Questions tagged [plasma-physics]

Theory, lab and space experiments, and calculations related the physics of plasmas, i.e., matter constituted by ionized atoms.

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37 views

Electron distribution in Low Earth Orbit

I have been searching online for some kind of pdf function that describes the charged electron distribution in Low Earth Orbit in regards to their energies. Any ideas on whether something like that ...
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Application of Darboux's theorem to magnetic field line flows

In this famous paper by Cary and Littlejohn on noncanonical Hamiltonian mechanics and its application to magnetic field line flow, they claim that as a result of Darboux's theorem, it is always ...
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What is a quasi-axisymmetric stellarator?

I know that a tokamak is a donut shape fusion confinement device with an axisymmetric magnetic field configuration. The stellarator is similar but its field configuration is non-axisymmetric. I've ...
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143 views

RF-sputtering: where comes the target self-bias voltage from?

While learning for an exam, I stumbled over the following Question: According to Material Science of thin Films by Milton Ohring, "RF sputtering essentially works because the target self-biases ...
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Quantifying electrical energy stored in a plasma

The energy stored in the electric field in a medium is given by $U = \frac{1}{2} \epsilon E^2$, where $\epsilon$ is the permittivity in the medium and $E$ is the electric field. When considering a ...
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Colors of the Aurora

I've seen several web pages that attempt to explain the colours of the aurora but they seem to gloss over or leave out certain details, so I'm still confused. For example, this page explains it in ...
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Difference between speed of sound into a star

I try to understand the following graphics with x-axis being the radius of a typical star : I would like to knwo if $\delta c/c$ represents the relative error between theorical and experimental ...
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What is the Relative Radiation Absorbtion per unit Mass of the various states of matter?

I am trying to find information on the relative merits of using a gas, liquid, solid or even a plasma as a radiation shield. Examples Ice, water and water vapour. Iron, molten Iron, Iron ...
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42 views

How do poloidal and toroidal field lines become single helical lines?

In a tokamak, there are toroidal and poloidal fields created by separate sources. The resultant picture typically visualized are helical field lines in the tokamak. I am simply wondering: is this a ...
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Does the stretch twist fold dynamo reconnect at any point?

At the end of the folding of the magnetic field lines, it appears as though two loops are stacked above one another to increase the total magnetic flux. But are these two loops themselves connected at ...
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In what cases should plasmas be considered compressible?

I was listening to a lecture where it was mentioned incompressibility was assumed during derivation of an electrostatic instability, but incompressibility was not assumed for an electromagnetic ...
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Using superconducting coils as a transformer

In experiments such as tokamaks, typically an ohmic transformer (primary) is used to produce current in the plasma (secondary) by swinging from to the most positive to negative magnetic field. Ideally ...
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Is magnetic reconnection possible in vacuum?

Magnetic reconnection occurs due to flux-breaking behaviour (e.g. finite resistivity) in a medium. But can reconnection be observed in a vacuum (where there may be virtual particles)? Has this been ...
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Can inductance be dependent on direction in plasmas?

Inductance is given by the ratio of magnetic flux to the current. For a given plasma at a particular density and temperature (which itself could be a tensor), one may define $$L = {\Phi(i) \over i},$$ ...
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How to handle electron-electron or proton-proton repulsion in Cosmology?

In Scott Dodleson's book, he considers that baryons are all tightly coupled. I know this can be proved by calculating the interaction time scales and comparing with Hubble's Expansion time scale. ...
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Plane waves in plasmas

Waves in plasmas can be classified as electromagnetic or electrostatic according to whether or not there is an oscillating magnetic field. A corresponding wiki article states: Applying Faraday's ...
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Are both ions and electrons assumed to be moving in plasma currents?

In a tokamak plasma, for example, an ohmic transformer is used to inductively drive current. In this scenario, is it simply assumed that the electrons are mobile and driving all the current in a ...
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What determines direction of plasma current in tokamaks?

