A post submitted by CGI member ScienceTruth.

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The Winnemucca Institute for Advanced Studies presents

The Electric Double Layer

Structures in Laboratory and Space Plasmas

The Electric Double Layer phenomena has an important history for many decades in laboratories here on Earth. In outer space it has a more recent history. Let's investigate the earthly laboratory history first.

In the Electric Double Layer, oppositely charged particles attract each other and tend to collect at the surface of each substance, but remain separated from one another by the finite size of each particle, or by neutral molecules that surround the charged particles. The electrostatic attraction between the two opposite and separated charges causes an electric field to be established across the interface between them.

The electric field generated within an Electric Double Layer (DL) has a major influence on physical and chemical processes that occur at these Phase Boundaries. For example, in electro-chemical cells where the fundamental process involves the transfer of electrons between a metallic electrode and a solution (like in a battery), small changes in the electric field strength across the interface produce large changes in the flow rate of the electrons. In industrial processes, consideration of the electric field strength across the interface is also important in which it is desired to transfer a substance across an electrode-solution boundary, such as the deposition of metal from a solution (electro-plating in a liquid bath), or the dissolution of a metal electrode. The concept of an Electric Double Layer is essential to the understanding of a large group of electric phenomena associated with the movement of a solid in a liquid medium - e.g., colloidal particles dispersed in solution, or the movement of a liquid along a fixed solid - e.g., the flow of liquid through a capillary tube.

The charging of a capacitor with a solution shows the positively charged ions attaching to the negatively charged electrode. This layer of positive ions then lightly attracts negatively charged ions in the solution. The positive electrode follows this same trend, only it attracts negatively charged ions.

Double-Layer capacitance is the storing of electric energy by means of the electric double layer effect. The amount of electric charge stored in double-layer capacitance is linearly proportional to the applied voltage. The unit of capacitance is the Farad.

Double Layer capacitance is when an electrode and a liquid solution are touching each other, causing the charges to line up and allowing electricity to be stored there (battery again). The double layer is created when the electrode’s surface is charged through the application of electricity. This causes oppositely charged molecules to be attracted to the surface. This first layer is well attached to the electrode surface, causing it to be semi-permanent. The second layer (with opposite charge) is held by this first layer, making it less attached to the electrode than the first layer. These two layers are separated by a single atomic layer of uncharged molecules in the solution. These alternating layers of charges have the ability to store electric energy, in a way that depends on the amount of electricity initially applied to the electrode. Once this charge is stored in the device, the source of electricity can be removed and the circuit can still be powered from the stored electricity contained in the device.

In Space Plasmas, Electric Double Layers (DL) will also form

" Two characteristic signatures are associated with DLs, particle acceleration and energy dissipation. These features
make the DL very interesting in many different plasma environments spanning from laboratory experiments to astrophysics.

" Electric double layers are like cliffs of potential (like a riverbed waterfall) and can energize charged particles falling through them. They exist in the plasma environment of the Earth, and of the Stars; and can cause phenomena as diverse as aurorae in luminous draperies in the polar sky, and electromagnetic radiation from central stellar objects in Planetary Nebulae called pulsars, like in the Crab Nebula.

" We have discovered a Double Layer in our laboratory plasma systems, and measured the energy of the highly supersonic ions it has accelerated. The fascinating part is that the Double Layer is not triggered by forcing two plasmas to interact, but it self-generates under certain parameters, much like a riverbed suddenly falling away to create a waterfall. We are optimizing this effect to create a very efficient thruster for interplanetary spacecraft.

" The Helicon Double Layer Thruster (HDLT) is being developed in the Space Plasma, Power, and Propulsion Group led by Professor Christine Charles at the Research School of Physics at The Australian National University in Canberra, Australia.

" Dr Christine Charles has invented the world's first Helicon Double Layer Thruster or HDLT. This new propulsion concept has the potential to propel humans to Mars and beyond and greatly decrease the costs of maintaining satellites and spacecraft in their desired orbits. " [1]

