution
of currents filaments shows indistinguishable vortex patterns over nearly 12 orders of magnitude
while coarser resolution shows that the phenomena probably transcends at least 14 order of magnitude,
from microampere to multimega ampere electron beams.
Birkeland currents in cosmic plasma
As far as we know, most cosmic low-density plasmas also depict filamentary structures.
As an example we find filamentary structures in the following cosmic plasmas, all of which
are associated with or likely associated with electric currents:
In the aurora, filaments are often observed forming parallel to the magnetic field. These
have dimensions down to about 100m Inverted V events and the in-situ measurements
of strong electric fields in the magnetosphere demonstrate the existence of filamentary structures.
These would carry a current of between 10^5 and 10^6 Amps and span a distance of 10^8m
In the ionosphere of Venus, flux ropes are observed who are typically about 20km or 2x10^4m
In the sun, prominences, spicules, coronal streamers, polar plumes all show filamentary
structure. Prominences are thought to carry a current of around 10^11 Amps.
Cometary tails often have a pronounced filamentary structure
In the interstellar medium and in interstellar clouds there is an abundance of filamentary
structures In the centre of the galaxy there are twisting
plasma filaments, apparently held together by a magnetic field possessing both azimuthal
and poloidal components. These extend for nearly 500 light-years so 5 x 10^18m
Within the radio bright lobes of double radio galaxies, where filament lengths may exceed
20kpc or 6x10^20m
The formation of Double Layers Within Birkeland currents. In magnetised nonhomogenous astrophysical
plasma, a number of mechanisms are present that can generate field-aligned electric fields.
These include anomalous resistivity caused by wave-particle interactions, collisionless
thermoelectric effects due to energy-dependent wave-particle interactions, magnetic mirror
effects involving trapped particles and magnetic field gradients, and electric double layers
leading to localised charge separation.
All of these have been studied in the laboratory and simulated by computer, it is the last
mechanism that has been found to be remarkably prolific in producing appreciable potential
drops in neutral plasma.
These double-layers seem to be strongly associated with Birkeland currents. Both experimental
and computer simulations have shown the formation of a series of double layers along with current-carrying
plasma columns or filaments.
When double layers form in adjacent Birkeland current filaments, field-aligned electric
fields are generated, which then serve to accelerate electrons within these regions.
Peratt in his paper on the Evolution of the Plasma Universe wanted to extend the study
of cosmic plasma to the case of the galactic dimensioned, so 50kpc in width, Birkeland
filaments by means of three-dimensional, fully electromagnetic, and relativistic particle
in cell simulations. The simulation model consists of modelling a magnetic field aligned
neutral plasma filament in the presence of a field-aligned electric field. To study the
evolution of the interacting filaments, a second filament was placed adjacent to the
first. He investigated as many as 6 filament interactions. Due to the 1/r force between
filaments, it appeared that a majority of cosmic plasma phenomena are the result of
two, or at most three interactions among the closest filaments.
Synchrotron radiation from Bennet Pinched Filaments
One of the most important processes that limit energies attainable in particle accelerators
is the radiative loss by electrons accelerated by the magnetic field of a betatron or synchrotron.
This mechanism was first brought to the attention of astronomers by Afven and Herlofson. Which
at the time was a remarkable suggestion as plasma, magnetic field and laboratory physics
were thought to have little if anything to do with a cosmos filled with island universes,
galaxies.
Synchrotron radiation is characterised by a generation of frequencies appreciably higher
than the cyclotron frequency electrons, continuous spectra whose intensity decreases with frequency
beyond a critical frequency, increasing beam directivity and strongly polarized electromagnetic
wave vectors.
The discovery of this mechanism has made it possible to infer that high energy particles
exist in many types of astronomical objects and has provided evidence of extensive magnetic
fields and most importantly it has shown that enormous amounts of energy may indeed be generated,
stored and released in cosmic plasma.
Charged particle beams held together or pinched by their self magnetic fields have been of
general interest since their earliest investigations by Bennet. The macroscopic picture of such
a beam is that of a self-consistent magnetic confinement or compression against the expansion
due to thermal pressure. On the microscopic scale, the individual particle orbits include
radial oscillations due to the Lorentz force superimposed on the drift in the direction
of mean flow. These are the betatron oscillations. Since they imply particle acceleration, there
is electromagnetic radiation associated with them. Because the force is a v x B force,
the radiation from the relativistic electrons is synchrotron radiation.
In the laboratory experiments, the morphology of the radiating plasma at radiation burst
is both helical and filamentary. This shape only occurs when there are two wires which
interact electromagnetically. This means initially the two-column will be attracted to each other.
In computer simulations of two filaments interacting it was found that whenever the attractive
force between columns causes their separation to be reduced to a distance such that the
repulsive force starts to become comparable to the attractive force, a burst in the radiation
occurs. In the simulation, this distance equated to about the order of several pinch radii
This interaction between two Birkeland currents is something we will explore in the next video.