Plasma current is used to ohmically heat fusion plasmas and provide stabilization of grad-B drift in tokamaks as the resulting poloidal motion of the charged particles results in the particles ...
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Speed of sound in non-conformal strongly coupled plasma?

For a conformal system in (d+1)-dimensions, the speed of sound is given by $ v_{s} = 1/\sqrt{d}$ (for ex : $\mathcal{N}=4$ SYM in four dimensions). Is it possible to have a non-conformal strongly ...
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Are microwave-generating devices (gyrotrons) in the ITER system phased to heat plasma?

Provided electricity from grid is converted and supplies 24 gyrotrons, which generate electromagnetic waves, which in turn, will transfer their energy to the electrons of the ITER plasma to heat it up....
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What is the difference between granulation and supergranulation in the Sun's photosphere?

Granulation and super granulation seem to be some sort confused topics as they are due to the heated particles coming out of the surface. What is the difference between the two?
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Speed of sound at the Sun surface [closed]

The gas velocity at the Sun's surface is subsonic and At 1 AU from the sun, the solar wind is supersonic. Like Parker wind solution. Why the velocity at the Sun's surface is subsonic? (In the ...
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27 views

Multipoint to plane corona discharge

I'm trying to make a multipoint to plane corona discharge, my cathode is a piece of metal with needles welded on it, and my anode is also a piece of metal. The experiment i was setting up is to treat ...
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56 views

Can wind blow away the ionised gases created by plasma/arc lighters

I understand that for plasma lighters to work, they ionise the air between the electrodes. I am wondering what happens to these ionised gases during lighting. Do they remain ionised for a while and ...
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What affects the lifespan of plasma

When I was reading up ion thruster and ionocraft, I saw this concept of plasma lifespan. But I can't find any information or study done on what affect the lifespan of plasma. Is it pressure? Electric ...
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What is an active region in sun's photosphere? Why sometimes there is an active region but no sunspots?

What is the theory behind an active region? If we check data in solar monitors, there are some cases where there is no sunspot but there is still an active region. Why is that the case?
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How to compute Coulomb scattering rate(in early universe)?

I want to compare Coulomb scattering rate with Hubble's expansion rate. To compute Coulomb scattering rate, I know that $$ \Gamma = n_p\sigma v_{rel} $$ Here, $\sigma = \frac{e^{4}}{(4\pi\...
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Artificial Plasma Creation

It is intuitive that at high temperature matter converts into plasma because of intense energy of electrons that they break away from atoms. But how can plasma be created at low pressures?
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Plasma in solids

One way to create plasma is to focus a very powerful laser pulse to a small beam waist. In gaseous atoms, ionization will occur, yielding a soup of ions and electrons, which we call a plasma. But ...
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59 views

Pulsed source in Finite Difference Time Domain simulations

I want to simulate a resonator cavity with a medium inside with FDTD method. The medium has a resonant frequency $\omega_R$. I want to find ratio of outgoing $P_{out}$ power to the incoming power $P_{...
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Derivation of average momentum change in diffusive shock acceleration

I am trying to figure out a specific step in the derivation of the power law spectrum for cosmic ray particles upon diffusive shock acceleration. I am working with Drury 1983 (pdf link) but I have ...
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565 views

Why should potassium serve to stabilize a welding arc?

Of the many types of electric arc welding electrodes, there are two that consist of a steel core surrounded by a coating of “High cellulose sodium” and “High cellulose potassium.” The web sites (for ...
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Magnetic confinement in a tokamak

I have a question about why exactly the twisting of the field lines in a Tokamak solves the magnetic confinement issue. My understanding is that the magnetic confinement issue arises in the toroidal ...
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How do bulk regions of clouds conduct charges into a lightning bolt?