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" Electric double layers (DLs) are transient or stationary localized potential structures which form in space plasmas, laboratory plasmas, and numerical simulations of plasmas. Since the early analytical work of Langmuir, there have been a number of analytical propositions such as the ion acoustic shock wave, the B.G.K. solution of the Vlasov equation (the simplest collision model for the kinetic equation), and other works, followed by reviews on laboratory current-driven and current-free DLs. From the early 1980s DLs have been experimentally measured in the Earth's auroral plasma using probes on polar-orbiting satellites. They cause the acceleration of charged particles in the magnetospheres of Earth and Jupiter that generate auroral displays. Their existence has been proposed in solar flares and in the solar corona. They can be created in a broad range of laboratory plasmas such as constricted gas discharges, Q-machines and triple plasma devices, laser-produced plasmas, tandem mirrors, and expanding unmagnetized or magnetized plasmas. Emerging fields of research in medicine and pharmacology are currently reporting on the importance of DLs and the understanding of charged particle transport in colloid and interface science. The direct connection between double layers and particle acceleration / heating, has generated interest in their laboratory control for the development of various thrusters such as the Helicon Double Layer Thruster, the Helicon plasma thruster, and the electrothermal “Pocket Rocket” thruster: these studies also relate to the physics of geometric and magnetic nozzles.

DLs are ubiquitous but differ vastly in properties: they can be propagating or stationary, weak or strong ΔΦDL / (kBTe ~ 1 to 2, 000 where kBTe is the electron temperature in units of eV electron volts, in single or multiple steps, relativistic or non-relativistic, narrow or wide i.e. Δz/λD ~ 10 to 1, 000 where λD is the Debye length, in current-driven or current-free.
Current-free DLs were first analytically proposed by Perkins and Sun and experimentally demonstrated by zero-current operation of Q-machines, two-electron-temperature plasma expansion in vacuum, and lately in low pressure expanding magnetized radiofrequency plasmas in diverging or converging-diverging magnetic nozzles. Schrittwieser has discussed the complex analytical challenge in understanding whether a DL can form in an absolutely collisionless plasma i.e. in vacuum, a low-collisional plasma, or a collisional plasma. Andrews and Allen have analytically described their formation as a boundary layer between two plasmas, generated at about 1 Torr, in a constricted gas discharge tube containing a cathode and an anode. Holleinstein et al. have shown the role of turbulent collisions in a potential jump, generated in a low-pressure argon plasma at 0.4 mTorr. [2]

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*** Hannes Alfvén described an Electric Double Layer as, "...a plasma formation by which a plasma, in the physical meaning of this word, protects itself from the environment. It is analogous to a cell wall by which a plasma, in the biological meaning of this word, protects itself from the environment."

Double Layers might very well cutoff the current flow in a galactic circuit causing a catastrophic rise in voltage. This powerful energy release, or "exploding double layer", is what mainstream astronomers call a "supernova" or a "gamma ray burst".

Alfvén, said in 1986: "Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested that x-ray and gamma ray bursts may be due to exploding double layers. In solar flares, DLs with voltages of 10^9 Volts or even more may occur, and in galactic phenomena, we may have voltages that are several orders of magnitude larger."

Alfvén's proposed idea of "exploding double layers" is one of the foundational principles for cosmic ray generation, because they can generate cosmic rays at extreme energies. Cosmic rays are ionized particles. The majority of cosmic rays are single protons, but nuclei as heavy as uranium have been detected. As consensus mainstream theories state, heavy particles are accelerated to relativistic velocities by unknown forces and then whipped out into the galaxy like a shotgun blast, scattering in every direction.

" Localized, quasi-static parallel electric fields that are created as a result of charge separation in plasmas have been studied by scientists over the last century and have become known as double layers (DLs). DLs are important because they can efficiently accelerate charged particles, dissipate energy, and cause a local break in the existence of large scale existing magnetic fields. As a result, they are expected to be an important process in many different types of space plasmas, as well as here on Earth and on many other astrophysical objects. Over the last century it is now a well-established fact that DL's do occur naturally in space plasmas. " [3]

[1] The Helicon Double Layer Thruster (HDLT) is being developed in the Space Plasma, Power and Propulsion Group (led by Professor Christine Charles) at the Research School of Physics at The Australian National University in Canberra, Australia.

[2] Current-Free Electric Double Layer in a Small Collisional Plasma Thruster Nozzle Simulation
Teck Seng HoTeck Seng HoChristine Charles Christine Charles*Roderick W. BoswellRoderick W. Boswell

Space Plasma, Power and Propulsion Laboratory, Research School of Physics, The Australian National University, Canberra, ACT, Australia

[3] The Search for Double Layers in Space Plasmas
L. Andersson and R. E. Ergun
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA

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Wikipedia and a number of other websites and Papers also contributed small bits, all of which were subject to 'editing', some to remove the many reference markers [##] for a smoother flow for the reader, especially as in [2].

Information provided herein by the Winnemucca Institute for Advanced Studies is for educational purposes. Our ‘Man on the Street Series’ of informative Science Papers is designed to provide a semi-technical answer to everyday experiences.