It's easy to find explanations of the theories of charge accumulation in clouds during storms, as well as ones describing suspected processes leading to lightning channel formation. What I have yet to ...
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Plasmons : doubts about the derivation of the Heisenberg equation of electrons' density

I'm studying plasmons from "Haken-Quantum Field Theory of Solids", and i need some help in the calculation of the equation of motion of eletrons' density \begin{equation} \hat{\rho}_{\overrightarrow{q}...
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Why does plasmon have higher erngy than phonon?

In my mind plasmon is movement of electrons and phonon is movement of atoms in an lattice. movement of atoms should have a large energy because atom is larger.
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Difference between MHD turbulance and Alfvenic turbulence?

I'm quiet confused in reading literatures involved MHD turbulance and Alfvenic turbulence, it seems they are pointing to the same notion in most of the content. Please explain the difference of them?
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Reaction Rate Coefficient

Janev et al. in their book Elementary Processes in Hydrogen-Helium Plasmas say that the reaction rate $\langle\sigma v\rangle$ of a certain collision with cross-section $\sigma(v_r)$ for a particle of ...
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Bulk viscosity in jump conditions for shock waves

One of the jump conditions for shock waves can be derived from the Navier-Stokes equation and it takes the form (see Shu, Gas dynamics, p.212) $\dfrac{d}{dx}\left(\rho u^2 + P - \frac{4}{3}\mu \frac{...
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Why is there a color difference in DC glow discharge?

Image:DC discharge tube[Reddish region is anode glow, Bluish Region is cathode glow] I have recently started Plasma physics. I want to understand why there is a color difference in the anode glow and ...
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How do I visualize the in-homogeneous magnetic field?

In a Magnetic field, there are 4 terms (divergence, gradient, curvature and twist). I understand the divergence and gradient terms but why is the curvature term represented with $\frac{\partial B_x}{\...
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286 views

Questions about plasma

Imagine if you were to heat liquid mercury until it reaches a plasma state. Would it be possible to completely separate the free electrons (ions) from the positively charged nuclei (cations)? Next, ...
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Filling a flux surface in a tokamak or stellarator

Assume you have a magnetic confinement device like a tokamak or a stellarator. Let's assume further a configuration with closed magnetic field lines resulting in typical flux surfaces. If you now ...
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What is the upper limit on the speed of sound in a relativistic plasma?

What is the theoretical limit to sound speed in a plasma? In a monoatomic gas, it can be demonstrated that the equation of state in the relativistic regime is given by $\rho = \rho_0 + 3p/c^2$, ...
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134 views

Is a dipole fusion reactor feasible?

It is well known that the earth's dipole-like magnetic field is able to confine charged particles to paths that spiral along the field lines. That's why we have auroras and the Van Allen radiation ...
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Can plasma cast a shadow [duplicate]

I was on Science fiction and fantasy and there was a question on wether or not a lightsaber can cast a shadow, but that would depend on wether or not plasma can cast a shadow. I became curios and I ...
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Sufficient conditions for Rayleigh-Taylor instability

I was reading the paper entitled "The Rayleigh—Taylor instability in astrophysical fluids" by Allen & Hughes (1984), and they discuss relativistically hot plasmas in the context of weak magnetic ...
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The interstellar medium reflects extremely low-frequency radio waves. Could we use this fact to build a more efficient photon rocket?

According to the equations of MHD, electromagnetic waves cannot propagate in a plasma if they are below the plasma frequency. (For more information, see this question about astronomical-wavelength ...
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Characteristics of plasma accelerators

I've been reading about plasma accelerators but I do not understand the main differences between a plasma accelerator and a "normal" one. In the case of LHC for example, if we have free protons ...
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Pulsed transmission of electromagnetic waves through a plasma

A plasma has the following dispersion relation: $$k^2 = \frac{\omega^2}{c^2}\left(1 - \frac{\omega_\mathrm{p}^2}{\omega^2}\right) $$ where $k$ is the magnitude of the wave-vector and $\omega$ is the ...